Icing Physics Studies Using the 3D SIDRM Test Article: 2023 Icing Tests Analysis

Appendix A provides nominal locations of surface mounted thermocouples (Table A.1), internally located

Appendix A provides nominal locations of surface mounted thermocouples (Table A.1), internally located thermocouples near the leading edge (Table A.2), heat flux gauges located in pockets on the inner mold line (Table A.3), and the heat flux gauges’ built-in thermocouples (Table A.4). This report primarily focuses on the surface temperatures, but locations of all the other thermocouples and heat flux gauges are provided in the appendix for completeness and for reference purposes.

Figure 5 is a schematic that indicates the general location of many surface thermocouples and pressure taps on the instrumented side and leading edge. There are 64 pressure taps built into the SIDRM test article.

There are 32 taps wrapping around chordwise on each of the test article extensions, each row located about 17.25 in. from the span center. There is some staggering of taps at the leading edge. The appendix provides nominal locations of pressure taps located on the test article outer mold line (Table A.5).

For reference, the profile geometry of the SIDRM main body is provided in Table A.6 of the Appendix.

Additional details of the struts locations and dimensions are also provided.

Instrumented Strut P206 P217 P216 P215 P210 P211 P212 P209 P208 P207 P213 P214

· ·

· · · · · · · · · · ·

Staggered LE taps as viewed down z - axis P218 ST2 T407 ST1 x ST2

· ·

ST1 T401

Flow T301

71.8 in

· · · · · · · · · · · · ·

T303 T302 T311 T312 T313 T314 T315 T304 T305 T310 z T306

· ·

T207 T201 Leading Edge ( T 3 07 under strut) P118

· · · · · · · · · · · · ·

P113 P116 P115 P112 P114 P117 P107 P108 P109 P110 P111 P106

62.6 in

Figure 5.—Schematic of pressure tap and thermocouple locations on SIDRM. The opposite side (non-instrumented side) is not shown but the pressure tap locations mirror the side that is shown (instrumented side), aside from those shown near the leading edge.

NASA/CR-2026000820 7

3.0 Addressing IRT Reference Pressure Issue Impacts

An issue with pressure measurements was noticed some time after testing had been completed. A reference pressure tube in the IRT pressure system was disconnected and identified as the source of the issue. It was determined that the reference pressure tube had been disconnected starting September 16, 2022, until the issue had been discovered on April 1, 2024. The reading from this pressure line dictates control of the airspeed within the wind tunnel. With incorrect pressure values, the airspeed control system provided erroneous airspeed ( U ) and liquid water content ( LWC ) at the test section. This SIDRM test entry took place in early 2023 and was impacted by this issue. The data was reprocessed with corrected airspeeds and LWC values. Table 1 shows the target airspeed and the approximate corrected airspeed rounded to 0.5 knots for reference. Table 1 shows that the corrected airspeed is greater than the target, with negligible discrepancies at lower airspeeds, but larger differences with increasing airspeed. The deviation between target LWC and corrected LWC is a more complex calculation involving various condition settings, with corrected values ranging from 1 to 3% lower than the intended LWC for supercooled liquid water icing tests. Ice crystal icing tests utilize the same spray nozzle injection system, with liquid water glaciating as the cloud traveled from the spray bar to the test section. There is a component of ice crystals recirculating in the closed loop tunnel that contributes to the overall ice water content ( IWC ) at the test section.

Reprocessing for corrected IWC is not possible, and it is unknown how the reference pressure tube and airspeed discrepancy impacted IWC for the ice crystal icing tests. For this report, the IWC is treated as if there was no impact from the reference pressure issue.

Part of the test objectives was to conduct some repeat test runs from 2022, however this reference pressure tube reference issue adds some variance. The first SIDRM test entry took place in early 2022 and was not impacted by this reference pressure tube issue, with all data previously reported remaining accurate.

Comparisons between 2022 and 2023 tests will be limited accordingly in this report.

For reference, all ice accretion tests were conducted with target airspeeds of 150 and 200 knots. Most aerodynamic tests were conducted at target airspeeds of 100, 150, and 200 knots, with a select few test points conducted at 50 knots. Figures and tables in the following sections will be displayed with the corrected airspeed.

TABLE 1.—TARGET AIRSPEEDS COMPARED TO APPROXIMATE CORRECTED AIRSPEEDS, AS A REFERENCE Target, Approximate U , corrected, knots U , knots 50 50.0 100 100.5 150 152.5 200 207.0 NASA/CR-2026000820 8

4.0 Aerodynamic Tests

4.1 Aerodynamic Test Objectives and Test Conditions

Multiple objectives where set for the aerodynamic tests to help characterize surface flow around the SIDRM test article and are listed below.

• Assess the impact of an air gap between the test article and the test section ceiling (approximately 0.5 in. gap).

• Conduct a series of AOA sweeps at various airspeeds to understand the parameter impact on surface pressure and flow characteristics.

• Compare aerodynamic measurements against SIDRM tests conducted in 2022 to assess repeatability.

• Conduct tests that pinpoint the stagnation line at the leading edge.

Aerodynamic tests conducted in 2022 were performed utilizing 1° AOA intervals. Because the model was symmetric, the stagnation line was expected to be at the leading edge highlight location at 0° AOA .

However, the aerodynamic data from 2022 suggested that the stagnation line formed at the leading edge highlight was not at 0° AOA , but at an angle between 0° and 1°. Aerodynamic tests conducted in 2023 were performed with smaller AOA intervals around 0° AOA to zero-in on the AOA that put the stagnation line at the leading-edge highlight of the model. Table 2 shows the AOA sweeps conducted at different airspeeds, U . The total air temperature was held constant for all aerodynamic test runs at T = 5 °C.

The pressure coefficient, C , (nondimensional) was calculated from experimental measurements.

p Equation (1) shows the pressure coefficient expression where P is the surface pressure as measured by the tap built-in pressure taps, P is the freestream static pressure, and P is the total pressure. Total and static pressure s 0 measurements were made by pitot-static probes located at the beginning of the constant area test section.

𝑃𝑃 −𝑃𝑃 𝑡𝑡𝑡𝑡𝑡𝑡 𝑠𝑠 𝐶𝐶 = (1) 𝑝𝑝 𝑃𝑃 −𝑃𝑃 0 𝑠𝑠

4.2 Ceiling Gap Flow Impact Investigation

The SIDRM test article was purposely designed and constructed to not span the full height of the IRT test section. This is standard practice to ensure that the test article fits when installed. A foam cut-out that matches the contour of the test article was placed in the gap to ensure full uniform flow around the test article. For the initial entry in 2022 the foam cut-out extended the entire chord length, however the aft portion of the cut-out was difficult to contain in the gap during testing. Tests were ultimately conducted with just the forward portion of the foam cut-out installed in the gap that extended from the leading edge portion of the cut-out was difficult to contain in the gap during testing. Tests were ultimately conducted with just the forward portion of the foam cut-out installed in the gap that extended from the leading edge to approximately 25% of the chord. This same forward portion foam cut-out was used in the 2023 test entry.

Figure 6 shows the foam cut-out inserted in the gap and its chordwise extent.

TABLE 2.—TEST CONDITIONS FOR THEAERODYNAMIC CHARACTERIZATION RUNS T U , AOA , 0, °C knots ° 5 50.0 0.0, 4.0 5 100.5 –0.8, –0.6, –0.4, –0.2, 0.0, 0.1, 0.2, 0.4, 1.0, 2.0, 3.0, 4.0 5 152.5 –0.4, –0.2, 0.0, 0.2, 0.3, 0.4, 1.0, 2.0, 3.0, 4.0 5 207.0 –0.4, –0.2, 0.0, 0.2, 0.3, 0.4, 0.6, 1.0, 2.0, 3.0, 4.0 NASA/CR-2026000820 9 Figure 7 shows pressure coefficient values plotted against normalized chord length, where each graph compares pressure tap measurements between the lower and upper rows. AOA values of 0° (Panels (A) to (C)) and 4° (Panels (D) to (F)) are shown at U = 100.5, 152.5 and 207 knots. The figure shows that there is good matching between the lower and upper tap row pressure measurements for the forward 30% of the chord for all angles of attack and airspeeds. This coincides with where the foam cutout exists to fill the gap between the test article and the ceiling, likely aiding in uniform measurement between the rows for the forward 30%. Noticeable deviations occur between the tap row measurements starting at z/c = –0.4, and likely an influence of the ~0.5-in. gap at the ceiling. The C peak at z/c = –0.4 is lower for the upper row of p taps, suggesting some air flows towards the gap, resulting in slower flow for the upper portions around the maximum thickness of the SIDRM test article as compared to the lower portion.

Also of note, in Figure 7 is that there are asymmetric pressure measurements that occurred in the aft portion of the test article for the lower tap row between the instrumented and non-instrumented sides at AOA = 0°. This lower tap row asymmetry becomes greater as airspeed increased (Panels (B) and (C)).

Symmetric measurements are expected at AOA = 0°. More study is needed to verify, but a few hypotheses are posited. Physical inspection of the test article showed that the geometry was within tolerance of geometry design. However, the inspection occurred in an ambient environment (no flow), and it is possible that the fiberglass extension panels in which these pressure taps were located may have flexed under aerodynamic loads, and geometric asymmetries may have resulted. In addition, the bottom fiberglass extension panels were removed for test article installation in the IRT test section. A second hypothesis is that there is asymmetric airflow that develops in the closed-loop tunnel, in particular with the relatively thick test article (21.68 in. at maximum thickness) installed in the 108-in. wide test section. The upper tap row pressure measurements maintain symmetry along the entire chord for all airspeeds at AOA = 0°, suggesting that the ceiling gap helps equalize any pressure differences between the two sides due to any flow or geometry asymmetries that may exist.

A B Leading edge Extent of foam gap cut - out and its approximate corresponding Extent of foam extent down the gap cut - out span Leading edge Figure 6.—Images showing the extent of the foam cutout to fill the ~0.5-in. gap between the SIDRM test article and the ceiling as viewed (A) from above the plexiglass ceiling and (B) from inside the test section.

NASA/CR-2026000820 10 U = 100.5 Knots, Upper - Lower Tap Row Comparison U = 100.5 Knots, Upper - Lower Tap Row Comparison -3.5 -3.5 4° AOA Lower 0° AOA Lower -3 -3 D A 0° AOA Upper 4° AOA Upper -2.5 -2.5 -2 -2 pressure side -1.5 -1.5 -1 -1 suction -0.5 -0.5 side suction Pressure Coefficient Pressure Coefficient 0 0 side pressure 0.5 0.5 side 1 1 1.5 1.5 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 z/c z/c U = 152.5 Knots, Upper - Lower Tap Row Comparison U = 152.5 Knots, Upper - Lower Tap Row Comparison -3.5 -3.5 0° AOA Lower 4° AOA Lower -3 -3 E B 0° AOA Upper 4° AOA Upper -2.5 -2.5 -2 -2 Instrumented side -1.5 -1.5 -1 -1 Non - instr. side -0.5 -0.5 Pressure Coefficient Pressure Coefficient 0 0 0.5 0.5 1 1 1.5 1.5 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 z/c z/c U = 207 Knots, Upper - Lower Tap Row Comparison U = 207 Knots, Upper - Lower Tap Row Comparison -3.5 -3.5 4° AOA Lower 0° AOA Lower -3 -3 F C 4° AOA Upper 0° AOA Upper -2.5 -2.5 -2 -2 Instrumented side -1.5 -1.5 -1 -1 Non - instr. side -0.5 -0.5 Pressure Coefficient Pressure Coefficient 0 0 0.5 0.5 1 1 1.5 1.5 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 z/c z/c Figure 7.—Comparison of pressure coefficient values versus normalized chord length for the upper and lower tap rows. Values are provided at AOA = 0° (A) to (C) and 4° (D) to (F) for airspeeds of U = 100.5, 152.5, and 207 knots.

Despite some aerodynamic irregularities, the forward portion of the test article shows good surface pressure symmetry at AOA = 0°, and good agreement between the upper and lower tap rows for all aerodynamic tests conducted. The forward surfaces encounter favorable pressure, whereas the aft surfaces encounter adverse pressure which is unfavorable and susceptible to impacts of separation. The foam cutout aided good forward aerodynamic measurements, which is the focus of all icing tests, and it is believed that icing was not impacted by any aerodynamic irregularities that occurred on the aft portions due to the ceiling gap.

NASA/CR-2026000820 11

4.3 Angle of Attack and Airspeed Sweeps

Figure 8 shows pressure coefficient values plotted against normalized chord length for various angles of attack at airspeeds of U = 100.5, 152.5, and 207 knots. Both lower (Panels (A) to (C)) and upper (Panels (D) to (F)) tap row measurements are provided. The 1° AOA increments show how measured surface pressures were impacted. The C increasingly became more negative on the suction side near the leading p edge as AOA increased, indicating a local increase in air speed around the leading edge surface. A stagnation value of C = 1 occurred near the leading edge and will be explored more in Section 4.5. The location of p maximum test article thickness occurs at z/c = –0.42. The spike in C that occurs at z/c = –0.4 for each graph p corresponds to the tap nearest this maximum thickness and indicates the chord location where airspeed is greatest.

Of note in Figure 8 is that at a positive AOA the lift generated at the front half of the test article is countered by negative lift on the aft half. In the forward half, the upper curves represent the suction side, the lower curves represent the pressure side (see pressure and suction descriptions written in Figure 8(A)).

Integrating the difference between the two provides the amount of positive lift (an upward force) generated by the forward half. In the aft half, the upper curves represent the pressure side, the lower curves the suction side. The integrated difference now produces negative lift (a downward force) on the aft half. These countering forces act to effectively rotate the test article around its center axis. These countering forces become greater as AOA increases. It should be noted that the SIDRM geometry was not designed to be an efficient lifting surface but intended to investigate icing on the forward portion of the test article, where nonzero AOA tests, in part, provide data on collection efficiency shadow and concentration regions.

Flow separation occurred towards the trailing edge, where AOA impacted the location of flow separation.

Figure 8(C) provides the clearest example where flow separation was measured at z/c = –0.8 for the suction side but was still attached on the pressure side at this chord location. Flow separation occurred farther aft on the pressure side at z/c = –0.9. For positive AOA , flow separation was likely delayed until farther down the chord due to the favorable pressure gradient keeping the flow attached on the pressure side.

As was mentioned in Section 4.2, differences are again noticeable between the upper and lower pressure tap row measurements for the aft portion of the test article in Figure 8. This reinforces how the ceiling gap that exists towards the aft portion of the test article likely accounts for the differences. For the lower tap row, there is a deviation in C between the suction and pressure sides as AOA increases, but that difference p is washed out for the upper row of taps. Some air flow towards the ceiling gap likely accounts for this C washing out effect. In addition, flow separation is delayed in the upper tap row on the suction side p ( z/c = –0.9) compared to the lower tap row ( z/c = –0.8). To reduce the number of graphs displayed, only the lower pressure tap row will be provided for the remaining figures in this section. The lower pressure tap row represents a truer pressure flow profile where flow is constrained by the floor and is 2-dimensional (2D), unlike the upper tap row where some air flows laterally towards the ceiling gap and flow is unintentionally 3-dimensional (3D) towards the aft portion of the test article.

Figure 9 shows pressure coefficient measurements of the lower pressure tap row for two airspeed sweeps to more easily identify its impact on aerodynamics. Panels (A) and (B) show airspeed sweeps at AOA = 0 and 4°, respectively. In both graphs, the continuously decreasing value of C (more negative) at p 6 6 z/c = –0.4 with increasing airspeed is due to Reynolds number effect (Re = 1×10 to 5×10 ) (Ref. 53).

Greater momentum from faster airspeeds pushes the location of separation farther downstream, which in turn aids airspeed and affects C upstream at the model’s thickest width.

p NASA/CR-2026000820 12 U = 100.5 Knots, Upper Row U = 100.5 Knots, Lower Row -3.5 -3.5 0° AOA 0° AOA D A -3 -3 1° AOA 1° AOA -2.5 -2.5 2° AOA 2° AOA suction 3° AOA 3° AOA pressure -2 -2 side 4° AOA 4° AOA side -1.5 -1.5 -1 -1 suction side -0.5 -0.5 suction side 0 Pressure Coefficient 0 Pressure Coefficient 0.5 0.5 pressure 1 1 side 1.5 1.5 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 z/c z/c U = 152.5 Knots, Upper Row U = 152.5 Knots, Lower Row -3.5 -3.5 0° AOA 0° AOA -3 -3 E B 1° AOA 1° AOA -2.5 -2.5 2° AOA 2° AOA -2 -2 3° AOA 3° AOA 4° AOA 4° AOA -1.5 -1.5 -1 -1 -0.5 -0.5 0 Pressure Coefficient 0 Pressure Coefficient 0.5 0.5 1 1 1.5 1.5 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 z/c z/c U = 207 Knots, Lower Row U = 207 Knots, Upper Row -3.5 -3.5 0° AOA 0° AOA -3 C -3 F 1° AOA 1° AOA -2.5 -2.5 2° AOA 2° AOA -2 -2 3° AOA 3° AOA 4° AOA 4° AOA -1.5 -1.5 -1 -1 -0.5 -0.5 Pressure Coefficient 0 0 Pressure Coefficient 0.5 0.5 1 1 1.5 1.5 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 z/c z/c Figure 8.—Pressure coefficient values versus normalized chord length for angles of attack that range from AOA = 0 to 4° for airspeeds of U = 100.5, 152.5, and 207 knots. Both lower (A) to (C) and upper (D) to (F) tap row values are provided.

NASA/CR-2026000820 13 AoA = 0 ° , Lower Row AoA = 4 ° , Lower Row -3.5 -3.5 50.0 Knots 50.0 Knots -3 -3 B A 100.5 Knots 100.5 Knots -2.5 152.5 Knots -2.5 152.5 Knots Non - instr.

207.0 Knots 207.0 Knots -2 -2 suction side pressure Instrumented side -1.5 -1.5 side side -1 -1 suction Non - instr.

suction -0.5 -0.5 side side side Non - instr.

0 0 Pressure Coefficient Pressure Coefficient side pressure 0.5 0.5 side Instrumented 1 1 side 1.5 1.5 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 z/c z/c Figure 9.—Pressure coefficient values versus normalized chord length for velocity sweeps at angles of attack at AOA = 0 and 4°.

In the AOA = 4° graph, the C increasingly became more negative on the suction side near the leading p edge as U increased. This shows that there is a local increase in air speed around the leading edge surface, as negative C values indicate air flow speeds greater than far-field airspeed.

p Figure 9(A) shows that there are asymmetric pressure measurements that occurred in the aft portion of the test article between the instrumented and non-instrumented sides, despite AOA = 0°. This asymmetry becomes greater as airspeed increases. This reiterates and highlights the asymmetric measurements at AOA = 0° discussed in Section 4.2.

4.4 Comparison of 2023 to 2022 Measurements

Aerodynamic measurements acquired during the 2023 SIDRM tests are compared against those from the 2022 tests in Figure 10. During the 2023 tests, conditions were set with the intention of determining repeatability between the two test entries. As noted in Section 3.0, reference pressure issues that were only identified after testing was completed resulted in greater than intended airspeeds. These airspeed differences are noted in each graph in the figure. Despite airspeed differences, comparisons are made to evaluate repeatability and understand how small airspeed differences might impact pressure measurement.

Figure 10 shows pressure coefficient values plotted against normalized chord length for AOA = 0 and 4° where the target airspeeds were U = 100, 150, and 200 knots. The corrected airspeeds for tests conducted in 2023 are shown in the graphs. For perfect repeatability, the solid red curve would be plotted precisely on top of the dashed red curve, for example. The best repeatability occurs at the slowest target speed, and greater deviations occur at the two faster target airspeeds. At the lowest target airspeed, the differences in actual airspeed are negligible ( U = 100 vs. 100.5 knots) and provides the best repeatability comparison. The actual airspeeds differ more significantly for the fastest target airspeed ( U = 200 vs. 207 knots) and may be the reason for the poorer repeatability comparison. Despite any actual airspeed differences, the forward portion of the test article showed better repeatability (curves more closely plotted on top of each other) than the aft portion. This is favorable as ice accretion tests largely focus on the forward portion of the test article.

NASA/CR-2026000820 14 Lower Row Lower Row -3.5 -3.5 0° AOA, 152.5 kn - 2023 0° AOA, 100.5 kn - 2023 -3 -3 A B 0° AOA, 150 kn - 2022 0° AOA, 100 kn - 2022 -2.5 -2.5 4° AOA, 152.5 kn - 2023 4° AOA, 100.5 kn - 2023 4° AOA, 150 kn - 2022 4° AOA, 100 kn - 2022 -2 -2 -1.5 -1.5 -1 -1 Pressure Coefficient -0.5 -0.5 Pressure Coefficient 0 0 0.5 0.5 1 1 1.5 1.5 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 z/c z/c Lower Row -3.5 0° AOA, 207 kn - 2023 -3 C 0° AOA, 200 kn - 2022 -2.5 4° AOA, 207 kn - 2023 4° AOA, 200 kn - 2022 -2 -1.5 -1 -0.5 Pressure Coefficient 0.5 1.5 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 z/c Figure 10.—Pressure coefficient values versus normalized chord length, comparing 2022 and 2023 measurements for AOA = 0 and 4° where the target airspeeds were U = 100, 150, and 200 knots. The corrected airspeeds for tests conducted in 2023 are shown in each graph.

4.5 Stagnation Point Inspection

Figure 11 shows pressure coefficient values plotted against the unwrapped distance ( s ) near the leading edge for AOA sweeps at three airspeeds to identify the stagnation line at the leading edge. The AOA at which the stagnation line occurs at the test article leading edge is plotted as a dashed black curve for each airspeed in Figure 11. This is identified as the curve where C curve is most symmetric about the leading p edge ( s = 0 in.). For the slowest velocity at U = 100.5 knots, the stagnation line occurred at AOA = 0.1°.

For airspeeds of 152.5 and 207 knots, the stagnation line at the leading edge occurred at AOA = 0.3° for both airspeeds. This means for tests runs that were conducted at AOA = 0.0°, the instrumented side of the test article experienced a slightly greater positive pressure. It is not clear what is the cause of the nonaligned flow. It is possible that there is a slight angularity in the flow due to circulation in the closed loop tunnel or that the turntable is not perfectly aligned with the tunnel walls. These positive AOA values are in line with aerodynamic data collected during the 2022 SIDRM tests where the stagnation line was identified to exist at an angle between 0° and 1°. This slight misalignment is not expected to impact ice accretions in any significant manner.

NASA/CR-2026000820 15 100.5 Knots, Lower Row 152.5 Knots, Lower Row -2 -2 -0.4° AoA -0.4° AoA -0.2° AoA -0.2° AoA A B 0.0° AoA 0.0° AoA -1.5 -1.5 0.1° AoA 0.2° AoA 0.2° AoA 0.3° AoA 0.4° AoA 0.4° AoA -1 -1 1.0° AoA 1.0° AoA 2.0° AoA 2.0° AoA 3.0° AoA 3.0° AoA -0.5 -0.5 4.0° AoA 4.0° AoA 0 0 Pressure Coefficient Pressure Coefficient 0.5 0.5 1 1 Non - Instrumented Side Non - Instrumented Side Instrumented Side Instrumented Side ( +AOA = suction) ( +AOA = suction) ( +AOA = pressure) ( +AOA = pressure) 1.5 1.5 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 s (in) s (in) 207.0 Knots, Lower Row -2 -0.4° AoA -0.2° AoA C 0.0° AoA -1.5 0.2° AoA 0.3° AoA 0.4° AoA -1 1.0° AoA 2.0° AoA 3.0° AoA -0.5 4.0° AoA Pressure Coefficient 0.5 Instrumented Side Non - Instrumented Side ( +AOA = pressure) ( +AOA = suction) 1.5 -1 -0.5 0 0.5 1 s (in) Figure 11.—Pressure coefficient values versus unwrapped distance near the leading edge for AOA sweeps at airspeeds of (A) 100.5 knots, (B) 152.5 knots, and (C) 207.0 knots.

5.0 Supercooled Liquid Icing Tests

5.1 Supercooled Liquid Icing Test Objectives and Test Matrix

Supercooled liquid icing tests were conducted as they provide simulation validation data on a 3D geometry. Multiple objectives where set for these ice accretion tests and are listed below.

• Conduct various parameter sweeps ( T , spray duration time, MVD , and AOA ) to measure that parameter’s impact on ice accretion size/mass, location, and characteristics (such as glaze/rime ice and shedding behavior).

• For the T parameter sweep, conduct test runs with 1 °C increments between T = –3 and –6 °C, to 0 0 more closely evaluate the glaze-rime ice transitioning regime.

• For the AOA parameter sweep, conduct a test run at AOA = 0.35°. This is the angle that was preliminarily determined during aerodynamic testing where the stagnation line occurred at the SIDRM leading edge. The ice accretion can be compared to the test run where AOA = 0.0°. After post-processing the data, the stagnation line was determined to be AOA = 0.30° for 152.5 and 207 knots. This is sufficiently close for comparison purposes.

• Conduct rime ice tests allowing for a first order estimate of collection efficiency that can be calculated from rime ice accretion geometry.

NASA/CR-2026000820 16 • Conduct repeat test runs to quantify repeatability.

• Conduct supercooled liquid icing tests that repeat test conditions that were performed during the SIDRM 2022 test entry. Whereas the strut geometry and strut locations were different between the two test entries, and slight differences in U and LWC exist due to the reference pressure issues discussed in Section 3.0, comparisons can provide insight into tunnel repeatability.

Twenty-three supercooled liquid ice accretion test runs were conducted during the 2023 test entry.

Table 3 shows the test conditions (corrected for reference pressure issue) in Columns 1 to 7 and resulting accretion mass in Columns 8 to11. Table 3 is ordered in blocks according to the five parameter sweeps conducted: total air temperature, time duration at rime ice conditions, time duration at glaze ice conditions, MVD , and AOA . Positive AoA values mean that the test article was rotated in the direction that made the instrumented side the pressure side. Unique test runs are identified by their test run ID (i.e., UG no.). In the table, liquid water content is noted as LWC . Drop size distributions for the supercooled liquid clouds used for ice accretion tests are provided in Table A.7 in the Appendix. The static relative humidity is approximated to be saturated at the test section for this atmospheric wind tunnel (i.e., the total pressure is about 1 atm) as an equilibration spray was performed at the start of each day of testing. Four test points were repeated to provide a measure of repeatability (e.g., UG3582 and UG3631 in the total air temperature sweep).

5.2 Testing Procedures—Scanning and Weighing of Ice Mass

The testing procedures for the supercooled liquid ice accretion tests are outlined below.

1. Run up IRT to target test airspeed and air temperature.

2. Start recording data 30 s prior to spray activation.

3. Turn on icing cloud (spray on).

4. Turn off icing cloud per the time specified on the test matrix.

5. Continue holding tunnel airspeed and air temperature constant as data systems continue recording 30 s post spray.

6. Stop data recording systems and shut down drive fan.

7. Enter test section and take photographs of accreted ice.

8. Perform 3D scan of mid 10-in. span of accreted ice.

9. Break off strut ice and place into pan for weighing.

10. Using heated knife, cut out mid 8-in. span of accreted ice on casing and scrape ice into tray for weighing.

11. Remove all ice from SIDRM and clean test article, preparing for next test point.

The primary measurements to assess supercooled liquid ice accretion size were 3D laser scans of the final ice accretion and weighing of the accreted ice. The accreted ice geometry was measured after each test run utilizing a 3D laser scanner. Hexagon’s Romer Absolute SI 7530 scanner was used and has a repeatability accuracy of ± 0.003 in. The center 10-in. (0.25-m) span was scanned from the leading edge to the extent of ice on either side of the test article, including the struts. Figure 12(A) depicts the area that was scanned with resulting 3D image of the ice accretion in the bottom right of the panel. After scanning, ice that had accreted on each of the struts was carefully removed for weighing (Panel (B)). Then the center 8-in. (0.20-m) span of accreted ice on the casing was cut from the leading edge to the extent of icing on both sides, removed, and weighed (Panel (C)). The ice mass measurements for the strut on the instrumented side, the strut on the non-instrumented side, the casing, and the combined total ice mass are provided in Columns 8 to 11 in Table 3.

NASA/CR-2026000820 17 TABLE 3.—TEST CONDITIONS (CORRECTED) FOR DIFFERENT PARAMETER SWEEPS CONDUCTED FOR THE SUPERCOOLED LIQUID ICING TEST RUNS, ALONG WITH FINAL ACCRETED ICE MASS MEASURED AT VARIOUS LOCATIONS Test run conditions Accreted ice mass measurements Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Column 7 Column 8 Column 9 Column 10 Column 11 Test Run, Spray T , U , AOA , MVD , LWC , Instrument side Non-instrument Casing, All ice, ID no. duration, °C knots ° μ m g/m strut, side strut, g g min g g T sweep UG3583 20 –3 152.5 4 25 0.49 180 178.2 415 773.2 UG3584 20 –4 152.5 4 25 0.49 169 190.6 417 776.6 UG3585 20 –5 152.5 4 25 0.49 167.7 182.2 453 802.9 UG3582 20 –6 152.5 4 25 0.49 173.5 190.5 470 834 UG3631 20 –6 152.5 4 25 0.49 156.5 170.9 475 802.4 UG3586 20 –9 152.5 4 25 0.49 172 196 516 884 UG3604 20 –12 152.5 4 25 0.49 172.2 183.3 540 895.5 UG3605 20 –17 152.5 4 25 0.49 172 187.5 583 942.5 Spray duration time sweep—Rime ice UG3587 5 –17 152.5 0 30 0.44 36.8 37.7 189 263.5 UG3619 5 –17 152.5 0 30 0.44 35.8 35.9 189 260.7 UG3588 10 –17 152.5 0 30 0.44 78.8 83.1 392 553.9 UG3613 15 –17 152.5 0 30 0.44 122.2 127.1 545 794.3 Spray duration time sweep—Glaze ice UG3633 5 –6 152.5 4 25 0.49 32.5 34.6 126 193.1 UG3632 10 –6 152.5 4 25 0.49 70.2 73.1 240 383.3 UG3582 20 –6 152.5 4 25 0.49 173.5 190.5 470 834 UG3631 20 –6 152.5 4 25 0.49 156.5 170.9 475 802.4 MVD sweep—Rime ice UG3615 3.5 –17 207 4 18 0.44 28.3 29.1 115 172.4 UG3590 3.5 –17 207 4 30 0.44 34.3 33.3 165 232.6 UG3634 3.5 –17 207 4 30 0.44 33 33.5 161 227.5 UG3608 3.5 –17 207 4 50 0.44 35.8 37.5 245 318.3 UG3607 3.5 –17 207 4 90 0.44 38.7 40.2 315 393.9 UG3635 3.5 –17 207 4 90 0.44 38.9 39.5 332 410.4 AOA sweep—Rime ice UG3589 3.5 –17 207 0 30 0.44 33.6 34.1 181 248.7 UG3616 3.5 –17 207 0.35 30 0.44 34.0 33.5 187 254.5 UG3606 3.5 –17 207 2 30 0.44 33.6 34.2 175 242.8 UG3590 3.5 –17 207 4 30 0.44 34.3 33.3 165 232.6 UG3634 3.5 –17 207 4 30 0.44 33.0 33.5 161 227.5 NASA/CR-2026000820 18 A B Ice on Struts Weighed

Ice on

Struts &

Casing

Weighed

10 in

8 in

Scanned

Ice on Casing Weighed Figure 12.—Images describing (A) the locations that ice was scanned and weighed, with examples showing the process of (B) strut ice being removed for weighing and (C) casing ice being cut ready to be removed into a pan for weighing.

5.3 Total Air Temperature Sweep

A total air temperature sweep was conducted that ranged from glaze to rime ice as T decreased.

Figure 13 shows sample images of a glaze ice accretion conducted at T = –3 °C shown in Panel (A) and a rime ice accretion conducted at T = –17 °C in Panel (B). The accreted ice is partially transparent in the glaze test, and opaque in the rime test case. The insets show the non-instrumented side ice accretion on the struts, where the glaze condition resulted in a horn ice shape, and the rime condition resulting in an aerodynamic pointed ice shape. The total ice mass increased as T decreased as can be seen in the final column of Table 3 for the T sweep. Time lapse video shows continuous shedding of feathers near the ramp top for all test runs, but earlier and more shedding occurred for warmer tests and may account, in part, for the difference in final ice mass that was measured. The greater shedding amounts may be a result of weaker ice cohesion strength compared to colder accretions and feather accretions experiencing more drag due to accretion shape and size. Repeat test runs conducted at T = –6 °C resulted in about 4% difference in total ice mass.

Figure 14 shows cross-sections of the accreted ice at the center-span for the air temperature sweep.

Panel (A) shows the overall view, whereas Panels (B), (C), and (D) show zoomed-in cross sections at the leading edge, instrumented side strut (pressure side), and non-instrumented side strut (suction side), respectively. To avoid repeating descriptions of this figure layout again, each of the remaining subsections in this section (Section 5.0) will have the same figure layout presented. The transition from horn-shaped to streamline shaped ice accretions is evident at the leading edge (Panel (B)) as air temperature decreases, characteristic of the transition from glaze to rime ice. The size of the horn shape reduced as T decreased in 1 °C decrements between T = –3 and –6 °C in Panel (B). The tests were run at AOA = 4°, so the accretions at the leading edge lean towards the pressure side (to the left in Panel (B)). Panels (C) and (D) show evidence NASA/CR-2026000820 19 T = - 17 ° C T = - 3 ° C

0 A B

Run ID# UG3605 Run ID# UG3583 Glaze ice Rime ice Figure 13.—Images of (A) a glaze ice accretion conducted at T = –3 °C and (B) a rime ice accretion conducted at T 0 = –17 °C.

of shadow and concentration regions near the strut junction. Looking at the pressure side (Panel (C)), the shadow region is small and is likely a result of the boundary layer created by the main body upstream of the struts. The shadow and concentration regions of the impinging cloud are more prominent on the suction side (Panel (D)) as the main body at an AoA blocks and impacts cloud flow to the strut downstream at AOA = 4°. The horn ice accretions on the main body leading edge from the warmer test runs appear to have expanded the shadow region on both struts nears the junction. Panel (C) (pressure side) shows that the concentration region for the T = –3 °C test run occurred around y = –4 in., which is further outboard than the T = –17 °C test run which occurred around y = –3.5 in. Similarly, Panel (D) shows that the concentration region for the T = –3 °C test run occurred around y = 6 in., which is further outboard than the T = –17 °C 0 0 which occurred around y = 4.5 in. Of note in Panel (B) is that just aft of the leading edge, there is little to no ice on the casing on the suction side, until just aft of the strut where the casing geometry becomes more exposed to the impinging cloud. Panels (B) and (C) show that there is ice accretion on the pressure side of the casing from the leading edge to the struts.

Figure 15 shows cross-sections of strut leading edge ice accretions at various locations on both struts for the air temperature sweep. Panels (A) and (B) show cuts 3.5 in. from the SIDRM center, near the strut and main body junction (inboard) for the instrumented and non-instrumented side struts, respectively.

Panels (C) and (D) show cuts 8.0 in. from the test article center, further out into the freestream (outboard) for the instrumented and non-instrumented side struts, respectively. A diagram is inset in Panel (B) to provide spatial reference of the four cross-section cuts at the struts. To avoid repeating lengthy descriptions of this figure layout again, each of the remaining subsections in this section (Section 5.0) will have the same figure layout presented. Panels (A) and (B) highlight the impact of shadow regions near the strut junction created by the AOA = 4° test runs with little to no ice accretion on the suction side (Panel (B)). The cross sections in Panel (A) (pressure side) show accretions at the strut junction, which captured ice accretion on the strut leading edge and ice that accreted on the main body. Further outward on the struts, Panels (C) and (D) show the transition from horn-shaped glaze ice to more streamlined rime ice accretions as T decreases.

NASA/CR-2026000820 20 The accretions on the suction side in Panel (D) are larger than on the pressure side in Panel (C). In addition, despite the sizeable shadow region created by the main body at AOA = 4°, accretion mass was greater for the suction side strut than the pressure side strut for all temperatures conducted in the sweep except for T = –3 °C where they were nearly equal (see Columns 8 and 9 from Table 3). This may, but only in part, be a result of how the ice was removed from the struts. For the suction side, the growth and removal of ice from the strut was clear and distinct as there was little to no ice at the strut junction interface as can be seen in Figure 14(D). For the pressure side, there was significant ice growth near the strut junction and therefore there was no clear and distinct cutoff for the strut ice. When the accreted ice on the strut was broken off by hand, the break naturally occurred at its weakest and thinnest point at the junction. An example of the remining ice at the junction can be seen in Figure 12(B). Some measurement variation in strut ice mass will exist where there is ice at the strut junction, in particular for long spray duration tests like these 20-min tests for the T sweep. However, this likely does not fully account for the strut ice mass differences as the suction side accreted ice geometry is noticeably larger than the pressure side for outboard regions of the strut.

Full view cuts at center span, x = 0 in.

Zoom-in of leading-edge cuts at center span, x = 0 in.

To = -3 °C To = -4 °C

B A

To = -5 °C To = -6 °C -5 To = -6 °C 0.5 To = -9 °C To = -12 °C To = -17 °C -10 z (in) z (in) -15 -0.5 -20 -1 -25 -10 -5 0 5 10 -1.5 -1 -0.5 0 0.5 1 1.5 y (in) y (in) Non-Instrumented side strut cuts at center span, x = 0 in.

Instrumented side strut cuts at center span, x = 0 in.

-7 -7 -8 -8

C D

-9 -9 -10 -10 -11 -11 -12 -12 z (in) z (in) -13 -13 -14 -14 -15 -15 -16 -16 2 4 6 8 10 12 -12 -10 -8 -6 -4 -2 y (in) y (in) Figure 14.—Cross-sections of the accreted ice at the center-span for the T sweep. Panel (A) shows the overall view, whereas Panels (B), (C), and (D) show zoomed-in cross sections at the leading edge, pressure side strut, and suction side strut, respectively.

NASA/CR-2026000820 21 y = +3.5 in. cuts (inboard, non-instrumented side strut) y = -3.5 in. cuts (inboard, instrumented side strut) -11 -11 To = -3 °C 8.0 in 3.5 in To = -4 °C - - -11.5 -11.5 y = To = -5 °C y = y = +8.0 in y = +3.5 in To = -6 °C -12 -12 To = -6 °C Instr.

Non - I nstr .

To = -9 °C To = -12 °C -12.5 -12.5 To = -17 °C z (in) z (in) -13 -13 -13.5 -13.5

A B

-14 -14 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 x (in) x (in) y = +8.0 in. cuts (outboard, non-instrumented side strut) y = -8.0 in. cuts (outboard, instrumented side strut) -11 -11 -11.5 -11.5 -12 -12 -12.5 -12.5 z (in) z (in) -13 -13 -13.5 -13.5

D C

-14 -14 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 x (in) x (in) Figure 15.—Cross-sections of strut leading edge ice accretions at inboard (A) and (B) and outboard (C) and (D) locations on both struts for the T 0 sweep.

Multiple test points were repeated from the SIDRM 2022 test entry for the T sweep. Table 4 compares accreted ice mass between the 2023 and 2022 SIDRM test entries. The ice mass from both struts is combined for this comparison. Dashes in the 2022 test entry represent test points that were not conducted or where ice mass not fully measured. As a reminder, due to the reference pressure issue, there are small differences in U and LWC between the two test entries. Airspeed was U = 152.5 knots for 2023 and 3 3 U = 150 knots for 2022. In addition, LWC = 0.49 g/m for 2023, and LWC = 0.50 g/m for 2022. These are small and are not expected to significantly impact overall measurement. An additional reminder is that larger struts were utilized in the 2023 test entry (7-in. chord NACA 0018 for 2023 and 4-in. chord NACA 0012 for 2022). As a result, Table 3 shows that the 50% wider struts from the 2023 tests accreted about 50% more ice compared to the 2022 tests, as the wider struts captured more impinging cloud droplets.

Comparing the accreted ice mass on the casing, approximately 2% lower mass was measured for the 2023 tests, except for the warmest test case. The LWC for 2023 was 2% lower than the 2022 entry, but with the increased airspeed, the overall cloud mass flow rate is constant between the two test entries. It is instead hypothesized that the slightly lower ice mass measurements in 2023 may be due to more droplets that impinged on the larger struts instead of the casing further aft of the struts. The impingement on the casing around the struts is low as the cloud flow is shallow (nearly parallel) with the test article surface geometry, resulting in a small 2% difference between the test entries.

NASA/CR-2026000820 22 TABLE 4.—COMPARISON OF ACCRETED ICE MASS ON THE STRUTS AND CASING BETWEEN THE 2023 AND 2022 SIDRM TEST ENTRIES FOR THE T SWEEP T 0 2023 2022 ° C Ice mass Ice mass Ice mass Ice mass both struts, casing, both struts, casing, g g g g –3 358.2 415 ---- 394 –4 359.6 417 ---- ---- –5 349.9 453 ---- ---- –6 364.0 470 241 479 –6 327.4 475 241 479 –9 368.0 516 239 526 –12 355.5 540 238 551 –17 359.5 583 224 595

5.4 Spray Duration Time Sweep—Rime Ice Conditions

A spray duration time sweep was conducted under rime ice conditions ( T = –17 °C) where spray time ranged from 5 to 15 min. Figure 16 shows sample images of ice accretion for a spray duration of 5 min shown in Panel (A) and 15 min in Panel (B). The accreted ice is opaque for both rime test case. The insets show the instrumented side ice accretion on the struts, where the rime condition resulted in streamlined ice shapes. The total ice mass increased as spray duration time increased as can be seen in Column 11 of Table 3 for this sweep. Time lapse video shows continuous shedding of feathers near the ramp top for tests durations longer than 5 min of accretion. Little to no shedding occurred for the first 5 min. The increase in shedding after 5 min may be a result of larger feather accretions experiencing more drag. The larger feather accretions can be seen for the 15 min spray in Panel (B), whereas the feathers are small and more difficult to see in Panel (A). Repeat test points were conducted at 5 min of spray duration time and resulted in just a 1% difference in total ice mass, suggesting very good repeatability. For reference, these two repeated test runs were conducted 10 days apart.

Figure 17 shows cross-sections of the accreted ice at the center-span for the spray duration time sweep under rime ice conditions. The increase in ice accretion size for longer duration spray times is evident in each panel in Figure 17. The tests were run at AOA = 0°, so the accretions are largely symmetric on all casing surfaces and struts. Symmetric shadow and concentration regions at the struts near the junction can be seen in Panels (C) and (D) due to boundary layer effects along the casing. Figure 17 also shows that ice accreted on both sides of the main body from the leading edge to the struts. The figure shows good repeatability in reproducing the same ice geometry for the 5-min test runs.

NASA/CR-2026000820 23 t = 5 min t = 15 min A B Run ID# UG3619 Run ID# UG3613 260.7 g total 794.3 g total Figure 16.—Images of ice accretions conducted under rime ice conditions after spray durations of (A) t = 5 min and (B) t = 15 min.

Full view cuts at center span, x = 0 in.

Zoom-in of leading-edge cuts at center span, x = 0 in.

0 t = 5 min

B A

t = 5 min t = 10 min 0.5 -5 t = 15 min -10 z (in) z (in) -15 -0.5 -20 -25 -1 -10 -5 0 5 10 -1 -0.5 0 0.5 1 y (in) y (in) Instrumented side strut cuts at center span, x = 0 in. Non-Instrumented side strut cuts at center span, x = 0 in.

-7 -7 -8

-8 D C

-9 -9 -10 -10 -11 -11 -12 -12 z (in) z (in) -13 -13 -14 -14 -15 -15 -16 -16 -12 -10 -8 -6 -4 -2 2 4 6 8 10 12 y (in) y (in) Figure 17.—Cross-sections of the accreted ice at the center-span for the spray time duration sweep under rime ice conditions. Panel (A) shows the overall view, whereas Panels (B), (C), and (D) show zoomed-in cross sections at the leading edge, pressure side strut, and suction side strut, respectively.

NASA/CR-2026000820 24 Figure 18 shows cross-sections of strut leading edge ice accretions at various locations on both struts for the spray duration time sweep under rime ice conditions. Panels (A) and (B) capture cuts in the concentration regions near the strut junction. Panels (C) and (D) show accretions on the struts that are more in the freestream. Of note is how similar the cross-sections of the main body leading edge ice accretions (Figure 17(B)) are to the outboard strut ice accretions (Figure 18(C) and (D)). This is a reasonable result as the leading edge of the main body and struts are of similar size and both locations experienced freestream cloud flow.

Multiple test points were repeated from the SIDRM 2022 test entry for the spray time duration sweep under rime ice conditions. Table 5 compares accreted ice mass between the 2023 and 2022 SIDRM test entries. Again, the wider struts used during the 2023 tests accreted more ice than the thinner struts used in the 2022 test entry, by nearly twice as much. Ice mass on the casing ranged from 4 to 9% lower for the 2023 tests compared to the 2022 test entry. Again, the lower ice mass measurements in 2023 may be due to more droplets that impinged on the larger struts instead of the casing further aft of the struts.

y = -3.5 in. cuts (inboard, instrumented side strut) y = +3.5 in. cuts (inboard, non-instrumented side strut) -11 -11 t = 5 min 3.5 in 8.0 in - - t = 5 min -11.5 -11.5 y = y = y = +8.0 in y = +3.5 in t = 10 min t = 15 min Instr. Non - I nstr .

-12 -12 -12.5 -12.5 z (in) z (in) -13 -13 -13.5 -13.5

B A

C D

-14 -14 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 x (in) x (in) Figure 18.—Cross-sections of strut leading edge ice accretions at inboard (A) and (B) and outboard (C) and (D) locations on both struts for the spray time duration sweep under rime ice conditions.

NASA/CR-2026000820 25 TABLE 5.—COMPARISON OF ACCRETED ICE MASS ON THE STRUTS AND CASING BETWEEN THE 2023 AND 2022 SIDRM TEST ENTRIES FOR THE SPRAY TIME DURATION SWEEP UNDER RIME ICE CONDITIONS Spray 2023 2022 duration, Ice mass Ice mass Ice mass Ice mass min both struts, casing, both struts, casing, g g g g 5 74.5 189 33 208 5 71.7 189 33 208 10 161.9 392 79 407 15 249.3 545 --- ----

5.5 Spray Duration Time Sweep—Glaze Ice Conditions

A spray duration time sweep was conducted under glaze ice conditions ( T = –6 °C) where spray time ranged from 5 to 20 min. Figure 19 shows sample images of ice accretion for a spray duration of 5 min shown in Panel (A) and 20 min in Panel (B). The accreted ice is largely opaque for both glaze tests shown in the figure. The insets show the ice accretion on the instrumented side strut, where the glaze condition resulted in a transitory mix between horn and streamlined ice shapes. As expected, the total ice mass increased as spray duration time increased, as can be seen in Column 11 of Table 3 for this sweep. Time lapse video shows continuous shedding of feathers near the ramp top after about 2 min of accretion.

Shedding for this sweep occurred noticeably sooner in comparison to the 5 min when shedding was observed to begin for the rime ice test runs described in the previous subsection (Section 5.4). This earlier occurrence of shedding may be a result of weaker ice cohesion strength compared to colder accretions.

Repeat test points were conducted at 20 min of spray duration time and resulted in about 4% difference in total ice mass. The difference between the repeated test runs occurred due to differences in ice mass on the struts. For reference, these two repeated test runs were conducted 17 days apart. Note that these two repeat test runs are the same repeated test runs described in the total air temperature sweep of Section 5.3.

Figure 20 shows cross-sections of the accreted ice at the center-span for the spray duration time sweep under glaze ice conditions. The increase in ice accretion size for longer duration spray times is evident and expected in each panel in Figure 20. The figure shows generally good repeatability in reproducing the same ice geometry for the 20-min test runs. The tests were run at AOA = 4°, so the accretions at the leading edge lean towards the pressure side (to the left in Panel (B)). Panels (C) and (D) show evidence of shadow and concentration regions near the strut junction. Looking at the pressure side (Panel (C)), the shadow region is small and is likely a result of the boundary layer created by the main body upstream of the struts. The shadow and concentration regions of the impinging cloud are more prominent on the suction side (Panel (D)) as the main body at an AoA blocks and impacts cloud flow to the strut downstream at AOA = 4°.

The development of horn ice accretions on the main body leading edge for the longer spray duration test runs appear to have expanded the shadow region on both struts nears the junction. The expanded shadow region for longer test runs on the pressure side (Panel (C)) is small, but more prominent on the suction side (Panel (D)). Of note in Panel (B) is that just aft of the leading edge, there is little to no ice on the casing on the suction side, until just aft of the strut where the casing geometry becomes more exposed to the impinging cloud. Panels (B) and (C) show that there is ice accretion on the pressure side of the casing from the leading edge to the struts (and just a bit beyond not shown in the figure).

NASA/CR-2026000820 26 t = 5 min t = 20 min

A B

Run ID# UG3633 Run ID# UG3631 193.1 g total 802.4 g total Figure 19.—Images of ice accretions conducted under glaze ice conditions after spray durations of (A) t = 5 min and (B) t = 15 min.

Full view cuts at center span, x = 0 in.

Zoom-in of leading-edge cuts at center span, x = 0 in.

0 t = 5 min

B A

t = 10 min t = 20 min -5 t = 20 min 0.5 -10 z (in) z (in) -15 -0.5 -20 -1 -25 -1 -0.5 0 0.5 1 -10 -5 0 5 10 y (in) y (in) Instrumented side strut cuts at center span, x = 0 in. Non-Instrumented side strut cuts at center span, x = 0 in.

-7 -7

D C

-8 -8 -9 -9 -10 -10 -11 -11 -12 -12 z (in) z (in) -13 -13 -14 -14 -15 -15 -16 -16 -12 -10 -8 -6 -4 -2 2 4 6 8 10 12 y (in) y (in) Figure 20.—Cross-sections of the accreted ice at the center-span for the spray duration time sweep under glaze ice conditions. Panel (A) shows the overall view, whereas Panels (B), (C), and (D) show zoomed-in cross sections at the leading edge, pressure side strut, and suction side strut, respectively.

NASA/CR-2026000820 27 Figure 21 shows cross-sections of strut leading edge ice accretions at various locations on both struts for the spray duration time sweep under glaze ice conditions. Panels (A) and (B) highlight the impact of shadow regions near the strut junction created by the AOA = 4° test runs with little to no ice accretion on the suction side (Panel (B)). The cross sections in Panel A (pressure side) show accretions at the strut junction, which captured ice accretion on the strut leading edge and ice that accreted on the main body.

Further outward on the struts, Panels (C) and (D) show transitory mix between horn and streamlined ice shapes. The accretions on the suction side in Panel (D) are larger than on the pressure side in Panel (C). In addition, despite the sizeable shadow region created by the main body at AOA = 4°, accretion mass was greater for the suction side strut than the pressure side strut for all accretion times conducted in the sweep (see Columns 8 and 9 from Table 3). It is possible that there is a concentration of the cloud on the suction side when the large test article is at a positive AoA because the flow is more constricted on that side. This would require additional independent measurements and CFD studies to verify this hypothesis.

y = +3.5 in. cuts (inboard, non-instrumented side strut) y = -3.5 in. cuts (inboard, instrumented side strut) -11 -11 t = 5 min t = 10 min 3.5 in 8.0 in - -11.5 -11.5 - t = 20 min y = y = y = +8.0 in y = +3.5 in t = 20 min -12 -12 Instr. Non - I nstr .

-12.5 -12.5 z (in) z (in) -13 -13 -13.5 -13.5

A B

C D

-14 -14 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 x (in) x (in) Figure 21.—Cross-sections of strut leading edge ice accretions at inboard (A) and (B) and outboard (C) and (D) locations on both struts for the spray time duration sweep under glaze ice conditions.

NASA/CR-2026000820 28

5.6 Cloud Median Volumetric Diameter Sweep

A median volumetric diameter ( MVD ) sweep was conducted under rime ice conditions ( T = –17 °C) where MVD ranged from 18 to 90 μm. Figure 22 shows sample images of ice accretions conducted under icing clouds of MVD = 18 μm shown in Panel (A) and MVD = 90 μm in Panel (B). The insets show the non-instrumented side (suction side) ice accretion and highlights the differences in impingement limits between different MVD clouds. This MVD sweep was performed at AOA = 4°, resulting in a shadowed casing on the suction side, with no ice accreting just aft of the leading edge until the casing ramp area near the strut. Larger MVD clouds impinged further upstream into the casing shadow region on the suction side.

Larger MVD clouds also impinged further downstream on the casing ramp beyond the strut, on both the suction and pressure sides. These extended impingement limits are directly related to larger droplets being more ballistic resulting in higher collision efficiencies on SIDRM surfaces, whereas smaller droplets followed the flow more closely and resulted in lower collision efficiencies. The total ice mass increased as MVD increased, as can be seen in Column 11 of Table 3 for this sweep. This increasing ice mass trend with increasing MVD applies entirely on the casing, due to the greater ballistic nature and greater collision efficiency of larger droplets on the various casing surfaces. The ice mass was approximately equal between the struts, despite tests performed at AOA = 4°. Time lapse video shows less shedding for larger MVD clouds. No shedding was observed for tests with MVD of 50 μm and greater for these 3.5-min duration accretion tests. Two sets of repeat test points were conducted at MVD = 30 and 90 μm, which resulted in about 2% to 4% difference in total ice mass. For reference, these two repeated test runs were conducted 15 and 9 days apart, respectively.

Figure 23 shows cross-sections of the accreted ice at the center-span for the MVD sweep. The ice accretion leading edge thickness increased slightly with increasing MVD (Panel (B)). This was likely due to larger drops resulting in greater collision efficiencies at this leading edge for the MVD values tested.

Panel (C) shows that large MVD test runs resulted in thicker ice accretions along the pressure side casing.

The majority of increase in total ice mass with increasing MVD occurred on the casing, with smaller contributions coming from the struts. This is in agreement with what is shown in Panels (C) and (D). The figure shows good repeatability in reproducing the same ice geometry for the two repeat test runs. The tests were run at AOA = 4°, so the accretions at the leading edge lean towards the pressure side (to the left in Panel (B)). Panels (C) and (D) show evidence of shadow and concentration regions near the strut junction.

MVD = 18 μm MVD = 90 μm

A B

Run ID# UG3615 Run ID# UG3607 172.4 g total 393.9 g total Figure 22.—Images of ice accretions conducted under icing clouds with (A) MVD = 18 μm and (B) MVD = 90 μm.

NASA/CR-2026000820 29 Full view cuts at center span, x = 0 in.

Zoom-in of leading-edge cuts at center span, x = 0 in.

0 MVD = 18 m MVD = 30 m

B A

MVD = 30 m -5 MVD = 50 m 0.5 MVD = 90 m MVD = 90 m -10 z (in) z (in) -15 -0.5 -20 -1 -25 -10 -5 0 5 10 -1 -0.5 0 0.5 1 y (in) y (in) Instrumented side strut cuts at center span, x = 0 in. Non-Instrumented side strut cuts at center span, x = 0 in.

-11 -11

D C

-11.5 -11.5 -12 -12 z (in) z (in) -12.5 -12.5 -13 -13 -13.5 -13.5 -5.5 -5 -4.5 -4 -3.5 -3 -2.5 2.5 3 3.5 4 4.5 5 5.5 y (in) y (in) Figure 23.—Cross-sections of the accreted ice at the center-span for the MVD sweep. Panel (A) shows the overall view, whereas Panels (B), (C), and (D) show zoomed-in cross sections at the leading edge, pressure side strut, and suction side strut, respectively.

Looking at the pressure side (Panel (C)), the shadow region is small and is likely a result of the boundary layer created by the main body upstream of the struts. The shadow and concentration regions of the impinging cloud are more prominent on the suction side (Panel (D)) as the main body at an AoA blocks and impacts cloud flow to the strut downstream at AOA = 4°. Looking at the strut on the suction side (Panel (D)), the severity of shadowing is less prominent for larger MVD clouds. Again, this is due to larger droplets being more ballistic than smaller droplets. The cross sections in Panel (B) shows that there is no ice on the suction side casing from just aft of the leading edge to around the strut area (Panel (D)). While it is small, Panel (D) reinforces the statement in the previous paragraph where the impingement limit on the suction side casing is further upstream for larger MVD clouds.

Figure 24 shows cross-sections of strut leading edge ice accretions at various locations on both struts for the MVD sweep. Panel (A) shows cross sections on the edge of the concentration region at the inboard cut on the pressure side strut, with slightly larger accretions for larger MVD clouds. Panel (B) shows cross sections in the shadowed region on the suction side strut, reinforcing the reduced impact of shadowing of larger MVD ballistic droplets. Panels (C) and (D) show essentially no variation in strut leading edge ice NASA/CR-2026000820 30 accretion size and geometry for the various MVD test runs. This low sensitivity to MVD may be due to similar collision efficiencies on the narrow struts for all MVD tested.

5.7 Angle of Attack Sweep

An AOA sweep was conducted under rime ice conditions ( T = –17°C) where AOA ranged from 0 to 4°. Figure 25 shows sample images of ice accretions conducted at AOA = 0° shown in Panel (A) and AOA = 4° in Panel (B). The insets show the overhead view of the non-instrumented side strut (suction side when AOA > 0°). The insets show the ice accretion profile at the strut leading edge. Note that ice only accreted on the strut leading edge, and any white surfaces seen aft of the leading edge is white titanium dioxide paint used for 3D laser scanning that was not fully removed from the strut. The strut ice accretion profiles in the insets highlight the shadow and concentration regions that resulted when the test article was rotated for the 4° AOA test run. The test run performed at AOA = 4° (Panel (B)), resulted in a shadowed casing on the suction side, with no ice accreting just aft of the leading edge until the casing ramp area near the strut. Whereas ice accreted on all forward surfaces of the main body for the test run performed at AOA = 0° (Panel (A)). As a result, ice mass largely decreased with increasing AOA , as can be seen in Column 11 y = +3.5 in. cuts (inboard, non-instrumented side strut) y = -3.5 in. cuts (inboard, instrumented side strut) -11 -11 MVD = 18 m 3.5 in MVD = 30 m 8.0 in - - -11.5 -11.5 MVD = 30 m y = y = y = +8.0 in y = +3.5 in MVD = 50 m -12 -12 MVD = 90 m Instr. Non - I nstr .

MVD = 90 m -12.5 -12.5 z (in) z (in) -13 -13 -13.5 -13.5

A

B

C

D

-14 -14 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 x (in) x (in) Figure 24.—Cross-sections of strut leading edge ice accretions at inboard (A) and (B) and outboard (C) and (D) locations on both struts for the MVD sweep.

NASA/CR-2026000820 31 of Table 3 for this sweep. This trend is due to more main body surfaces that experienced increased shadowing from the cloud at greater angles of attack. A test run was performed at AOA = 0.35°, the angle that was preliminarily determined after aerodynamic testing to be where the stagnation line occurred at the leading edge (this was determined to be AOA = 0.30° after post-processing as noted in Section 4.5). There was 3% more ice mass measured for this AOA = 0.35° compared to the AOA = 0.0° test run. For reference, the repeat test runs in this sweep varied by 2%. This suggests that differences between the AOA = 0.0 and 0.35° test runs are similar to the testing variation noise and the impact is small. The ice mass was approximately equal between the struts for all angles of attack tested for this sweep (see Table 3, Columns 8 and 9). Time lapse video showed very little shedding for these 3.5-min duration accretion tests.

Figure 26 shows cross-sections of the accreted ice at the center-span for the AOA sweep. Panel (B) shows how the accreted ice at the main body leading edge shifts to the pressure side as AOA increased.

Panels (B), (C), and (D) show how the casing ice is symmetric for the AOA = 0.0 and 0.35° test runs, but as AOA increased, more ice accreted on the pressure side casing (Panel (C)), and shadowing effects became more significant on the suction side casing (Panel (D)). Panels (C) and (D) show evidence of shadow and concentration regions on the strut near the junction. Looking at the pressure side (Panel (C)), the shadow region is small due to the boundary layer created by the main body upstream of the struts and became smaller as AOA increased. The shadow and concentration regions of the impinging cloud are more prominent on the suction side (Panel (D)) as the main body blocked more of the impinging cloud as AOA increased. Of note, the cross section accretions are very similar for the AOA = 0.0 and 0.35° test runs in all panels of Figure 26, highlighting the small impact the deviation of the true aerodynamic stagnation line at the leading edge has on the overall ice accretion.

Figure 27 shows cross-sections of strut leading edge ice accretions at various locations on both struts for the AOA sweep. Panels (A) and (B) show variation in cross section geometry as these inboard cuts are taken in the shadow and concentration regions on the struts. Panels (C) and (D) show essentially no variation in strut leading edge ice accretion size and geometry for the various AOA test runs, and little to none was expected as changing AOA does little to impact collision efficiency in the outboard sections of the struts that are exposed to the free stream.

AOA = 0 ° AOA = 4 °

A B

Run ID# UG3589 Run ID# UG3634

248.7 g total 227.5 g total

Forward Forward

Aft

Figure 25.—Images of ice accretions conducted at (A) AOA = 0° and (B) AOA = 4° showing impacts of shadowing effects.

NASA/CR-2026000820 32 Full view cuts at center span, x = 0 in.

Zoom-in of leading-edge cuts at center span, x = 0 in.

AOA = 0.0°

B A

AOA = 0.35° AOA = 2.0° -5 AOA = 4.0° 0.5 AOA = 4.0° -10 z (in) z (in) -15 -0.5 -20 -1 -25 -10 -5 0 5 10 -1 -0.5 0 0.5 1 y (in) y (in) Instrumented side strut cuts at center span, x = 0 in. Non-Instrumented side strut cuts at center span, x = 0 in.

-11 -11

D C

-11.5 -11.5 -12 -12 z (in) z (in) -12.5 -12.5 -13 -13 -13.5 -13.5 -5.5 -5 -4.5 -4 -3.5 -3 -2.5 2.5 3 3.5 4 4.5 5 5.5 y (in) y (in) Figure 26.—Cross-sections of the accreted ice at the center-span for the AOA sweep. Panel (A) shows the overall view, whereas Panels (B), (C), and (D) show zoomed-in cross sections at the leading edge, pressure side strut, and suction side strut, respectively.

NASA/CR-2026000820 33 y = +3.5 in. cuts (inboard, non-instrumented side strut) y = -3.5 in. cuts (inboard, instrumented side strut) -11 -11 AOA = 0.0° 8.0 in 3.5 in - - AOA = 0.35° -11.5 -11.5 y = y = y = +8.0 in y = +3.5 in AOA = 2.0° AOA = 4.0° -12 -12 AOA = 4.0° Instr.

Non - I nstr .

-12.5 -12.5 z (in) z (in) -13 -13 -13.5 -13.5

A B

C D

-14 -14 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 x (in) x (in) Figure 27.—Cross-sections of strut leading edge ice accretions at inboard ((A) and (B)) and outboard ((C) and (D)) locations on both struts for the AOA sweep.

NASA/CR-2026000820 34

6.0 Ice Crystal Icing Tests

6.1 Ice Crystal Icing Test Objectives and Test Matrix

Multiple objectives where set for these ice crystal icing (ICI) tests and are listed below.

• Evaluate impact of larger and shifted forward struts on ice accretion around the strut junction.

• Conduct ICI tests that repeat test conditions that were performed during the SIDRM 2022 test entry.

Whereas differences exist in U and IWC due to the reference pressure issues discussed in Section 3.0, comparisons can provide insight on repeatability and impact of the new struts.

• Conduct tests evaluating impact of heater surface heat flux on ice accretion.

• Conduct parameter sweeps where all other test conditions, including heater settings, are fixed to measure that parameter’s impact on ice accretion size/mass, location, and characteristics (such as shedding and ice growth features). The initial 2022 test entry was more exploratory in nature and heater settings were varied within those parameter sweeps.

• Conduct repeat test runs to quantify repeatability.

Twenty-one ice crystal icing tests are presented here from the 2023 test entry. Table 6 shows the test conditions in Columns 1 to 7, heat flux settings for the six SIDRM heater sections in Columns 8 to 13, and resulting accretion mass in Columns 14 to 17. Table 6 is ordered in blocks according to different test objectives. Shaded orange cells indicate condition or heater setting that varied for that test objective block.

Three test points were repeated to provide a measure of repeatability (e.g., UG3594 and UG3626 in the second test objective block). The airspeed is corrected for the reference pressure issue. No correction is provided for the ice water content ( IWC ). The IWC values listed in Table 6 are from ice crystal cloud characterization tests conducted during the 2022 test entry (Ref. 35). The IWC that was measured in 2022 was a combination of the glaciated icing cloud that was directly injected into the test section from the spray bars (freezeout of sprayed liquid droplets) and recirculation of the glaciated icing cloud within the closed- loop wind tunnel. Looking at the direct spray bar contribution to IWC , the correction is within 1% from the intended water content for the conditions sprayed. The recirculating component is estimated to be impacted by this amount as well. This total correction amount falls within the variation noise measured for IWC during the 2022 characterization tests, which was around 10%. For this reason, no IWC corrections were made. The MVD values listed in Table 6 are also from ice crystal cloud characterization tests conducted during the 2022 test entry. Particle size distributions for the ice crystal clouds used for ice accretion tests are provided in Table A.8 in the Appendix. Again, the static relative humidity is approximated to be saturated at the test section for this atmospheric wind tunnel as an equilibration spray was performed at the start of each day of testing, which introduced humidity to the flowing air.

Power supply controllers provided power to the six heating zones, where each of the six zones was controlled independently. For Zone 1 that was heated by a cartridge heater, the heat flux values were calculated using the power as measured by the power supply controller divided by the full surface area of a cylinder with a 0.47-in. radius, an approximation for the outer mold line geometry of the leading edge.

For Zones 2 to 6, heat flux values were calculated using the power as measured by the power supply controller to each zone and divided by the thin film resistive heating element footprint. All heat generated by the heaters was approximated to be transferred outward toward the outer mold line of the test article, as the side of the heater facing away from the outer mold line was lined with several layers of insulation.

NASA/CR-2026000820 35 NASA/CR-2026000820 TABLE 6.—TEST CONDITIONS AND HEATER SETTINGS FOR THE ICE CRYSTAL ICING TESTS, GROUPED BY TEST OBJECTIVE WITH ACCRETED ICE MASS THAT WAS MEASURED [Shaded orange cells indicate condition or heater setting that varied for that test objective block.]

Test run conditions Heater settings Accreted ice mass measurements Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Column 7 Column 8 Column 9 Column 10 Column 11 Column 12 Column 13 Column 14 Column 15 Column 16 Column 17 Test run, Spray T , U , AOA , MVD , IWC , Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Instrument Non-instrument Leading Ice mass no. duration, °C knots ° μm g/m flux, flux, flux, flux, flux, flux, casing, casing, edge, total, 2 2 2 2 2 2 min W/in W/in W/in W/in W/in W/in g g g g Block 1: Repeat of 2022 Test Conditions at T = –15 °C UG3596 10.0 –15 152.5 0 27 1.9 7.1 2.8 3.3 3.2 6.3 4.0 17 18 --- 35 UG3592 10.0 –15 152.5 2 27 1.9 7.1 2.8 2.7 3.2 6.3 4.0 26 7 --- 33 UG3581 10.0 –15 152.5 4 27 1.9 7.1 2.3 2.5 3.2 6.3 4.0 18 --------------- 17 35 Block 2: Repeat of 2022 test conditions at T = –20 °C UG3599 10.0 –20 152.5 0 26 2.2 8.9 3.6 4.2 4.0 7.9 4.6 22 16 --- 38 UG3595 10.0 –20 152.5 2 26 2.2 8.9 3.6 3.3 4.0 7.9 4.6 26 Not weighed --- 26 UG3594 10.0 –20 152.5 4 26 2.2 8.9 3.1 3.3 4.0 7.9 4.6 17 --------------- 17 34 UG3626 10.0 –20 152.5 4 26 2.2 8.9 3.1 3.3 4.0 7.9 4.6 12.5 --------------- 10.4 22.9 Block 3: Heater surface heat flux evaluation UG3629 10.0 –20 152.5 4 26 2.2 7.1 3.1 3.3 4.4 7.5 5.3 17.1 --------------- 10.1 27.2 UG3627 10.0 –20 152.5 4 26 2.2 9.9 3.1 3.3 4.4 7.5 5.3 28.2 --------------- 27.6 55.8 UG3637 10.0 –20 152.5 4 26 2.2 12.0 3.1 3.3 4.4 7.5 5.3 46.4 28.2 74.6 UG3630 10.0 –20 152.5 4 26 2.2 12.0 3.6 3.9 4.4 7.5 5.3 28.3 9.7 --- 38 Block 4: Spray Duration Time Sweep UG3622 5.0 –20 152.5 0 41 3.0 16.7 3.9 4.2 6.1 7.5 5.3 11.8 13 --- 24.8 UG3624 10.0 –20 152.5 0 41 3.0 16.7 3.9 4.2 6.1 7.5 5.3 31.6 33.9 --- 65.5 Block 5: AOA sweep at T = –15 °C and U = 207 knots UG3600 10.0 –15 207 0 28 2.0 9.9 3.1 3.3 4.4 7.5 5.3 ---- 3.5 --- 3.5 UG3601 10.0 –15 207 2 28 2.0 9.9 3.1 3.3 4.4 7.5 5.3 4.2 --------------- --- 4.2 UG3597 10.0 –15 207 4 28 2.0 9.9 3.1 3.3 4.4 7.5 5.3 11 --------------- 8 19 UG3623 10.0 –15 207 4 28 2.0 9.9 3.1 3.3 4.4 7.5 5.3 13.6 --------------- 6.5 20.1 Block 6: AOA sweep at T = –20 °C and U = 152.5 knots UG3611 5.0 –20 152.5 0 41 3.0 9.9 3.1 3.3 4.4 7.5 5.3 1.2 1.4 --- 2.6 UG3610 5.0 –20 152.5 2 41 3.0 9.9 3.1 3.3 4.4 7.5 5.3 8.1 --------------- 2.9 11.0 UG3609 5.0 –20 152.5 4 41 3.0 9.9 3.1 3.3 4.4 7.5 5.3 13.6 --------------- 6.6 20.2 UG3636 5.0 –20 152.5 4 41 3.0 9.9 3.1 3.3 4.4 7.5 5.3 11.8 --------------- 5.8 17.6 For reference, the steady state surface temperature prior to spray activation is provided in Table A.9 in the appendix. The measurements listed provide additional insight into the resulting temperatures for the given aerothermal test conditions and heater settings per individual test run.

A key requirement for the ice crystal icing tests was to generate accretions without shedding ice or limit the amount of shedding. This was desired so the scanning and weighing of the accreted ice at the end of a test run would represent the entire accretion process. Conditions that produced ice but had one or more significant sheds provided less valuable quantitative data.

6.2 Testing Procedures—Scanning and Weighing of Ice Mass

The testing procedures for the ice crystal accretion tests are outlined below.

1. Run up IRT to target test airspeed and air temperature.

2. Activate SIDRM heaters to target heat flux values and wait until thermocouples read steady values.

3. Start recording data 30 s prior to spray activation.

4. Turn on ice crystal cloud (spray on).

5. Turn off ice crystal cloud per the time specified on the test matrix (SIDRM heaters turned off simultaneously with spray off).

6. Continue holding tunnel airspeed and air temperature constant as data systems continue recording 30 s post spray.

7. Stop data recording systems and shut down drive fan.

8. Enter test section and take photographs of accreted ice.

9. Perform 3D scan of mid 10-in. span of accreted ice.

10. Using heated knife, cut out mid 8-in. span of accreted ice on casing and scrape ice into tray for weighing.

11. Remove all ice from SIDRM and clean test article, preparing for next test point.

The primary measurements to assess ice crystal ice accretion size were 3D laser scans of the final ice accretion and weighing of the accreted ice. As discussed in the supercooled liquid icing sections, the accreted ice geometry was measured after each test run utilizing a 3D laser scanner. The center 10-in.

(0.25-m) span was scanned from the leading edge to the extent of ice on either side of the test article. After scanning, the center 8-in. (0.20-m) span of accreted ice on the casing was cut from the leading edge to the extent of icing on both sides, removed, and weighed. Ice generally accreted on the main body casing in three isolated areas, and they were weighed separately. Figure 28 shows the locations where ice was removed and weighed on the instrumented side casing (yellow box in Panel (A)), the leading edge (sum of green boxes in Panels (A) and (B)), and the non-instrumented side casing (red box in Panel (C)). The instrumented side casing ice mass, non-instrumented side casing ice mass, leading edge ice mass, and the combined total ice mass are provided in Columns 14 to 17, respectively, in Table 6.

Ice crystal icing accretions were generally small as can be seen in Figure 28. Due to the shallow ice accretion geometry, this report will show photos of the accreted ice as they are easier to visualize and are more informative than the cross section from the laser scans.

NASA/CR-2026000820 37 Yellow box: ice mass on instrumented side casing Sum of the green boxes: Ice mass on leading edge Red box: ice mass on non - instrumented side casing A B C

8 in

Flow

Instrumented Side Non - Instrumented Side Non - Instrumented Side Figure 28.—Images indicating the locations that ice was removed and weighed (A) on the instrumented side casing, (A and B) the leading edge, and (C) the non-instrumented side casing.

6.3 Block 1: Repeat of 2022 Test Conditions at T = –15 °C

Three test points were repeated from the SIDRM 2022 test entry where T = –15 °C (Block 1 of Table 6). There are small differences in heat flux for heating Zones 2 and 3 between the three test points.

The AoA varied for where AOA = 0, 2 and 4°. As a reminder, due to the reference pressure issue, airspeed was U = 152.5 knots for 2023 and U = 150 knots for 2022. Whereas this is a small airspeed difference, it was recognized that the steady state SIDRM surface temperatures prior to icing cloud activation were 0.5 to 1.0 °C lower during 2023 testing compared to the 2022 tests, for the same heater setting. The slightly greater airspeed in 2023 may have accounted for this surface temperature difference.

Figure 29 shows ice accretions on the instrumented side, comparing 2023 test runs (Panels (A) to (C)) to 2022 test runs (Panels (D) to (F)). The corresponding repeated test conditions between the 2023 and 2022 tests are indicated with red double-sided arrows. Overall, the location and physical appearance of ice accretions were similar between the repeated test conditions. For, the AOA = 0° test runs (Panels (A) and (D)), the ice only accreted at the ramp base and appeared like frozen runback and amorphous in appearance.

Not shown in the figure, ice accreted similarly on the non-instrumented side for these AOA = 0° test runs.

For the AOA = 4° test runs (Panels (C) and (F)), ice at first accreted at the ramp base, then around the leading edge later into the test. The accreted ice was more orderly with shark teeth features at AOA = 4°. It is worth noting that shark teeth-like ice accretion features were also observed during the full-scale engine icing tests conducted at GRC (Refs. 29 and 30), suggesting that some basic icing physics were replicated with this component-level test article. More ice is visible for the 2022 test run. No ice accreted on the non- instrumented side (suction side) ramp base for these AOA = 4° test runs.

NASA/CR-2026000820 38 Run# UG3596 Run# UG3592 Run# UG3581 AOA = 0 ° AOA = 2 ° AOA = 4 °

Flow

A B C Run# UG3561 Run# UG3560 Run# UG3563 AOA = 2 ° AOA = 0 ° AOA = 4 ° D E F Figure 29.—Images of instrumented side ice accretions comparing 2023 test runs (A) to (C) to 2022 test runs (D) to (F). The corresponding repeated test conditions between the 2023 and 2022 tests are indicated with red double-sided arrows.

The 2022 tests utilized struts that were NACA 0012 in geometry and 4 in. in chord length. Panels (D) to (F) of Figure 29 show how all the ice accreted at the ramp base, just upstream of the strut. These struts did not impact ice crystal ice accretions. The 2023 tests utilized larger struts (NACA 0018 geometry, 7-in. chord) and were also pushed forward 3 in. into the ramp base on the casing. There were expectations that these modified struts would impact ice accretion, with struts acting as a physical anchoring point where more ice would accrete around the strut-casing junction. Panels (A) to (C)of Figure 29 show that this was not the case for this test block. The strut generally displaced ice that had accreted in that location in the 2022 tests. Panels (A) and (B) of Figure 29 show a boundary region around the strut where ice did not accrete. It is not clear if this was due to aerodynamic impacts of the larger strut deflecting impinging ice crystals from the area on the casing around the strut junction, or if it was a thermal impact of the solid unheated strut that cooled the casing around the strut junction to temperatures not suitable for accreting ice.

Table 7 compares accreted ice mass between the 2023 and 2022 SIDRM test entries. The ice mass on the instrumented side casing, non-instrumented side casing, and leading edge for the 2023 and 2022 SIDRM test entries are provided in Columns 2 to 4 and 6 to 8, respectively. Dashes indicates that ice did not accrete in that region. Table 7 shows that less ice accreted on the casing for the 2023 test runs. In part, the 2023 lower ice mass values on the casing may be due to the larger strut displacing ice that had accreted in that location in the 2022 tests. In addition, the slightly higher airspeed tested in 2023 reduced surface temperatures a small amount, where small changes in the overall thermal balance at the surface can critically impact overall ice accretion.

NASA/CR-2026000820 39 TABLE 7.—COMPARISON OF ACCRETED ICE MASS ON THE INSTRUMENTED SIDE CASING, NON-INSTRUMENTED SIDE CASING, AND LEADING EDGE BETWEEN THE 2023 AND 2022 SIDRM TEST ENTRIES FOR TEST CONDITIONS WHERE T = –15 °C 2023 2022 Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Column 7 Column 8 AOA , Test run, Instrument Non-instrument Leading Test run, Instrument Non-instrument Leading ° no. casing, casing, edge, no. casing, casing, edge, g g g g g g 0 UG3596 17 18 -- UG3560 30 33 -- 2 UG3592 26 7 -- UG3561 39 11 -- 4 UG3581 18 -- 17 UG3563 24 -- 16

6.4 Block 2: Repeat of 2022 Test Conditions at T = –20 °C

Three test points were repeated from the SIDRM 2022 test entry where T = –20 °C (Block 2 of Table 6). There are small differences in heat flux for heating Zones 2 and 3 between the test points. The AoA varied where AOA = 0, 2 and 4°. The AOA = 4° test condition was repeated in 2023 (i.e., two test runs in 2023, and one test run in 2022 for the AOA = 4° test condition). Like with the previous subsection, due to the reference pressure issue, airspeed was U = 152.5 knots for 2023 and U = 150 knots for 2022.

Figure 30 shows ice accretions on the instrumented side, comparing 2023 test runs (Panels (A) to (D)) to 2022 test runs (Panels (E) to (G)). The corresponding repeated test conditions between the 2023 and 2022 tests are indicated with red double-sided arrows. The two test runs at AOA = 4° in 2023 are shown in Panels (C) and (D), whereas the corresponding repeated test run in 2022 is shown in Panel (G). Overall, the location and physical appearance of ice accretions are similar between the repeated test conditions. For, the AOA = 0° test runs (Panels (A) and (E)), the ice only accreted at the ramp base and its form was amorphous in appearance. For the AOA = 4° test runs (Panels (C)/(D) and (F)), ice at first accreted at the ramp base, then around the leading edge later into the test. The ice accreted as more orderly with shark teeth features at AOA = 4°. Some variation in amounts of accreted ice is noticeable between the three test runs at AOA = 4°.

Table 8 compares accreted ice mass between the 2023 and 2022 SIDRM test entries. The ice mass on the instrumented side casing, non-instrumented side casing, and leading edge for the 2023 and 2022 SIDRM test entries are provided in Columns 2 to 4 and 6 to 8, respectively. Table 8 shows that less ice mass was measured on both sides on the casing for the AOA = 0° test run in 2023. Figure 30 suggests that this may be due to the larger strut displacing ice that had accreted in that location in the 2022 tests.

Table 8 shows that similar ice mass was measured on the instrumented side casing for the AOA = 2° test runs between the years. Ice had accreted on the non-instrumented side casing (not shown in this report) in the 2023 test run but was not weighed. The two test runs conducted in 2023 at AOA = 4° shows the variability that can occur between repeat test runs just 14 days apart. The ice mass measured during the 2022 test series falls between the values measured during the two 2023 tests.

NASA/CR-2026000820 40 Run# UG3599 Run# UG3595 Run# UG3594 Run# UG3626 AOA = 0 ° AOA = 2 ° AOA = 4 ° AOA = 4 °

Flow

A B C D Run# UG353 Run# UG357 Run# UG3559 AOA = 0 ° AOA = 2 ° AOA = 4 ° E F G Figure 30.—Images of ice accretions comparing 2023 test runs ((A) to (D)) to 2022 test runs ((E) to (G)). The corresponding repeated test conditions between the 2023 and 2022 test are indicated with red double-sided arrows.

TABLE 8.—COMPARISON OF ACCRETED ICE MASS ON THE INSTRUMENTED SIDE CASING, NON-INSTRUMENTED SIDE CASING, AND LEADING EDGE BETWEEN THE 2023 AND 2022 SIDRM TEST ENTRIES FOR TEST CONDITIONS WHERE T = –20 °C 2023 2022 Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Column 7 Column 8 AOA , Test run, Instrument Non-instrument Leading Test run, Instrument Non-instrument Leading ° no. casing, casing, edge, no. casing, casing, edge, g g g g g g 0 UG3599 22 16 ----- UG3553 32 33 --- 2 UG3595 26 Not weighed ----- UG3557 23 10 --- 4 UG3594 17 ---------------- 17 UG3559 18 --- 14 4 UG3626 12.5 ---------------- 10.4

6.5 Block 3: Heater Surface Heat Flux Evaluation

A series of test runs were conducted to evaluate the impact of heat flux on ice accretion (Block 3 of Table 6). Figure 31 illustrates the impact of heat flux on accreted ice mass and location. Heat flux for Zones 1 to 3 varied, with all other test conditions held constant. The shorthand “low”, “medium”, “optimized”, and “high” are used to describe the heater settings used for Zones 1 to 3, and are shown in Panels (A) to (D), respectively. Panel A shows ice accretion that resulted from a test run conducted at the low heat flux NASA/CR-2026000820 41 A D B C Flow Run# UG3629 Run# UG3630 Run# UG3637 Run# UG3627 Low heater setting High heater setting Optimized heater setting Medium heater setting Total ice = 27.2 g Total ice = 38 g Total ice = 74.6 g Total ice = 55.8 g Figure 31.—End of test run images showing the resulting ice accretion at (A) low, (B), medium, (C), optimizes, and (D) high heater settings in terms of accreting ice.

setting, which resulted in the lowest total accreted ice mass. The leading edge became iced about 8 min into the test run limiting the supply of runback melt to the ramp base where impinging ice crystals are better captured by the liquid melt. The leading edge (Zone 1) heat flux was increased for the test run shown in Panel (B), which shows a greater amount of ice that accreted. The warmer leading edge generated more runback melt that captured more of the impinging ice crystals at the ramp base. The leading edge became fully iced near the end of the 10 min test run. The leading edge heat flux was increased even higher for the test run shown in Panel (C). This heater setting resulted in the greatest total accretion ice mass, and for this reason this heater setting is considered optimized for this test block. The higher heat flux for Zone 1 kept the region near the leading edge sufficiently warm that it did not freeze, which provided a continues supply of liquid melt to the ramp base throughout the duration of the test runs. The continuous supply of liquid melt at the ramp base aided in the capture/sticking of impinging ice particles at this higher collision efficiency area of the ramp, resulting in the greatest accretion mass. Panel (D) shows ice accretions resulting from a test run conducted at high heater settings, which resulted in repeated build and shed events throughout the test run. The total accreted ice mass weighed after the test run was lower than others in this test block, however with the continuous build and sheds that occurred throughout the test run, it may have accreted more ice overall but the ice that had shed could not be measured. These test runs demonstrate how upstream heat sources that supply liquid melt to critical regions downstream can lead to larger ice accretions. For reference, Table A.9 in the Appendix lists steady state surface temperatures prior to spray activation and shows how temperatures climbed higher for higher heater settings for this sweep. The ice accretion was orderly with shark teeth features for the first three test runs (Panels (A) to (C)), but was a mixture of order and amorphous disorder for the high heater setting (Panel (D)) from the significant amount of runback melt that was generated and frozen.

6.6 Block 4: Spray Duration Time Sweep

Two test runs were conducted to evaluate the impact of spray duration time (Block 4 of Table 6).

Figure 32 shows the resulting ice accretions conducted for 5 min of spray duration time in Panel (A) and 10 min of spray duration time in Panel (B). These were two separate tests that started with a clean test article (i.e., not a continuation of the 5-min spray). The inset in Panel (B) shows the ice accretion midway into the 10-min spray to compare with the 5-min test run. Comparing the two test runs at 5 min, the ice NASA/CR-2026000820 42 accretion location and size are similar, indicating good repeatability. The 10-min run resulted in a greater accretion size and more than twice the ice mass as ice accreted throughout the test run (see Table 6, Column 17) . It should be noted that the leading edge is clear of ice and was able to provide a continuous supply of liquid melt to the ramp base around the strut. For reference, of all test runs presented in this report, these tests used the highest heat flux setting for Zones 1 to 4 (the forward half of the SIDRM test article where all icing occurred). These test runs demonstrate how engines exposed to ice crystal clouds for longer durations can result in greater amounts of ice accretions if engine surfaces are sufficiently warm and provide a continuous heat supply.

These tests showed that the strut had some impact on the ice accretion. Ice began accreting around the strut at the start of the test run and slowly grew further out in the span and axial directions. The regions lateral to the strut were largely clear of ice after 5 min, suggesting that without the strut presence, ice would not have accreted. There are three factors that may have contributed to the ice accretion near the strut. The first is the strut’s physical presence which could have acted as a backstop for some of the runback melt and impinging ice crystal cloud. Secondly, the solid unheated strut may have aided cooling locally on the main body by acting like a fin heatsink. The runback melt with impinging ice crystal cloud may have been cooled down enough to freezing temperatures and began accreting around the strut. Finally, there is a hole in the thin film heater under the struts as there is structural support on the underside of the main body under the strut. This will naturally result in cooler surface temperatures locally around the strut. Despite this heater “dead zone” under the strut, it did not seem to impact accretion for most of the other tests, as most other tests resulted in more uniform accretions across the span. The ice accretions in both test runs were amorphous in appearance.

Run# UG3622 Run# UG3624

A

B

5 min 10 min Total ice = 24.8 g Total ice = 65.5 g

Flow

(5 min)

Figure 32.—End of test run images showing the resulting ice accretion for spray duration times of (A) 5 min and (B) 10 min, with inset showing accretion midway into the 10-min spray for comparison.

NASA/CR-2026000820 43 A D C B Flow Flow Run# UG3600 Run# UG3601 Run# UG3597 Run# UG3623 AOA = 0 ° AOA = 2 ° AOA = 4 ° AOA = 4 ° (repeat) Total ice = 3.5 g Total ice = 4.2 g Total ice = 19.0 g Total ice = 20.1 g No Sharkteeth Limited Sharkteeth Sharkteeth Sharkteeth Figure 33.—End of test run images showing the resulting ice accretion from test runs conducted at (A) AOA = 0°, (B) AOA = 2°, (C) AOA = 4°, and (D) a repeat run at AOA = 4°. The inset in Panel (A) for the AOA = 0° test run shows the non-instrumented side ice accretion for comparison.

6.7 Block 5: Angle of Attack Sweep at T = –15 °C and U = 207 knots

An AOA sweep was conducted at T = –15 °C and U = 207 knots to evaluate that parameter’s impact on ice accretion (Block 5 of Table 6). All other test conditions, including heater settings, were fixed for this AOA sweep. Figure 33 shows the resulting ice accretions conducted at AOA = 0° (Panel (A)), AOA = 2° (Panel (B)), AOA = 4° (Panel (C)), and a repeat run at AOA = 4° (Panel (D)). The inset in Panel (A) shows the non-instrumented side for comparison against the instrumented side ice accretion. Slightly more ice accreted on the non-instrumented side for the AOA = 0°. Due to the negligible amount of ice on the instrumented side, only the non-instrumented side ice was weighed. Overall, very little ice accreted for the AOA = 0° test run. Accreted ice mass increased with increasing AOA . A higher collision efficiency at the ramp base is expected at larger AOA , which was likely a factor in the greater ice mass that was measured.

This has implications for designs that have sharper gooseneck angles in the compressor core that can promote higher collision efficiencies. Figure 33 shows that ice accretions with shark teeth features were more prominent at larger angles of attack. No shark teeth ice features were observed for tests conducted at AOA = 0° (Panel (A)), a limited amount of shark teeth features appear at AOA = 2° (Panel (B)), and more prominent shark teeth features can be seen at AOA = 4° (Panels (C) and (D)). Repeatability was good as similar ice mass, location, and appearance accreted for the two tests conducted at AOA = 4°. The strut had little impact on ice accretion throughout the test.

6.8 Block 6: Angle of Attack Sweep at T = –20 °C and U = 152.5 knots

An AOA sweep was conducted at T = –20 °C and U = 152.5 knots to evaluate that parameter’s impact on ice accretion (Block 6 of Table 6). Figure 34 shows the resulting ice accretions conducted at AOA = 0° (Panel (A)), AOA = 2° (Panel (B)), AOA = 4° (Panel (C)), and a repeat run at AOA = 4° (Panel (D)). Accreted ice mass increased with increasing AOA , where higher collision efficiency at the ramp base at a greater AOA was likely the reason for this trend. Figure 34 shows that ice accretions with shark teeth features were more prominent at larger angles of attack. No shark teeth ice features were observed for tests conducted at AOA = 0° (Panel (A)), a limited amount of shark teeth features appear at AOA = 2° (Panel (B)), and more prominent shark teeth features can be seen at AOA = 4° (Panels (C) and (D)). Repeatability was good as similar ice mass, location, and appearance accreted for the two tests conducted at AOA = 4°. The strut had little impact on ice accretion throughout the test. Compared to the AOA sweep in the previous subsection (Section 6.7), NASA/CR-2026000820 44 A B C D Flow Run# UG3611 Run# UG3610 Run# UG3609 Run# UG3636 AOA = 0 ° AOA = 2 ° AOA = 4 ° AOA = 4 ° Total = 2.6 g Total = 11.0 g Total = 20.2 g Total = 17.6 g No Sharkteeth Limited Sharkteeth Sharkteeth Sharkteeth Figure 34.—End of test run images showing the resulting ice accretion from test runs conducted at (A) AOA = 0°, (B) AOA = 2°, (C) AOA = 4°, and (D) a repeat run at AOA = 4°.

this AOA sweep was conducted at a colder total air temperature (–20 vs. –15 °C), slower airspeed (152.5 vs. 207 knots), higher IWC (3.0 vs. 2.0 g/m ) and larger MVD (41 vs. 28 μm), but with identical heater heat flux settings. Despite the differences in test conditions, the ice accretion mass, location, and appearance for all AOA test runs in this sweep were very similar to the respective test runs in the AOA sweep in the previous subsection. This may be, in part, because the surface energy balance at the ramp base was similar. The energy balance includes convection, conduction, evaporative mass transfer, and kinetic energy from impacting cloud particles. The slower airspeed (lower convective heat transfer) countered the colder total air temperature (greater convective heat transfer) between the two tests. The ice accretion process at the ramp base is complex as it requires bookkeeping energy and mass balances upstream from runback melt production, accounting for collision efficiency at all chord surfaces, and is transient in nature.

7.0 Heat Flux Icing Threshold Tests

7.1 Heat Flux Icing Threshold Objectives and General Test Matrix

A series of tests were conducted that investigated surface heat flux and the threshold values that differentiated between liquid runback (“running wet” conditions) and ice accretion. These heated surfaces when running wet act like an ice protection system. The tests provide data for heat transfer at surfaces that generate running wet conditions. Multiple objectives where set for these heat flux icing threshold tests and are listed below.

• Identify approximate minimum heat flux setting that produces full liquid melt/runback in each heater zone (with a focus on Zones 1 to 4) for an impinging icing cloud, and measure resulting surface temperatures.

• Conduct two supercooled liquid icing threshold tests at different airspeeds to compare heat fluxes and resulting icing measurements.

• Conduct two ice crystal icing threshold tests at different airspeeds to compare heat fluxes and resulting icing measurements.

• Conduct dry (no icing cloud) tests at same aerothermal conditions and heater settings conducted during the SCL and IC icing threshold tests and measure corresponding surface temperatures.

NASA/CR-2026000820 45 TABLE 9.—TEST CONDITIONS FOR THE TWO SCL AND TWO IC ICING THRESHOLD TESTS ARE SHOWN [Multiple heat flux values were set in each heating zone to find the icing and running-wet threshold.]

Test run Cloud T U , AOA , MVD , TWC , Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 0, ID no. type, °C knots ° μm g/m heat flux, heat flux, heat flux, heat flux, heat flux, heat flux, 2 2 2 2 2 2 SCL or IC W/in W/in W/in W/in W/in W/in UG3625 SCL –6 152.5 0 30 0.44 Various Various Various Various Various Various UG3639 SCL –6 207.0 0 30 0.44 Various Various Various Various Various Various UG3617 IC –15 152.5 0 27 1.9 Various Various Various Various Various Various UG3618 IC –15 207.0 0 28 2.0 Various Various Various Various Various Various Table 9 shows the four conditions that were tested for the heat flux threshold tests. The two SCL and two IC icing threshold tests were conducted at airspeeds of 152.5 and 207 knots. All other test conditions ( T , AOA , MVD , and TWC ) were held constant for the respective icing cloud tests. Due to limited characterized ice crystal icing clouds, small variations in MVD (27 vs. 28 μm) and TWC (1.9 vs. 2.0 g/m ) exist between the two IC tests. Each test run utilized multiple heat flux settings and is indicated with “Various” in Table 9 for the six heater zones. After conducting the icing threshold tests, the same test conditions and heater settings were run without the icing cloud to record the corresponding surface temperatures in dry conditions for comparison.

7.2 Testing Procedures

The icing threshold tests began with all six heating zones of the SIDRM test article heated to elevated temperatures such that when the SCL or IC cloud was activated, there was full liquid runback on the main body. The heat flux was systematically reduced in intervals starting from the back end moving forward until that zone began to accrete ice. Each new heater setting was held for approximately 3 min until thermocouples read new steady state temperatures. The test was run as a continuous spray from one heater setting to the next, so only power to the heaters, heat flux gauge (not provided in this report), thermocouple, and visual data was acquired for these tests. The final accreted ice mass and ice shape geometry were not recorded for these tests. The general testing procedures for the heat flux icing threshold tests (icing cloud activated) are outlined below.

1. Run up IRT to target test airspeed and air temperature.

2. Activate SIDRM heaters to (elevated) target heat flux values and wait until thermocouples read steady values.

3. Start recording data 30 s prior to spray activation.

4. Turn on ice cloud (spray on).

5. Verify all heater zones ice free after initial (elevated) heater setting (all liquid runback).

6. Verify all thermocouple measurements read steady state for at least 30 s.

7. Reduce heat flux in aft sections of SIDRM until ice accretes in or near heater Zone 4.

8. Verify all thermocouple measurements read steady state for at least 30 s.

9. Reduce heat flux systematically moving forward (from Zone 3 to Zone 2 to Zone 1) until ice accretes in each respective zone and verify steady state thermocouple measurements for at least 30 s.

10. Turn off icing cloud (SIDRM heaters turned off simultaneously with spray off).

11. Continue holding tunnel airspeed and air temperature constant as data systems continue recording 30 s post spray.

12. Stop data recording systems and shut down drive fan.

NASA/CR-2026000820 46 13. Enter test section and take photographs of accreted ice.

14. Remove all ice from SIDRM and clean test article, preparing for next test point.

After the icing threshold tests were completed, the corresponding dry (no icing cloud) tests were conducted. The heater settings used during the icing threshold tests are repeated for these dry tests to measure the corresponding surface temperatures. The testing procedures for these dry tests are outlined below.

1. Run up IRT to target test airspeed and air temperature.

2. Activate SIDRM heaters to initial heat flux values and wait until thermocouples read steady values.

3. Start recording data.

4. Verify all thermocouple measurements read steady state for at least 30 s.

5. Reduce heat flux following the same order as was systematically done for the icing threshold tests, verifying steady state thermocouple measurements for at least 30 s at each heater setting.

6. After conducting final heater setting and holding for 30 s at steady state temperatures, turn off heaters.

7. Stop data recording systems and shut down drive fan.

7.3 Heat Flux Threshold Tests—Supercooled Liquid Icing at 152.5 knots

Table 10 provides heat flux values used during the SCL icing heat flux threshold test conducted at 152.5 knots (Run no. UG3625), with resulting icing descriptions and steady state surface temperatures.

Data was collected for nine heater settings where heater settings listed “a” through “i” occurred chronologically. Efforts were made to systematically reduce heat flux setting from the highest (Heater Setting “a”) to lowest setting (Heater Setting “i”), however identifying the icing threshold methodically from Zone 4 to Zone 1 was imperfectly executed for this test run. Cells shaded in light green indicate the approximate heat flux threshold between icing and liquid runback in that heater zone. Table 10 shows how icing in Zone 2 unintentionally occurred first in the sequence. Despite that, it is not believed to have impacted the approximate heat flux icing threshold for the downstream zones. The corresponding steady state surface temperatures from the dry test runs (no icing cloud) are provided at the bottom half of the table. Note that not all heater settings conducted during the icing test run were conducted during the dry test runs. Icing threshold test runs with a corresponding dry test are indicated with a shaded orange cell in the first column of Table 10. As an example, there was a corresponding dry test run for Heater Setting “a”, but not for Heater Setting “b”. Of note, the thermocouple located at the centerline leading edge, T301, was not functioning properly during any of the heat flux threshold tests and is not provided in the tables in this section. Also, the thermocouple labeled T307 is located directly under the strut. Due to the absence of heating directly under the strut, T307 measured lower temperatures compared to surrounding thermocouples.

NASA/CR-2026000820 47 NASA/CR-2026000820 TABLE 10.—HEAT FLUX VALUES FOR ALL HEATER SETTINGS WITH A DESCRIPTION OF RESULTING ICE FOR THE SUPERCOOLED LIQUID ICING THRESHOLD TEST AT 152.5 KNOTS [Several surface thermocouple temperature readings are provided for “wet” (exposed to icing cloud), and corresponding “dry” (no icing cloud) test conditions.]

Heater settings Steady state surface TC temperatures (during icing test run or for corresponding “dry” test run) Heater Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zones Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 setting, heat flux, heat flux, heat flux, heat flux, heat flux, heat flux, where iced, T201, T40, T302, T303, T304, T305, T306, T207, T307, T407, T310, T311, T312, T313, T314, T315, 2 2 2 2 2 2 letter W/in W/in W/in W/in W/in W/in heater zone °C °C °C °C °C °C °C °C °C °C °C °C °C °C °C °C Cloud on tests (“wet”) a 7.1 2.1 2.8 3.7 6.4 4.5 Local strut 11.5 10.8 6.1 5.1 5.2 5.7 5.1 4.8 –0.1 4.5 5.4 6.9 8.0 21.0 25.8 28.2 b 5.5 1.7 2.3 3.2 6.4 4.5 Local strut 8.0 7.4 3.7 3.1 3.2 3.7 2.9 2.8 –1.2 2.5 3.5 4.8 6.2 21.2 26.5 28.7 c 4.2 1.3 1.8 2.6 6.4 4.5 Local strut 4.7 4.4 1.6 1.3 1.4 1.7 1.1 0.8 –2.1 0.5 1.7 3.4 5.1 22.0 27.3 28.9 d 3.5 1.2 1.8 2.6 6.4 4.5 2, 4, strut 3.1 2.8 0.5 –0.2 –0.2 0.4 0.3 0.2 –2.4 –0.1 1.5 3.2 5.1 22.7 28.1 29.1 e 3.5 1.2 1.8 2.2 6.3 4.5 2, 4, strut 3.0 2.8 0.4 –0.7 –0.9 –0.5 0.0 0.0 –2.5 –0.3 0.4 1.8 4.1 23.5 29.3 31.9 f 3.5 1.2 1.4 1.7 6.3 4.5 2, 3, 4 3.1 2.9 0.5 –0.8 –1.2 –1.2 –0.9 –1.1 –3.1 –1.5 –1.1 0.3 2.9 23.6 30.3 34.2 g 2.5 1.2 1.4 1.7 2.7 2.8 2, 3, 4 1.2 1.1 0.1 –0.9 –1.3 –1.4 –1.0 –1.4 –3.1 –1.8 –1.4 –0.3 1.1 10.6 13.9 24.0 8 h 1.6 1.2 1.4 1.7 1.9 1.9 2, 3, 4 0.4 0.3 –0.6 –0.8 –1.1 –1.5 –1.0 –1.4 –3.2 –1.8 –1.6 –0.9 –0.3 4.3 5.9 14.1 i 1.2 1.2 1.4 1.5 1.3 1.3 1, 2, 3, 4 –0.2 –0.3 –1.1 –0.9 –1.1 –1.5 –1.1 –1.5 –3.3 –1.8 –2.3 –1.6 –1.2 1.4 2.4 8.3 Cloud off tests (“dry”) a 7.1 2.1 2.8 3.7 6.3 4.4 N/A 22.0 21.3 14.5 13.1 13.3 14.1 14.2 12.8 7.3 12.7 11.0 11.7 12.6 26.4 30.7 38.9 c 4.2 1.3 1.8 2.6 6.3 4.4 N/A 11.0 10.6 6.8 6.1 6.4 7.2 7.6 6.8 3.1 6.7 6.0 6.6 7.9 24.6 29.6 38.2 d 3.5 1.2 1.8 2.6 6.3 4.4 N/A 8.6 8.3 5.1 4.6 5.0 6.0 6.8 6.3 2.6 6.1 5.8 6.3 7.6 24.4 29.4 38.1 e 3.5 1.2 1.8 2.2 6.3 4.4 N/A 8.5 8.1 4.9 4.5 4.9 5.8 6.6 6.1 2.5 6.0 4.6 4.8 6.2 24.1 29.2 38.0 f 3.5 1.2 1.4 1.7 6.3 4.4 N/A 8.5 8.1 4.9 4.3 4.5 5.0 5.0 4.2 1.2 4.1 2.7 2.9 4.4 23.4 28.8 37.8 g 2.5 1.2 1.4 1.7 2.7 2.8 N/A 5.2 4.9 3.3 3.4 3.9 4.5 4.5 3.9 0.9 3.7 2.3 2.1 2.4 8.6 10.3 21.8 i 1.2 1.2 1.4 1.5 1.3 1.3 N/A 1.3 1.2 1.3 2.4 3.2 4.0 4.2 3.5 0.6 3.4 1.6 1.2 1.1 2.1 2.5 8.1 Figure 35 graphically shows the heat flux settings and resulting surface temperatures of representative thermocouples in heating Zones 1 to 4 from Table 10. Panels (B) and (A), respectively, show the heat flux and resulting temperatures for Zones 1 to 4 when the SCL cloud was activated (“wet”). Similarly, Panels (D) and (C), respectively, show the corresponding heat fluxes and surface temperatures for the “dry” tests (no cloud). Heater settings listed “a” through “i” occurred chronologically. To avoid repeating descriptions of this figure layout again, each of the remaining subsections in this section (Section 7.0) will have the same figure layout presented. Both Figure 35 and Table 10 show that surface temperatures of heating zones where ice accretion occurred were near or below freezing values (see second row of table for thermocouple and heater zone relations). They also shows that cloud activated temperatures are lower than dry temperatures for identical heater settings. This is expected as the surface for running-wet tests experienced the additional evaporative cooling energy flux in addition to the convective cooling heat flux at the surface.

Figure 36 shows snapshots of ice accretions throughout the duration of the SCL icing heat flux threshold test conducted at 152.5 knots. Panel (A) shows the approximate location of Heating Zones 1 to 4 with transparently colored boxes, along with the representative thermocouple location in each zone for reference.

Panel (A) shows ice that had accreted in Zone 2 for heater setting “d”. As mentioned earlier, the intent was to systematically work back to front, but the icing threshold was unintentionally reached first in Zone 2 . Ice had also accreted locally around the strut in Panel (A). The absence of a thin film heater directly under the struts resulted in a colder surface around the struts if the Zone 3 heater was activated. For these tests, Zone 3 was only considered iced if there was ice that had accreted lateral to and away from the struts. Ice accreted on the unheated extensions, and on the leading edge of the struts, but are not considered for these tests as the focus was the heated main body. Panel (B) shows Heater Setting “e”, where icing was observed to occur in Zone 4. Zone 3 was still considered clear of ice for Heater Setting “e”. Panel (C) shows Heater Setting “f”, where the Zone 3 heat flux was reduced sufficiently to result in ice in that zone (now Zones 2, 3, and 4 are iced). Panel (D) shows Heater Setting “i”, where Zone 1 became iced.

25 25 Zn 1 - Wet T401 → Zn 1 - Dry T401 → Wet Dry T303 → T303 → Zn 2 - Wet Zn 2 - Dry Temperatures Temperatures 20 20 C) Zn 3 - Wet T407 → C) Zn 3 - Dry T407 → ° ° T311 → T311 → Zn 4 - Wet Zn 4 - Dry 15 15 10 10 5 5 Surface Temperature ( Surface Temperature ( 0 0 -5 -5 a b c d e f g h i a b c d e f g h i A C Setting Setting 8 8 Heat Fluxes Heat Fluxes Zn 1 Zn 1 ) ) 2 2 6 6 Zn 2 Zn 2 Zn 3 Zn 3 4 4 Zn 4 Zn 4 2 2 Heat Flux (W/m Heat Flux (W/m 0 0 a b c d e f g h i a b c d e f g h i D B Setting Setting Figure 35.—(A) Representative wet surface temperatures for Zones 1 to 4, (B) resulting from the various heat flux settings tested, (C) along with the corresponding dry surface temperatures (D) for the same heat flux settings for the SCL icing threshold test conducted at 152.5 knots.

NASA/CR-2026000820 49 D A B C Flow Heater setting: f Heater setting: i Heater setting: e Heater setting: d Zones 1 - 4 iced Zones 2, 4, strut iced Zones 2 - 4 iced Zones 2, strut iced Figure 36.—A sequence of ice accretions resulting from the supercooled liquid icing threshold test at 152.5 knots (Run no. UG3625), where the heat flux was largely systematically reduced in intervals from the back end moving forward (from Panel A to D).

7.4 Heat Flux Threshold Tests—Supercooled Liquid Icing at 207 knots

Table 11 provides heat flux values used during the SCL icing heat flux threshold test conducted at 207 knots (Run no. UG3639), with resulting icing descriptions and steady state surface temperatures. Data was collected for 16 heater settings that were systematically reduced from the highest heat flux setting (Heater Setting “a”) to lowest flux setting (Heater Setting “p”). Again, not all heater settings conducted during the icing test run have a corresponding dry test run. Those that do are indicated with a shaded orange cell in the first column. Cells shaded in light green indicate the approximate heat flux threshold between icing and liquid runback in that heater zone.

Figure 37 graphically shows the heat flux settings and resulting surface temperatures of representative thermocouples in heating Zones 1 to 4 from Table 11. As before, both Figure 37 and Table 11 show that surface temperatures of heating zones where ice accretion occurred were near or below freezing values.

Similarly, the table also shows that cloud activated temperatures are lower than dry temperatures for identical heater settings due to the additional evaporative cooling at the surface. The icing threshold heat flux values in Zones 1, 2, and 3 are greater for this higher airspeed test run compared to the 152.5 knot test run in the previous subsection (Section 7.3). This is inline when considering the energy balance at those surfaces. The greater airspeed increased convective heat transfer from the heated surface. Therefore, a greater supply of heat is required to elevate the surface temperatures high enough above freezing to keep the impinging supercooled liquid cloud as a runback liquid. In addition, the water mass flow rate of the freestream icing cloud was about 36% greater for the higher airspeed test (for the same TWC , the water mass flow rate will be the ratio of airspeeds of 207 to 152.5 knots). This too will require a greater supply of heat to keep the greater impinging water mass flux as a runback liquid on the surfaces. The icing threshold heat flux for Zone 4 was equal (2.2 W/m ) between the two airspeed test runs. It is possible that the Zone 4 threshold value for the 207 knot test run is higher than what was measured. The heat flux step decrement for Heater Setting “f’ to “g”), and it is possible that a more taken in Zone 4 was large (from 2.9 to 2.2 W/m accurate threshold value is greater than what was determined.

Figure 38 shows the sequence of ice accretions throughout the duration of the SCL icing threshold test conducted at 207 knots. The snapshots show the heater setting at which the heat flux threshold between how icing and liquid runback was crossed. The figure shows how ice accreted in Zone 4 in Panel (A), and then progressed forward at sequentially lower heat flux settings in Zones 3, 2, and then 1 in Panels (B), (C), and (D), respectively.

NASA/CR-2026000820 50 NASA/CR-2026000820 TABLE 11.—HEAT FLUX VALUES FOR ALL HEATER SETTINGS WITH A DESCRIPTION OF RESULTING ICE FOR THE SUPERCOOLED LIQUID ICING THRESHOLD TEST AT 207 KNOTS [Several surface thermocouple temperature readings are provided for “wet” (exposed to icing cloud), and corresponding “dry” (no icing cloud) test conditions.]

Heater settings Steady state surface TC temperatures (during icing test run or for corresponding “dry” test run) Heater Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zones Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 setting, heat flux, heat flux, heat flux, heat flux, heat flux, heat flux, where iced, T201, T40, T302, T303, T304, T305, T306, T207, T307, T407, T310, T311, T312, T313, T314, T315, 2 2 2 2 2 2 letter W/in W/in W/in W/in W/in W/in heater zone °C °C °C °C °C °C °C °C °C °C °C °C °C °C °C °C Cloud on tests (“wet”) a 15.4 3.6 3.9 5.3 6.4 4.5 All clear 23.4 21.9 13.0 11.0 11.1 10.5 7.7 6.8 1.0 6.0 6.7 8.1 9.0 17.3 20.3 22.2 b 13.0 3.4 4.2 5.0 5.7 3.9 All clear 19.2 18.0 10.2 8.5 8.7 8.5 6.7 6.5 1.1 5.7 6.4 7.3 7.9 15.0 17.7 18.9 c 10.8 3.1 4.2 4.6 5.0 3.3 All clear 15.8 14.7 8.2 6.9 7.1 6.8 6.0 6.1 1.1 5.5 5.9 6.6 7.1 13.1 15.3 16.1 d 8.9 2.6 4.2 4.0 4.4 2.8 All clear 12.2 11.3 5.7 4.7 4.8 4.6 5.2 5.7 0.9 5.1 4.5 4.7 5.0 10.5 12.4 12.5 e 7.1 2.1 4.2 3.4 3.8 2.4 All clear 8.8 8.0 3.5 2.7 2.9 2.7 4.6 5.4 0.8 4.6 3.7 3.3 3.5 8.3 9.9 9.5 f 5.5 2.1 4.2 2.9 3.3 1.9 All clear 6.1 5.5 2.4 2.2 2.5 2.2 4.5 5.2 0.8 4.5 2.4 1.6 1.7 6.0 7.4 6.2 g 4.8 1.9 4.2 2.2 2.8 1.5 4 4.6 4.0 1.4 1.3 1.6 1.3 4.2 4.9 0.7 4.3 1.1 –0.8 –1.3 2.8 4.6 4.0 h 4.8 1.9 3.6 2.2 2.5 1.3 4 4.5 4.1 1.4 1.3 1.4 0.6 2.9 3.6 0.0 3.0 0.4 –1.7 –1.8 1.3 2.9 2.3 i 4.8 1.9 3.1 2.2 2.3 1.2 4 4.6 4.1 1.4 1.3 1.2 0.1 2.4 2.4 –0.4 2.1 –0.7 –1.9 –2.4 0.9 2.3 1.5 j 4.8 1.9 2.5 2.2 2.3 1.2 4 4.6 4.1 1.4 1.3 1.2 0.0 1.7 1.6 –0.9 1.2 –1.0 –1.7 –2.1 0.6 2.1 1.2 k 4.8 1.9 2.1 2.2 2.3 1.2 3, 4 4.6 4.2 1.5 1.4 1.3 0.0 0.9 0.8 –1.5 0.6 –1.2 –1.8 –2.3 0.4 2.0 1.2 l 4.8 1.9 1.6 2.2 2.3 1.2 3, 4 4.6 4.1 1.5 1.4 1.2 –0.1 0.1 –0.1 –2.3 –0.5 –2.1 –2.2 –2.0 1.6 3.2 0.8 m 4.2 1.5 1.6 2.2 2.3 1.2 2, 3, 4 3.3 2.8 0.1 –0.6 –0.4 –0.6 –0.1 –0.6 –2.5 –1.3 –1.9 –1.6 –1.3 2.2 3.9 0.9 n 3.0 1.5 1.6 2.2 2.3 1.2 2, 3, 4 1.2 0.9 –0.9 –1.3 –1.2 –0.9 –0.1 –0.8 –2.5 –1.5 –1.8 –1.4 –1.1 2.4 3.9 1.2 o 2.0 1.5 1.6 2.2 2.3 1.2 1, 2, 3, 4 0.2 0.1 –1.6 –1.6 –1.3 –1.0 –0.1 –0.9 –2.6 –1.5 –1.8 –1.4 –1.1 2.5 4.1 1.1 p 1.6 1.5 1.6 2.2 2.3 1.2 1, 2, 3, 4 –0.4 –0.2 –1.7 –1.5 –1.3 –1.0 –0.1 –1.0 –2.6 –1.4 –1.7 –1.3 –1.1 2.6 4.2 1.5 Cloud off tests (“dry”) a 15.3 3.6 3.9 5.3 6.4 4.5 N/A 41.8 41.1 25.1 20.9 20.1 19.9 18.4 15.6 8.1 15.5 12.9 13.7 13.9 21.4 24.0 30.2 b 13.0 3.3 4.2 4.9 5.7 3.9 N/A 35.8 35.0 21.8 18.7 18.6 19.3 19.1 16.8 9.2 16.6 12.8 12.9 13.0 19.1 21.2 26.5 d 8.9 2.6 4.2 4.0 4.4 2.8 N/A 23.6 22.9 14.4 12.8 13.4 15.3 17.1 15.9 8.7 15.6 10.5 9.7 9.5 14.0 15.4 18.3 f 5.5 2.1 4.2 2.9 3.3 1.9 N/A 13.7 13.2 8.7 8.5 9.8 12.4 15.5 14.9 8.0 14.6 7.7 5.9 5.6 9.0 10.0 11.0 h 4.8 1.9 3.6 2.2 2.5 1.3 N/A 11.3 10.8 6.9 6.9 8.0 10.2 12.8 12.2 6.2 11.8 5.1 3.1 2.8 5.6 6.3 6.4 k 4.8 1.9 2.0 2.2 2.3 1.2 N/A 11.3 10.8 6.9 6.6 7.0 7.5 7.4 6.0 2.1 5.6 2.7 1.8 1.7 4.1 4.9 4.6 l 4.8 1.9 1.6 2.2 2.3 1.2 N/A 11.2 10.8 6.8 6.5 6.8 6.8 5.9 4.3 1.0 3.9 2.1 1.4 1.4 3.9 4.7 4.4 m 4.2 1.5 1.6 2.2 2.3 1.2 N/A 8.7 8.3 4.7 4.3 4.6 4.9 4.8 3.6 0.5 3.3 1.8 1.2 1.2 3.7 4.6 4.2 n 3.0 1.5 1.6 2.2 2.3 1.2 N/A 5.5 5.2 3.3 3.6 4.1 4.6 4.6 3.4 0.4 3.1 1.7 1.1 1.1 3.6 4.5 4.1 o 2.0 1.5 1.6 2.2 2.3 1.2 N/A 2.9 2.7 2.1 3.0 3.7 4.3 4.4 3.3 0.3 2.9 1.6 1.0 1.0 3.5 4.4 4.1 p 1.6 1.5 1.6 2.2 2.3 1.2 N/A 1.7 1.5 1.5 2.6 3.5 4.1 4.2 3.2 0.3 2.8 1.5 0.9 1.0 3.5 4.4 4.0 45 45 Zn 1 - Wet T401 → Zn 1 - Dry T401 → Wet 40 40 Zn 2 - Wet T303 → Zn 2 - Dry T303 → Temperatures Dry 35 35 C) Zn 3 - Wet C) Zn 3 - Dry T407 → T407 → ° ° Temperatures Zn 4 - Dry Zn 4 - Wet 30 T311 → 30 T311 → 25 25 20 20 10 10 5 5 Surface Temperature ( Surface Temperature ( 0 0 -5 -5 a b c d e f g h i j k l m n o p a b c d e f g h i j k l m n o p A C Setting Setting 20 20 Zn 1 Zn 1 ) Heat Fluxes ) Heat Fluxes 2 2 15 15 Zn 2 Zn 2 Zn 3 Zn 3 10 10 Zn 4 Zn 4 5 5 Heat Flux (W/m Heat Flux (W/m 0 0 a b c d e f g h i j k l m n o p a b c d e f g h i j k l m n o p D B Setting Setting Figure 37.—(A) Representative wet surface temperatures for Zones 1 to 4, (B) resulting from the various heat flux settings tested, (C) along with the corresponding dry surface temperatures (D) for the same heat flux settings for the SCL icing threshold test conducted at 207 knots.

B C D A Flow Heater setting: o Heater setting: m Heater setting: k Heater setting: g Zones 1 - 4 iced Zone 4 iced Zones 2 - 4 iced Zones 3 - 4 iced Figure 38.—A sequence of ice accretions resulting from the supercooled liquid icing threshold test at 207 knots (Run no. UG3639), where the heat flux was systematically reduced in intervals from the back end moving forward (from Panel (A) to (D)).

7.5 Heat Flux Threshold Tests—Ice Crystal Icing at 152.5 knots

Table 12 provides heat flux values used during the ice crystal icing heat flux threshold test conducted at 152.5 knots (Run no. UG3617), with resulting icing descriptions and steady state surface temperatures.

Data was collected for 14 heater settings that were systematically reduced from the highest heat flux setting (Heater Setting “a”) to lowest flux setting (Heater Setting “n”). A corresponding dry test run was conducted for all heater settings performed during the icing test runs. Cells shaded in light green indicate the approximate heat flux threshold between icing and liquid runback in that heater zone. Ice accretion was observed to occur only in Zones 2 and 3 and the threshold is reflected in the table with just two light green shaded cells.

NASA/CR-2026000820 52 NASA/CR-2026000820 TABLE 12.—HEAT FLUX VALUES FOR ALL HEATER SETTINGS WITH A DESCRIPTION OF RESULTING ICE FOR THE ICE CRYSTAL ICING THRESHOLD TEST AT 152.5 KNOTS [Several surface thermocouple temperature readings are provided for “wet” (exposed to icing cloud), and corresponding “dry” (no icing cloud) test conditions.]

Heater settings Steady state surface TC temperatures (during icing test run or for corresponding “dry” test run) Heater Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zones Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zn 6 setting, heat flux, heat flux, heat flux, heat flux, heat flux, heat flux, where iced, T201, T40, T302, T303, T304, T305, T306, T207, T307, T407, T310, T311, T312, T313, T314, T315, 2 2 2 2 2 2 letter W/in W/in W/in W/in W/in W/in heater zone °C °C °C °C °C °C °C °C °C °C °C °C °C °C °C °C Cloud on tests (“wet”) a 9.8 4.2 5.6 5.6 6.0 3.9 Local strut 10.7 9.3 11.2 13.3 15.2 15.8 11.0 6.3 –0.9 6.4 9.5 10.7 11.3 17.8 20.3 23.0 b 8.9 3.9 6.3 5.6 6.0 3.9 Local strut 7.8 6.8 8.7 10.9 13.1 14.7 11.7 7.0 –0.3 9.3 9.9 10.6 11.0 17.5 20.0 22.4 c 8.9 3.4 7.1 5.0 6.0 3.9 Local strut 6.4 5.7 6.3 8.0 10.2 13.0 12.1 8.0 0.6 10.4 8.9 8.6 9.1 17.1 19.6 21.4 d 8.0 2.8 7.5 4.6 5.0 3.3 Local strut 2.8 2.4 3.4 4.8 7.1 10.9 11.6 9.3 0.9 10.1 8.3 7.4 7.5 13.1 14.9 17.0 e 7.1 2.4 6.7 4.0 4.4 2.8 Local strut 2.9 2.2 1.5 2.3 4.2 7.7 8.9 5.8 –0.3 8.1 5.9 4.8 4.9 10.0 11.5 12.5 f 6.3 2.4 6.3 3.7 3.8 2.3 Local strut 2.4 1.9 1.2 2.0 3.9 7.1 7.9 4.7 –0.9 6.8 4.6 3.4 3.4 7.4 8.5 9.0 g 6.3 2.4 5.6 3.7 3.3 1.9 Local strut 2.5 1.9 1.2 1.9 3.5 5.7 4.4 2.5 –2.3 3.0 3.5 2.7 2.7 4.9 5.6 5.4 h 6.3 2.4 4.9 3.4 2.8 1.5 Lateral of strut 2.4 1.9 1.1 1.8 3.1 4.7 3.0 1.1 –3.5 1.2 2.2 1.5 1.5 2.8 3.3 2.6 i 6.3 2.4 4.2 3.4 2.8 1.5 Lateral of strut 2.4 1.8 1.1 1.6 2.7 3.7 1.6 –0.2 –4.5 –0.1 1.5 1.0 0.9 2.3 2.8 1.8 j 6.3 2.4 3.6 3.4 2.8 1.5 Lateral of strut 2.2 1.9 1.0 1.5 2.3 2.5 0.2 –1.4 –5.6 –1.4 0.7 0.5 0.4 1.9 2.5 1.5 k 6.3 2.4 3.1 3.4 2.8 1.5 3 2.3 1.8 1.0 1.4 1.9 1.7 –1.0 –2.6 –6.5 –2.5 0.1 0.0 0.1 1.5 2.3 1.3 l 6.3 1.9 3.1 3.4 2.8 1.5 2, 3 2.0 1.6 –0.3 –0.1 0.3 0.2 –1.8 –2.8 –6.8 –2.7 –0.1 –0.1 –0.1 1.3 2.1 1.2 m 4.8 1.9 3.1 3.4 2.8 1.5 2, 3 1.2 0.9 –1.1 –0.5 0.1 0.1 –1.8 –2.6 –6.8 –2.6 –0.1 –0.1 –0.1 1.3 2.1 1.2 n 3.5 1.9 3.1 3.4 2.8 1.5 2, 3 –0.9 –0.8 –2.0 –1.1 –0.2 0.1 –1.7 –2.5 –6.8 –2.4 –0.1 –0.1 –0.1 1.3 2.1 1.1 Cloud off tests (“dry”) a 9.8 4.2 5.5 5.6 6.0 3.9 N/A 27.1 26.2 19.0 18.9 20.5 22.7 23.2 20.4 10.0 20.5 13.0 13.1 12.9 19.9 22.5 26.1 b 8.9 3.9 6.3 5.6 6.0 3.9 N/A 23.5 22.7 16.5 16.8 18.9 22.5 25.2 23.3 11.9 23.4 14.2 13.7 13.2 20.1 22.6 26.2 c 8.9 3.3 7.0 4.9 6.0 3.9 N/A 21.8 21.0 14.1 13.8 16.1 21.2 26.6 26.1 13.7 26.3 13.6 11.9 11.4 19.8 22.5 26.1 d 8.0 2.8 7.4 4.6 5.0 3.3 N/A 17.7 17.0 10.4 10.2 12.9 19.2 26.6 27.3 14.6 27.5 13.3 10.9 9.9 15.5 17.2 21.0 e 7.1 2.3 6.6 4.0 4.4 2.8 N/A 13.7 13.1 7.0 6.5 8.9 14.8 22.1 23.0 11.8 23.1 10.1 7.7 6.8 11.8 13.3 15.8 f 6.3 2.4 6.3 3.7 3.8 2.4 N/A 10.9 10.2 5.3 5.3 7.6 13.0 19.5 20.2 9.5 20.3 8.1 5.7 4.8 8.4 9.6 10.6 g 6.3 2.4 5.5 3.7 3.3 1.9 N/A 11.1 10.4 5.5 5.4 7.3 11.8 17.1 17.3 7.7 17.3 7.0 5.1 4.2 6.0 6.7 6.9 h 6.3 2.4 4.9 3.4 2.8 1.5 N/A 11.1 10.4 5.5 5.2 6.9 10.5 14.4 14.1 5.6 14.0 5.1 3.4 2.6 3.4 3.8 3.2 i 6.3 2.4 4.2 3.4 2.8 1.5 N/A 11.0 10.4 5.4 5.0 6.3 9.0 11.8 11.0 3.5 10.9 3.9 2.7 2.0 2.9 3.4 2.7 j 6.3 2.4 3.6 3.4 2.8 1.5 N/A 11.0 10.3 5.3 4.8 5.7 7.6 9.1 7.8 1.2 7.7 2.5 1.9 1.4 2.5 3.1 2.4 k 6.3 2.4 3.0 3.4 2.8 1.5 N/A 11.0 10.3 5.2 4.6 5.3 6.4 6.8 5.2 –0.6 5.0 1.5 1.3 1.0 2.2 2.9 2.2 l 6.3 1.9 3.1 3.4 2.8 1.5 N/A 9.8 9.1 3.3 2.1 2.6 4.1 5.4 4.4 –1.3 4.2 1.2 1.0 0.7 2.0 2.6 2.0 m 4.8 1.9 3.1 3.4 2.8 1.5 N/A 5.4 4.9 1.2 1.0 1.9 3.6 5.0 4.1 –1.5 4.0 1.0 0.9 0.6 1.9 2.6 1.9 n 3.5 1.9 3.1 3.4 2.8 1.5 N/A 1.5 1.1 –0.7 0.0 1.2 3.2 4.7 3.9 –1.6 3.8 0.9 0.8 0.5 1.8 2.5 1.9 Figure 39 graphically shows the heat flux settings and resulting surface temperatures of representative thermocouples in heating Zones 1 to 4 from Table 12. Both Figure 39 and Table 12 show that surface temperatures for Zones 2 and 3 were near or below freezing values when ice accretion occurred. The table also shows that cloud activated temperatures are lower than dry temperatures for identical heater settings due to the additional evaporative cooling at the surface.

Figure 40 shows snapshots of ice accretions throughout the duration of the IC icing threshold test conducted at 152.5 knots. Panels (A) and (B) show how the main body is clear of ice except for locally around the strut for Heater Settings “g” and “h”. Again, Zone 3 was only considered iced if there was ice that had accreted lateral to and away from the struts. Panel (C) shows Heater Setting “k”, where icing was observed to occur in Zone 3. Ice accretion progressed forward into Zone 2 and is shown in Panel (D).

Decreasing heat flux in Zone 1 did not result in any observed icing in the middle section of the span (ice near the extensions is neglected). When sufficiently warm, Zone 1 is generally used to generate liquid melt for accretion to occur in downstream zones. When Zone 1 heat flux was sufficiently reduced, the surface temperatures were too cool to produce melt and the impinging ice crystals simply bounced off the small radius surface. Ice accretion in Zone 4 was not observed as this area is aft of the strut and represents the thickest area of the test article where air speeds accelerate resulting in greater shear at the surface. The changing geometry into a convex surface is also less conducive to ice crystal icing in Zone 4.

It should be noted the limitations in conducting these ice crystal heat flux threshold tests. These tests were performed sequentially between different heater settings, with the cloud running continuously. As had been previously reported by Bartkus (Ref. 35), due to the closed loop wind tunnel, ice crystal clouds recirculated and IWC slowly increased over extended periods of spray time. These tests were performed as efficiently as possible to minimize IWC drift. Best efforts were taken during testing to run heat flux decrements between settings to reduce overall time and achieve sufficiently fine enough steps to identify the thresholds.

30 30 T401 → T401 → Zn 1 - Wet Zn 1 - Dry T303 → Zn 2 - Wet Zn 2 - Dry T303 → 25 Wet 25 Zn 3 - Wet T407 → T407 → C) C) Zn 3 - Dry Temperatures ° ° T311 → T311 → 20 Zn 4 - Wet 20 Zn 4 - Dry 15 15 5 5 Surface Temperature ( Surface Temperature ( Dry 0 0 Temperatures -5 -5 a b c d e f g h i j k l m n a b c d e f g h i j k l m n Setting Setting A C 12 12 Zn 1 Zn 1 Heat Fluxes Heat Fluxes ) ) 10 Zn 2 10 Zn 2 2 2 Zn 3 Zn 3 8 8 Zn 4 Zn 4 6 6 4 4 Heat Flux (W/m Heat Flux (W/m 2 2 a b c d e f g h i j k l m n a b c d e f g h i j k l m n D B Setting Setting Figure 39.—(A) Representative wet surface temperatures for Zones 1 to 4, (B) resulting from the various heat flux settings tested, (C) along with the corresponding dry surface temperatures (D) for the same heat flux settings for the IC icing threshold test conducted at 152.5 knots.

NASA/CR-2026000820 54 D C B A Flow Heater setting: k Heater setting: h Heater setting: l Heater setting: g Zone 3 iced Lateral strut iced Zones 2 - 3 iced Local strut iced Figure 40.—A sequence of ice accretions resulting from the ice crystal icing threshold test at 152.5 knots (Run no.

UG3617), where the heat flux was systematically reduced in intervals from the back end moving forward (from Panel (A) to (D)).

7.6 Heat Flux Threshold Tests—Ice Crystal Icing at 207 knots

Table 13 provides heat flux values used during the IC icing heat flux threshold test conducted at 207 knots (Run no. UG3618), with resulting icing descriptions and steady state surface temperatures. Data was collected for 13 heater settings that were systematically reduced from the highest heat flux setting (Heater Setting “a”) to lowest flux setting (Heater Setting “m”). A corresponding dry test run was conducted for all heater settings performed during the icing test runs. Ice accretion occurred only in Zone 3, and the heat flux threshold is reflected in the table with just the single light green shaded cell.

Figure 41 graphically shows the heat flux settings and resulting surface temperatures of representative thermocouples in heating Zones 1 to 4 from Table 13. Both Figure 41 and Table 13 shows that surface temperatures for Zone 3 were below freezing values when ice accreted. The table also shows that cloud activated temperatures are lower than dry temperatures for identical heater settings due to the additional evaporative cooling at the surface. The same heat flux setting was conducted for the final heater setting for the 207 knot test run (Heater setting “m”) and 152.5 knot test run (Heater setting “n”). Comparing the surface temperatures between those corresponding dry test runs, temperatures were lower for the faster airspeed tests. Again, the greater airspeed increased convective heat transfer from the heated surface, reducing the surface temperatures.

Figure 42 shows snapshots of ice accretions throughout the duration of the IC icing threshold test conducted at 207 knots. Panel (A) shows negligible ice at the strut and Panel (B) shows a small amount of ice growth local to the strut. Panel (C) shows Heater Setting “j”, where icing is considered to have accreted in Zone 3. Faint streaks of ice are visible and pointed out in Panel (C). Decreasing heat flux in Zones 1 and 2 did not result in any observed icing in the middle section of the span (ice near the extensions is neglected).

Overall, very little ice accreted for this IC icing threshold test run. The elevated airspeed of 207 knots may have caused more particle bounce and reduced sticking to the surface, resulting in a small amount of ice accretion.

NASA/CR-2026000820 55 NASA/CR-2026000820 TABLE 13.—HEAT FLUX VALUES FOR ALL HEATER SETTINGS WITH A DESCRIPTION OF RESULTING ICE FOR THE ICE CRYSTAL ICING THRESHOLD TEST AT 207 KNOTS [Several surface thermocouple temperature readings are provided for “wet” (exposed to icing cloud), and corresponding “dry” (no icing cloud) test conditions.]

Heater settings Steady state surface TC temperatures (during icing test run or for corresponding “dry” test run) Heater Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zones Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 setting, heat heat heat heat heat heat where iced, T201, T40, T302, T303, T304, T305, T306, T207, T307, T407, T310, T311, T312, T313, T314, T315, letter flux, flux, flux, flux, flux, flux, heater °C °C °C °C °C °C °C °C °C °C °C °C °C °C °C °C 2 2 2 2 2 2 W/in W/in W/in W/in W/in W/in zone Cloud on tests (“wet”) a 9.9 4.5 8.3 6.0 6.1 3.9 Negligible 5.7 5.2 6.7 9.5 12.8 17.0 18.8 19.1 6.2 19.3 12.0 10.6 10.2 14.1 15.3 18.3 b 8.9 3.9 7.5 5.3 5.1 2.8 Negligible 3.4 2.8 4.1 6.4 9.2 13.4 15.8 15.5 4.3 16.5 9.0 7.5 7.2 10.0 10.8 11.3 c 8.9 3.7 6.7 4.6 4.4 2.4 Negligible 3.1 2.7 3.4 5.2 7.6 10.8 11.7 12.5 1.9 12.6 6.4 4.8 4.6 7.1 7.7 7.1 d 8.0 3.4 6.0 4.0 3.8 1.9 Negligible 2.7 2.4 2.5 3.9 5.9 8.6 9.3 9.1 0.2 9.1 3.9 2.2 2.1 4.3 4.8 3.6 e 7.1 3.1 5.2 3.4 3.3 1.5 Negligible 2.2 1.9 1.5 2.8 4.5 6.8 6.5 6.5 –1.4 7.1 1.5 –0.4 –0.4 1.7 2.0 0.3 f 7.1 2.9 4.6 3.4 3.0 1.5 Local strut 2.1 1.8 0.9 1.7 3.2 5.2 5.3 4.4 –2.4 4.8 0.6 –0.8 –0.8 0.5 0.7 –0.4 g 7.1 2.9 3.9 3.4 3.0 1.5 Local strut 2.1 1.8 0.8 1.6 2.8 3.8 2.0 1.4 –4.1 2.1 –0.3 –1.3 –1.2 0.2 0.5 –0.7 h 7.1 2.9 3.3 3.4 3.0 1.5 Local strut 2.0 1.8 0.8 1.5 2.4 2.5 0.2 –0.7 –5.5 –0.3 –1.2 –1.9 –1.7 –0.1 0.3 –0.9 i 7.1 2.9 2.8 3.4 3.0 1.5 Local strut 2.0 1.8 0.7 1.5 2.1 1.9 –0.6 –1.9 –6.4 –2.0 –2.1 –2.5 –2.2 –0.5 0.1 –1.0 j 7.1 3.1 2.3 3.4 3.0 1.5 3 2.2 1.8 1.3 2.2 2.9 2.1 –1.3 –3.3 –7.3 –3.5 –2.8 –2.9 –2.5 –0.7 –0.1 –1.1 k 5.5 3.1 2.3 3.4 3.0 1.5 3 1.5 1.3 1.1 2.5 3.2 2.4 –1.0 –3.0 –7.3 –3.3 –2.9 –2.9 –2.6 –0.8 –0.2 –1.2 l 4.2 2.6 2.3 3.4 3.0 1.5 3 0.5 0.4 –0.4 0.7 1.4 1.3 –1.0 –2.6 –7.1 –2.9 –2.8 –2.9 –2.6 –0.8 –0.2 –1.2 m 3.5 1.9 3.1 3.4 2.8 1.5 3 –1.9 –2.0 –3.3 –2.6 –1.7 –0.3 0.2 –0.5 –5.7 –0.8 –2.1 –2.6 –2.4 –1.5 –1.1 –1.4 Cloud off tests “dry” a 9.8 4.5 8.3 6.0 6.1 3.9 N/A 21.1 20.3 13.3 14.0 16.8 21.8 27.2 25.9 14.2 25.7 12.9 10.9 10.0 14.0 15.4 18.4 b 8.9 3.9 7.5 5.3 5.1 2.8 N/A 17.3 16.6 10.1 10.6 13.0 17.7 23.2 22.0 11.5 21.7 9.9 7.7 7.0 9.7 10.6 10.8 c 8.9 3.6 6.7 4.6 4.4 2.4 N/A 16.8 16.0 9.1 9.2 11.2 15.2 19.9 18.7 9.2 18.3 7.3 5.1 4.4 7.0 7.7 7.0 d 8.0 3.4 5.9 4.0 3.8 1.9 N/A 13.7 12.9 6.9 7.1 8.9 12.4 16.5 15.1 6.6 14.7 4.5 2.2 1.6 3.9 4.5 3.1 e 7.1 3.1 5.2 3.4 3.3 1.5 N/A 10.6 9.8 4.7 4.9 6.4 9.2 12.6 11.3 3.6 10.7 1.7 –0.6 –1.1 0.8 1.4 –0.6 f 7.1 2.8 4.6 3.4 3.0 1.5 N/A 10.1 9.4 3.9 3.7 4.9 7.3 10.0 8.6 1.9 8.1 0.7 –1.1 –1.5 –0.3 0.2 –1.0 g 7.1 2.8 3.9 3.4 3.0 1.5 N/A 10.2 9.4 3.9 3.6 4.6 6.2 7.9 6.1 0.2 5.6 –0.1 –1.6 –1.9 –0.5 0.0 –1.1 h 7.1 2.8 3.3 3.4 3.0 1.5 N/A 10.2 9.4 3.9 3.5 4.2 5.2 5.8 3.7 –1.5 3.2 –1.0 –2.1 –2.3 –0.8 –0.2 –1.2 i 7.1 2.8 2.8 3.4 3.0 1.5 N/A 10.1 9.4 3.8 3.4 3.9 4.2 3.8 1.5 –3.1 0.9 –1.9 –2.6 –2.7 –1.1 –0.4 –1.3 j 7.1 3.1 2.3 3.4 3.0 1.5 N/A 10.6 9.8 4.6 4.4 4.8 4.3 2.4 –0.3 –4.4 –0.9 –2.6 –2.9 –2.9 –1.2 –0.5 –1.4 k 5.5 3.1 2.3 3.5 3.0 1.5 N/A 6.7 6.1 3.0 3.7 4.4 4.1 2.2 –0.6 –4.6 –1.1 –2.7 –3.1 –3.0 –1.3 –0.6 –1.5 l 4.1 2.6 2.3 3.5 3.0 1.5 N/A 1.9 1.5 –0.5 0.5 1.4 1.7 0.9 –1.3 –5.1 –1.8 –3.0 –3.3 –3.3 –1.5 –0.8 –1.6 m 3.5 1.9 3.1 3.4 2.8 1.5 N/A –1.2 –1.6 –3.6 –3.0 –1.9 –0.2 1.8 0.9 –3.7 0.4 –2.2 –2.9 –3.1 –2.3 –1.8 –1.8 30 30 Zn 1 - Wet T401 → Zn 1 - Dry T401 → Wet Dry T303 → T303 → 25 Zn 2 - Wet 25 Zn 2 - Dry Temperatures Temperatures T407 → T407 → Zn 3 - Wet Zn 3 - Dry C) C) ° ° T311 → T311 → 20 Zn 4 - Wet 20 Zn 4 - Dry 15 15 10 10 5 5 Surface Temperature ( Surface Temperature ( 0 0 -5 -5 a b c d e f g h i j k l m a b c d e f g h i j k l m Setting Setting A C 12 12 Zn 1 Zn 1 Heat Fluxes Heat Fluxes ) ) 10 10 2 2 Zn 2 Zn 2 8 8 Zn 3 Zn 3 Zn 4 Zn 4 6 6 4 4 Heat Flux (W/m Heat Flux (W/m 2 2 0 0 a b c d e f g h i j k l m a b c d e f g h i j k l m D B Setting Setting Figure 41.—(A) Representative wet surface temperatures for Zones 1 to 4, (B) resulting from the various heat flux settings tested, (C) along with the corresponding dry surface temperatures (D) for the same heat flux settings for the IC icing threshold test conducted at 207 knots.

C B A Faint Ice streaks in Zone 3

Flow

Heater setting: g Heater setting: j Heater setting: d Local strut iced Zone 3 iced Negligible ice Figure 42.—A sequence of ice accretions resulting from the ice crystal icing threshold test at 207 knots (Run no.

UG3618), where the heat flux was systematically reduced in intervals from the back end moving forward (from Panel (A) to (C)).

8.0 Conclusion

This report discusses data collected from icing tests conducted in 2023 using the SIDRM test article at the NASA Icing Research Tunnel. The 2023 tests utilized modified 7-in. NACA 0018 struts, which were larger compared to the 4-in. NACA 0012 struts used in the counterpart 2022 tests, for the purpose of impacting ice crystal ice accretions. Due to facility reference pressure issues in 2023 that primarily impacted the airspeed, comparison of data between the 2022 and 2023 test entries were limited. The report provides data and discussion on aerodynamic tests, supercooled liquid icing tests, ice crystal icing tests, and heat flux icing threshold tests.

Aerodynamic tests were conducted at various AOA and airspeeds to characterize the flow field around the test article. Flow separation occurred further aft on the pressure side for greater AOA , and further aft on both sides of the test article at greater airspeeds. Pressure coefficient data indicated that there was no impact on the flow due to the 0.5 in. gap between the test article and the test section for the forward 30% of the chord, where NASA/CR-2026000820 57 icing primarily occurred, but impacted flow towards the ceiling beyond 30% chord. There was good repeatability of pressure coefficient data for the forward portion of the test article between the 2022 and 2023 test entries, but the discrepancies in airspeed (due to the reference pressure issue), are likely the reason for poor pressure data repeatability for the aft portion of the test article. Finer AOA increment tests pinpointed the stagnation line at the leading edge at AOA = 0.1° for U = 100.5 knots, and at AOA = 0.3° for airspeeds of 152.5 and 207 knots.

Various parametric sweeps were conducted under supercooled liquid clouds, with the primary objective to measure that parameter’s impact on ice accretion size, location, and characteristics. Ice mass, 3D laser scans, photography, and video were primary measurements to characterize the accreted ice. Higher MVD , lower total air temperatures, lower angles of attack, and longer spray times were the primary parameters that resulted in greater ice mass. Larger droplets are more ballistic and resulted in greater collection efficiency. Colder air temperatures resulted in less shedding compared to warmer air temperature accretions (and hence less mass loss). Smaller angles of attack resulted in fewer shadow regions leading to more ice accretion. Longer spray duration times provide greater time to accrete more ice. Test article AoA and cloud MVD impacted the location of ice accretion. Test article AoA directly influenced collection efficiency along the chord of the test article creating shadow regions. Cloud MVD impacted collection efficiency along the test article chord resulting in different impingement limits downstream of the leading edge as larger droplets are more ballistic and smaller droplets follow the flow. Total air temperature and cloud MVD were the primary parameters impacting icing characteristics. Warmer air temperatures resulted in glaze ice while colder conditions resulted in rime ice accretions. Smaller MVD clouds and warmer air temperatures resulted in greater amounts of feather shedding on the steep inclined area of the test article. The larger struts accreted more ice compared to the smaller struts used during the 2022 test entry. Various cross sections of ice accretions on the main body and struts were provided for comparison for all parameter sweeps.

Parametric sweeps were conducted under ice crystal clouds. Measurements to characterize the icing included surface heat flux at six heating zones, thermocouple data, ice mass, 3D laser scans of the accreted ice (not shown in this report), and photo images. A sufficiently high surface heat flux at the leading edge (i.e., sufficiently warm) can provide a continuous supply of liquid melt downstream resulting in greater ice mass compared to a lower surface heat flux. A lower flux setting results in the leading edge cooling down enough that it ceases to produce melt for accretion downstream. Longer spray duration times, along with greater AOA test conditions resulted in greater amounts of accreted ice mass. The greater ice mass result can be directly linked to increased collision efficiency (and collection efficiency) for the greater AOA test runs. Tests conducted at greater angles of attack resulted in more orderly shark teeth ice shape features, which had been observed during full-scale engine icing tests previously conducted at NASA GRC. The location and physical appearance of ice accretions were similar between the 2022 and 2023 test entries for repeated test conditions. However, ice mass was generally lower in the 2023 tests, possibly due to the larger strut displacing ice that had accreted in that location in the 2022 tests, along with discrepancies in airspeed due to the reference pressure issue. Overall, the larger struts used during this 2023 entry had little impact on ice crystal ice accretion.

Icing threshold tests were conducted under SCL and IC clouds to determine heat flux settings that differentiate between running wet and icing conditions. These tests provided heat transfer data for surfaces that generated running wet conditions, much like an ice protection system. Heat flux threshold values were determined for the forward portion of the test article at 152.5 and 207 knots. The icing threshold heat flux was greater for the higher airspeed test runs, as additional heat was needed to overcome the energy loss at the surface due to convective cooling. Corresponding dry tests (no icing cloud) conducted at the same heater settings during the SCL and IC icing threshold tests measured warmer surface temperatures as the surface for running-wet tests experienced evaporative cooling. Current IC cloud generation capabilities at the IRT NASA/CR-2026000820 58 limited the time to conduct the heat flux threshold tests. Improving upon the systematic heat flux setting procedures can provide more accurate threshold values for both SCL and IC tests.

NASA/CR-2026000820 59

Next: Appendix A.—Supplemental Information on →

Appendix A.—Supplemental Information on

the SIDRM Test Article and Test Data

TABLE A.1.—NOMINAL LOCATION OF TYPE-K THERMOCOUPLES FLUSH WITH THE TEST ARTICLE OUTER MOLD LINE, WHERE (0, 0, 0) IS LOCATED AT THE MIDSPAN LEADING EDGE TC name, x y z Heater ID (negative towards (negative towards (negative downstream zone, floor), instrumented side), of LE), no.

in. in. in.

T201 –2.500 0.000 0.000 1 a T301 0.000 0.000 0.000 1 T401 2.500 0.000 0.000 1 T302 0.000 –0.842 –2.500 2 T303 0.000 –1.283 –5.000 2 T304 0.000 –1.723 –7.500 2 T305 0.000 –2.164 –10.000 2 T306 0.000 –2.762 –12.500 3 T207 –2.500 –4.196 –15.000 3 T307 0.000 –4.196 –15.000 3 T407 2.500 –4.196 –15.000 3 T310 0.000 –9.207 –21.480 4 T311 0.000 –10.546 –23.980 4 T312 0.000 –10.841 –26.480 4 T313 0.000 –10.830 –31.480 5 T314 0.000 –10.715 –36.480 5 T315 0.000 –7.716 –50.940 6 BT303 0.000 1.283 –5.000 2 BT307 0.000 4.196 –15.000 3 BT311 0.000 10.546 –23.980 4 BT314 0.000 10.715 –36.480 5 BT315 0.000 7.716 –50.940 6 a T301 was not functioning properly during icing tests.

TABLE A.2.—NOMINAL LOCATION OF TYPE-K THERMOCOUPLES LOCATED INTERNALLY NEAR THE SIDRM LEADING EDGE, WHERE (0, 0, 0) IS LOCATED AT THE MIDSPAN LEADING EDGE TC name, x y z Heater ID (negative towards (negative towards (negative downstream zone, floor), instrumented side), of LE), no.

in. in. in.

IT101 –3.750 0.000 –0.093 1 IT201 –1.250 0.000 –0.093 1 IT301 1.250 0.000 –0.093 1 IT401 3.750 0.000 –0.093 1 NASA/CR-2026000820 61 TABLE A.3.—NOMINAL LOCATION OF HEAT FLUX GAUGES (HFG) EPOXIED INTO POCKETS OF THE TEST ARTICLE INNER MOLD LINE, WHERE (0, 0, 0) IS LOCATED AT THE MIDSPAN LEADING EDGE.

HFG name, x y z Heater ID (negative towards (negative towards (negative downstream zone, floor), instrumented side), of LE), no.

in. in. in.

HFG302 –0.950 –0.622 –2.500 2 HFG303 –0.950 –1.063 –5.000 2 HFG304 –0.950 –1.503 –7.500 2 HFG305 –0.950 –1.944 –10.000 2 HFG306 –0.950 –2.543 –12.500 3 HFG207 –3.450 –3.977 –15.000 3 HFG307 –0.950 –3.977 –15.000 3 HFG407 0.550 –3.977 –15.000 3 HFG310 –0.950 –8.987 –21.478 4 HFG311 –0.950 –10.326 –23.977 4 HFG312 –0.950 –10.621 –26.480 4 TABLE A.4.—NOMINAL LOCATION OF TYPE-T THERMOCOUPLES INTEGRATED INTO THE HEAT FLUX GAUGES EPOXIED INTO POCKETS OF THE TEST ARTICLE INNER MOLD LINE, WHERE (0, 0, 0) IS LOCATED AT THE MIDSPAN LEADING EDGE TC name, x y z Heater ID (negative towards (negative towards (negative downstream zone, floor), instrumented side), of LE), no.

in. in. in.

TC_HFG302 –0.425 –0.622 –2.500 2 TC_HFG303 –0.425 –1.063 –5.000 2 TC_HFG304 –0.425 –1.503 –7.500 2 TC_HFG305 –0.425 –1.944 –10.000 2 TC_HFG306 –0.425 –2.543 –12.500 3 TC_HFG207 –2.925 –3.977 –15.000 3 TC_HFG307 –0.425 –3.977 –15.000 3 TC_HFG407 1.075 –3.977 –15.000 3 TC_HFG310 –0.425 –8.989 –21.478 4 TC_HFG311 –0.425 –10.326 –23.977 4 TC_HFG312 –0.425 –10.621 –26.480 4 NASA/CR-2026000820 62 TABLE A.5.—NOMINAL LOCATION OF PRESSURE TAPS LOCATED ON THE TEST ARTICLE OUTER MOLD LINE, WHERE (0, 0, 0) IS LOCATED AT THE MIDSPAN LEADING EDGE Pressure x y z Pressure x y z tap name, (negative towards (negative towards (negative (negative towards (negative towards (negative tap name, ID floor), instrumented downstream floor), instrumented downstream ID in. side), of LE), in. side), of LE), in. in. in. in.

Lower row pressure taps Upper row pressure taps P101 –16.750 0.000 0.000 P201 16.750 0.000 0.000 P102 –17.000 –0.165 –0.030 P202 17.000 –0.165 –0.030 P103 –17.250 –0.289 –0.100 P203 17.250 –0.289 –0.100 P104 –17.500 –0.377 –0.190 P204 17.500 –0.377 –0.190 P105 –17.750 –0.437 –0.300 P205 17.750 –0.437 –0.300 P106 –17.250 –0.953 –3.130 P206 17.250 –0.953 –3.130 P107 –17.250 –1.505 –6.260 P207 17.250 –1.505 –6.260 P108 –17.250 –2.770 –12.520 P208 17.250 –2.770 –12.520 P109 –17.250 –7.127 –18.780 P209 17.250 –7.127 –18.780 P110 –17.250 –9.506 –21.910 P210 17.250 –9.506 –21.910 P111 –17.250 –10.777 –25.040 P211 17.250 –10.777 –25.040 P112 –17.250 –10.840 –28.170 P212 17.250 –10.840 –28.170 P113 –17.250 –10.831 –31.300 P213 17.250 –10.831 –31.300 P114 –17.250 –10.658 –37.550 P214 17.250 –10.658 –37.550 P115 –17.250 –9.907 –43.810 P215 17.250 –9.907 –43.810 P116 –17.250 –8.080 –50.070 P216 17.250 –8.080 –50.070 P117 –17.250 –4.794 –56.330 P217 17.250 –4.794 –56.330 P118 –17.250 0.000 –62.590 P218 17.250 0.000 –62.590 P119 –17.250 0.289 –0.100 P219 17.250 0.289 –0.100 P120 –17.750 0.437 –0.300 P220 17.750 0.437 –0.300 P121 –17.250 0.953 –3.130 P221 17.250 0.953 –3.130 P122 –17.250 1.505 –6.260 P222 17.250 1.505 –6.260 P123 –17.250 2.770 –12.520 P223 17.250 2.770 –12.520 P124 –17.250 7.127 –18.780 P224 17.250 7.127 –18.780 P125 –17.250 9.506 –21.910 P225 17.250 9.506 –21.910 P126 –17.250 10.777 –25.040 P226 17.250 10.777 –25.040 P127 –17.250 10.840 –28.170 P227 17.250 10.840 –28.170 P128 –17.250 10.831 –31.300 P228 17.250 10.831 –31.300 P129 –17.250 10.658 –37.550 P229 17.250 10.658 –37.550 P130 –17.250 9.907 –43.810 P230 17.250 9.907 –43.810 P131 –17.250 8.080 –50.070 P231 17.250 8.080 –50.070 P132 –17.250 4.794 –56.330 P232 17.250 4.794 –56.330 NASA/CR-2026000820 63 TABLE A.6.—PROFILE GEOMETRY OF SIDRM MAIN BODY LISTED AS 181 POINTS [Negative “z” values refer to a chord location downstream of the main body leading edge. The profile is symmetric around the “y” coordinate. The leading edge of the 7-in. chord NACA 0018 struts occurs at z = –12.978 in., where the span extends 9.852 in.

from the strut junction leading edge. Rounded endcaps that are 0.4 in. at maximum thickness cap the open end of the struts.]

Point z, y, Point z, y, Point z, y, Point z, y, no. in. in. no. in. in. no. in. in. no. in. in.

1 0.0000 0.0000 46 –0.4783 0.4849 91 –14.5344 3.8655 136 –30.0679 10.8371 2 –0.0022 0.0457 47 –0.4863 0.4865 92 –14.7744 4.0329 137 –30.7906 10.8343 3 –0.0089 0.0909 48 –0.4943 0.4880 93 –15.0144 4.2060 138 –31.5133 10.8300 4 –0.0200 0.1353 49 –0.5023 0.4895 94 –15.2544 4.3839 139 –32.2360 10.8236 5 –0.0353 0.1783 50 –0.5103 0.4909 95 –15.4944 4.5657 140 –32.9587 10.8147 6 –0.0548 0.2197 51 –0.5183 0.4924 96 –15.7344 4.7503 141 –33.6814 10.8026 7 –0.0782 0.2590 52 –0.5263 0.4938 97 –15.9744 4.9369 142 –34.4041 10.7869 8 –0.1053 0.2958 53 –0.5343 0.4953 98 –15.9744 4.9369 143 –35.1268 10.7667 9 –0.1359 0.3298 54 –0.5423 0.4967 99 –16.4680 5.3224 144 –35.8495 10.7415 10 –0.1697 0.3606 55 –0.5503 0.4981 100 –17.4680 6.1034 145 –36.5722 10.7104 11 –0.2063 0.3880 56 –0.5583 0.4995 101 –18.4680 6.8844 146 –37.2949 10.6728 12 –0.2063 0.3880 57 –0.5663 0.5009 102 –19.4680 7.6654 147 –38.0176 10.6279 13 –0.2143 0.3933 58 –0.5743 0.5023 103 –20.2144 8.2483 148 –38.7403 10.5749 14 –0.2223 0.3983 59 –0.5823 0.5038 104 –20.2144 8.2483 149 –39.4630 10.5130 15 –0.2303 0.4031 60 –0.5903 0.5052 105 –20.4544 8.4355 150 –40.1858 10.4414 16 –0.2383 0.4078 61 –0.5983 0.5066 106 –20.6944 8.6214 151 –40.9085 10.3592 17 –0.2463 0.4122 62 –0.6063 0.5080 107 –20.9344 8.8049 152 –41.6312 10.2658 18 –0.2543 0.4164 63 –0.6063 0.5080 108 –21.1744 8.9852 153 –42.3539 10.1602 19 –0.2623 0.4204 64 –1.4680 0.6599 109 –21.4144 9.1610 154 –43.0766 10.0417 20 –0.2703 0.4243 65 –2.4680 0.8363 110 –21.6544 9.3314 155 –43.7993 9.9095 21 –0.2783 0.4279 66 –3.4680 1.0126 111 –21.8944 9.4956 156 –44.5220 9.7628 22 –0.2863 0.4315 67 –4.4680 1.1889 112 –22.1344 9.6525 157 –45.2447 9.6008 23 –0.2943 0.4348 68 –5.4680 1.3652 113 –22.3744 9.8015 158 –45.9674 9.4230 24 –0.3023 0.4381 69 –6.4680 1.5416 114 –22.6144 9.9417 159 –46.6901 9.2284 25 –0.3103 0.4411 70 –7.4680 1.7179 115 –22.8544 10.0726 160 –47.4128 9.0166 26 –0.3183 0.4441 71 –8.4680 1.8942 116 –23.0944 10.1934 161 –48.1355 8.7869 27 –0.3263 0.4469 72 –9.4680 2.0705 117 –23.3344 10.3039 162 –48.8582 8.5387 28 –0.3343 0.4496 73 –10.4544 2.2445 118 –23.5744 10.4036 163 –49.5809 8.2714 29 –0.3423 0.4522 74 –10.4544 2.2445 119 –23.8144 10.4923 164 –50.3036 7.9847 30 –0.3503 0.4547 75 –10.6944 2.2871 120 –24.0544 10.5700 165 –51.0263 7.6780 31 –0.3583 0.4571 76 –10.9344 2.3316 121 –24.2944 10.6367 166 –51.7490 7.3511 32 –0.3663 0.4594 77 –11.1744 2.3797 122 –24.5344 10.6927 167 –52.4717 7.0036 33 –0.3743 0.4616 78 –11.4144 2.4327 123 –24.7744 10.7383 168 –53.1944 6.6352 34 –0.3823 0.4638 79 –11.6544 2.4918 124 –25.0144 10.7741 169 –53.9171 6.2460 35 –0.3903 0.4658 80 –11.8944 2.5582 125 –25.2544 10.8010 170 –54.6398 5.8356 36 –0.3983 0.4678 81 –12.1344 2.6324 126 –25.4944 10.8197 171 –55.3625 5.4042 37 –0.4063 0.4698 82 –12.3744 2.7153 127 –25.7344 10.8315 172 –56.0852 4.9519 38 –0.4143 0.4716 83 –12.6144 2.8071 128 –25.9744 10.8378 173 –56.8079 4.4788 39 –0.4223 0.4734 84 –12.8544 2.9081 129 –26.2144 10.8402 174 –57.5306 3.9852 40 –0.4303 0.4752 85 –13.0944 3.0185 130 –26.4544 10.8406 175 –58.2533 3.4714 41 –0.4383 0.4769 86 –13.3344 3.1382 131 –26.4544 10.8406 176 –58.9760 2.9380 42 –0.4463 0.4786 87 –13.5744 3.2671 132 –27.1771 10.8404 177 –59.6987 2.3854 43 –0.4543 0.4802 88 –13.8144 3.4047 133 –27.8998 10.8402 178 –60.4214 1.8145 44 –0.4623 0.4818 89 –14.0544 3.5507 134 –28.6225 10.8397 179 –61.1441 1.2260 45 –0.4703 0.4834 90 –14.2944 3.7045 135 –29.3452 10.8388 180 –61.8669 0.6208 181 –62.5896 0.0000 NASA/CR-2026000820 64 TABLE A.7.—LANGMUIR-D 7-BIN DROP SIZE DISTRIBUTIONS OF SUPERCOOLED LIQUID CLOUDS PRESENTED IN THIS REPORT [End-point values are provided for each bin. The cumulative bin fraction is listed in the first column.]

SCL Cloud MVD → 18 μm 25 μm 30 μm 50 μm 90 μm Cumulative bin Drop diam., Drop diam., Drop diam., Drop diam., Drop diam., fraction μm μm μm μm μm 0 4 4 4 4 4 0.05 7 8 8 9 12 0.15 10 11 11 13 25 0.35 13 19 20 29 56 0.65 23 35 46 83 139 0.85 33 61 92 154 218 0.95 45 103 154 217 293 1 177 299 314 378 775 TABLE A.8.—PARTICLE SIZE DISTRIBUTIONS OF ICE CRYSTAL CLOUDS PRESENTED IN THIS REPORT [Mid-point values are provided for each bin. The individual bin fraction is listed in the first column.]

IC Cloud MVD → 26 μm 27 μm 28 μm 41 μm Bin Particle diam., Particle diam., Particle diam., Particle diam., fraction μm μm μm μm 0.1 5 6 6 7 0.1 12 13 14 18 0.1 16 17 18 24 0.1 20 20 22 31 0.1 24 25 26 37 0.1 29 29 30 44 0.1 34 34 35 52 0.1 41 41 41 63 0.1 50 50 50 77 0.1 71 71 74 118 NASA/CR-2026000820 65 NASA/CR-2026000820 TABLE A.9.—TEST RUN PRESPRAY CONDITIONS WITH CORRESPONDING STEADY STATE SURFACE TEMPERATURES PRIOR TO SPRAY ACTIVATION [Light orange shaded cells indicated the test condition or heater setting that was varied for the test objective block. Thermocouple T307 is located directly under the strut.

Due to the absence of heating directly under the strut, T307 measured lower temperatures compared to surrounding thermocouples.]

Test run prespray conditions Heater settings Prespray steady state surface TC temperatures Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Test run, T , U , AOA , Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 T201, T401, T302, T303, T304, T305, T306, T207, T307, T407, T310, T311, T312, T313, T314, T315, no. °C kn ° flux, flux, flux, flux, flux, flux, °C °C °C °C °C °C °C °C °C °C °C °C °C °C °C °C 2 2 2 2 2 2 W/in W/in W/in W/in W/in W/in Block 1: Repeat of 2022 test conditions at T = –15 °C UG3596 –15 152.5 0 7.1 2.8 3.3 3.2 6.3 4.0 13.9 13.2 7.9 7.3 8.0 8.8 8.0 6.1 0.1 6.3 0.9 0.7 1.9 14.8 18.7 23.1 UG3592 –15 152.5 2 7.1 2.8 2.7 3.2 6.3 4.0 16.6 15.6 11.4 9.3 8.9 8.3 5.5 3.7 –2.5 3.8 0.4 0.7 2.1 14.9 18.9 21.6 UG3581 –15 152.5 4 7.1 2.3 2.5 3.2 6.3 4.0 22.1 20.3 19.9 16.3 11.8 9.5 7.6 5.0 0.0 4.9 1.0 1.1 2.1 15.4 19.1 20.7 Block 2: Repeat of 2022 test conditions at T = –20 °C UG3599 –20 152.5 0 8.9 3.6 4.2 4.0 7.9 4.6 16.5 15.8 9.0 8.5 9.5 10.5 9.4 6.7 –2.1 6.7 0.1 0.1 1.4 17.4 22.2 25.1 UG3595 –20 152.5 2 8.9 3.6 3.3 4.0 7.9 4.6 19.1 17.7 12.7 10.4 10.1 9.5 6.8 3.3 –4.2 3.2 –0.8 –0.3 1.3 17.2 21.9 23.1 UG3594 –20 152.5 4 8.9 3.1 3.3 4.0 7.9 4.6 20.3 18.3 18.6 15.1 10.7 8.4 6.0 2.8 –4.7 2.9 –0.5 0.1 1.6 17.3 22.0 21.3 UG3626 –20 152.5 4 8.9 3.1 3.3 4.0 7.9 4.6 21.4 18.7 19.7 16.3 11.6 9.1 6.7 3.7 –2.1 3.9 0.0 0.7 2.0 17.6 22.5 21.7 Block 3: Heater surface heat flux evaluation UG3629 –20 152.5 4 7.1 3.1 3.3 4.4 7.5 5.3 15.5 13.5 16.1 14.2 10.6 8.7 6.5 3.4 –4.0 3.5 1.0 1.8 2.7 16.8 21.1 26.5 UG3627 –20 152.5 4 9.9 3.1 3.3 4.4 7.5 5.3 24.5 21.7 21.5 17.3 12.2 9.7 7.3 3.9 –3.1 3.9 1.1 1.8 2.8 16.8 21.1 26.1 UG3637 –20 152.5 4 12.0 3.1 3.3 4.4 7.5 5.3 30.1 27.3 24.9 19.3 13.2 10.1 7.7 4.0 –3.1 3.9 0.9 1.6 2.7 16.6 20.9 26.3 UG3630 –20 152.5 4 12.0 3.6 3.9 4.4 7.5 5.3 32.7 30.0 29.4 24.3 18.0 14.8 11.7 7.8 –1.3 7.8 2.7 2.8 3.6 17.5 21.7 27.0 Block 4: Spray duration time sweep UG3622 –20 152.5 0 16.7 3.9 4.2 6.1 7.5 5.3 40.4 38.7 21.8 16.5 15.2 14.9 12.8 9.3 2.3 9.7 6.6 8.2 8.8 18.7 22.4 31.5 UG3624 –20 152.5 0 16.7 3.9 4.2 6.1 7.5 5.3 40.5 39.0 21.9 16.7 15.4 14.9 12.3 8.7 –0.1 9.0 6.5 8.1 8.7 18.8 22.6 31.5 Block 5: AOA sweep at T = –15 °C and U = 207 knots UG3600 –15 207 0 9.9 3.1 3.3 4.4 7.5 5.3 17.8 16.0 7.4 5.7 5.9 6.3 5.2 3.1 –1.8 3.2 0.2 0.7 1.6 13.4 16.7 24.8 UG3601 –15 207 2 9.9 3.1 3.3 4.4 7.5 5.3 19.3 18.3 10.5 7.7 7.2 7.3 6.5 4.1 –2.1 3.7 1.0 1.1 2.0 14.0 17.0 23.3 UG3597 –15 207 4 9.9 3.1 3.3 4.4 7.5 5.3 21.9 20.1 18.5 13.5 9.6 8.2 6.9 4.4 –2.1 4.0 1.4 1.4 2.3 13.9 16.8 21.7 UG3623 –15 207 4 9.9 3.1 3.3 4.4 7.5 5.3 23.0 20.6 19.5 14.6 10.4 8.8 7.8 5.1 –1.2 4.6 2.0 2.0 2.7 14.7 17.7 22.7 Block 6: AOA sweep at T = – 20 °C and U = 152.5 knots UG3611 – 20 152.5 0 9.9 3.1 3.3 4.4 7.5 5.3 18.1 17.1 8.2 6.2 6.2 6.5 5.1 2.3 – 4.9 2.3 – 0.5 0.1 1.6 15.9 20.3 30.2 UG3610 – 20 152.5 2 9.9 3.1 3.3 4.4 7.5 5.3 21.6 20.1 13.7 9.2 7.8 7.4 5.7 2.9 – 4.4 2.9 0.1 1.0 2.3 16.2 20.6 28.0 UG3609 – 20 152.5 4 9.9 3.1 3.3 4.4 7.5 5.3 23.5 21.4 21.8 18.2 12.9 9.7 7.0 3.8 – 2.5 4.0 0.7 1.5 2.8 16.2 20.3 25.4 UG3636 – 20 152.5 4 9.9 3.1 3.3 4.4 7.5 5.3 24.1 21.6 22.1 18.7 13.3 10.1 7.5 3.9 – 2.9 4.0 0.9 1.7 2.8 16.5 20.8 26.2

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52. Bartkus, T. P., Struk, P. M., and Tsao, J.-C., “Development of a Coupled Air and Particle Thermal Model for Engine Icing Test Facilities,” SAE International Journal of Aerospace, Vol. 8, No. 1, 2015, pp. 15-32, SAE Journal Paper 2015-01-2155.

53. Brunner, C. E., Kiefer, J., Hansen, M. O., and Hultmark, M., “Study of Reynolds number effects on the aerodynamics of a moderately thick airfoil using a high-pressure wind tunnel,” Exp Fluids 62, 178 (2021).

NASA/CR-2026000820 70

Overview

Appendix A provides nominal locations of surface mounted thermocouples (Table A.1), internally located View in PDF

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· · · · · · · · · · ·

· ·

Flow T301

71.8 in

· · · · · · · · · · · · ·

· ·

·

· · · · · · · · · · · ·

62.6 in

3.0 Addressing IRT Reference Pressure Issue Impacts

4.0 Aerodynamic Tests

4.1 Aerodynamic Test Objectives and Test Conditions

4.2 Ceiling Gap Flow Impact Investigation

4.3 Angle of Attack and Airspeed Sweeps

4.4 Comparison of 2023 to 2022 Measurements

4.5 Stagnation Point Inspection

5.0 Supercooled Liquid Icing Tests

5.1 Supercooled Liquid Icing Test Objectives and Test Matrix

5.2 Testing Procedures—Scanning and Weighing of Ice Mass

Ice on

Struts &

Casing

Weighed

10 in

8 in

Scanned

5.3 Total Air Temperature Sweep

0 A B

B A

C D

A B

D C

5.4 Spray Duration Time Sweep—Rime Ice Conditions

B A

-8 D C

B A

C D

5.5 Spray Duration Time Sweep—Glaze Ice Conditions

A B

B A

D C

A B

C D

5.6 Cloud Median Volumetric Diameter Sweep

A B

B A

D C

5.7 Angle of Attack Sweep

A

B

C

D

AOA = 0 ° AOA = 4 °

A B

Run ID# UG3589 Run ID# UG3634

248.7 g total 227.5 g total

Forward Forward

Aft

Aft

B A

D C

A B

C D

6.0 Ice Crystal Icing Tests

6.1 Ice Crystal Icing Test Objectives and Test Matrix

6.2 Testing Procedures—Scanning and Weighing of Ice Mass

8 in

Flow

Flow

Flow

6.3 Block 1: Repeat of 2022 Test Conditions at T = –15 °C

Flow

6.4 Block 2: Repeat of 2022 Test Conditions at T = –20 °C

Flow

6.5 Block 3: Heater Surface Heat Flux Evaluation

6.6 Block 4: Spray Duration Time Sweep

A

Appendix A provides nominal locations of surface mounted thermocouples (Table A.1), internally located

Appendix A.—Supplemental Information on