National Aeronautics and Space Administration
Ice Shape Analysis of an eVTOL Propeller in Forward
Flight at the NASA Glenn Icing Research Tunnel
Paul H. von Hardenberg
Curtis A. Flack
NASA Glenn Research Center
David L. Rigby
HX5 LLC
AIAA AVIATION FORUM th nd July 29 – August 2 , 2024 www.nasa.gov This is the work of the US Government and is not subject to copyright protection.
National Aeronautics and Space Administration
Background
PROBLEM While icing engineering tools and methods for means of compliance are fairly mature for existing legacy aircraft, there are no accepted icing engineering tools specifically developed and rigorously tested for AAM class vehicles.
OBJECTIVE Develop experimental and computational icing simulation capabilities for eVTOL vehicles.
APPROACH NASA Tiltwing Concept Vehicle • Acquire experimental ice shapes on non - proprietary propeller/rotor geometries for (cruise configuration) code validation and development.
• Establish best practices and scaling methodologies for conducting icing tests on rotating geometries.
• Acquire experimental shedding data to support development of ice shedding prediction capabilities.
ACCOMPLISHMENTS • Successfully completed two test entries of a generic eVTOL propeller in the Icing Research Tunnel in 2023 and 2024.
• Acquired ice shapes, propeller performance degradation, and high - speed images of shedding events.
This presentation and corresponding paper provides an analysis of the ice shape data acquired during the 2023 test only.
AAM Propeller Test Stand Installed in Icing Research Tunnel (IRT) www.nasa.gov 2 National Aeronautics and Space Administration
Test Article and Instrumentation
MOTOR FEATURES • Power: 34 kW (cont.), 60 kW (peak) • Torque: 52 Nm (cont.), 100 Nm (peak) TEST STAND FEATURES • Adjustable axis of rotation for non - axial flow • 6 - axis load cell for torque and thrust measurements MEASUREMENT CAPABILITIES • 3D ice shape documentation • Ice mass measurements • High speed imaging for capturing ice shedding events • Light strobing for real - time ice growth monitoring • Torque and thrust measurements • Motor current and voltage measurements
AAM Propeller Test Stand
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Propeller Geometry
Chord Distributions PROPELLER SPECIFICATIONS • Three propellers of diameters 24, 28, and 36 inches.
• Twist and chord distributions inspired by the NASA Computationally Optimized Proprotor (COPR)*.
• NACA 0012 airfoil • Geometrically scaled from a radial location of r/R = 0.40 and outward.
• Spinner not scaled with propeller size.
Ø36” Twist Distributions Ø28” Diameter = Ø24” *Zawodny et al., NASA TM 20220015637, NASA Langley Research Center, 2023 www.nasa.gov 4 National Aeronautics and Space Administration
Test Conditions
OPERATING CONDITIONS
Blade Helical Tip Tunnel Speeds Advance Diameters Speeds (knots) Ratios (in) (Mach) 24, 28, 36 87 - 130 0.20 - 0.31 2.3 – 2.7
CLOUD CONDITIONS
Freestream MVD LWC NOTE: Total Temp.
(μm) (g/m ) • Propeller in axial flow configuration (˚C) • Constant RPM for duration of spray 0.55, 0.65, 15, 30, 80 - 3 to - 15 1.20 • 28” propeller accounted for 39 of the 45 total test runs www.nasa.gov 5 National Aeronautics and Space Administration
Ice Shape Repeatability
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Effect of Freestream Total Air Temperature
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Effect of Temperature (cont.)
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Effect of Temperature (cont.)
𝒕 = − 𝟑 . 𝟎°𝑪 ∞ , 𝟎 ∗
𝑛 = 0 . 51
𝒕 = − 𝟔 . 𝟎°𝑪 ∞ , 𝟎 ∗
𝑛 = 1 . 01
𝒕 = − 𝟕 . 𝟓 °𝑪 ∞ , 𝟎 ∗
𝑛 = 1 . 26
𝒕 = − 𝟗 . 𝟎 °𝑪 ∞ , 𝟎 ∗
𝑛 = 1 . 49
𝒕 = − 𝟏𝟐 . 𝟎 °𝑪 ∞ , 𝟎 ∗
𝑛 = 1 . 94
𝒕 = − 𝟏𝟓 . 𝟎 °𝑪 ∞ , 𝟎 ∗
𝑛 = 2 . 37
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Effect of Icing Time ( 𝑛 = 1.0)
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Effect of Icing Time ( 𝑛 < 1.0)
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Effect of Icing Time
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Effect of MVD
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15 MVD 80 MVD
Reduction of concentration and Region of high concentration shadow zones Propeller Region of reduced or Shift in Root zero concentration impingement Spinner (shadow zone) limits Impingement Limits www.nasa.gov 14 National Aeronautics and Space Administration Effect of MVD cont.
+327% +171% +32% +23% www.nasa.gov 15 National Aeronautics and Space Administration
Scaling for LWC ( 𝑛 < 1.0)
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Scaling for Propeller Size
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Summary and Conclusion
• Ice shapes were generated on a non - proprietary eVTOL propeller in an
axial flow (forward flight) configuration in the Icing Research Tunnel.
• Ice shapes were reviewed for their repeatability, correctness of trends, and sensitivity to parameter variations.
• Icing similarity parameters were calculated at discrete radial locations
– Qualitatively useful and followed predicted trends.
– Appeared to overestimate freezing fraction.
• Fixed wing scaling methods were applied to the propeller with promising
results.
– More data is needed over a wider range of conditions and propellers sizes to
provide confidence in the scaling method.
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Acknowledgments
This work was funded by the NASA R evolutionary V ertical L ift
T echnology ( RVLT ) project.
Special thanks to the NASA Glenn Icing Branch and the IRT
personnel for their invaluable support throughout this effort.
Contact Information
Paul H. von Hardenberg
NASA Glenn Research Center
paul.h.vonhardenberg@nasa.gov
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Backup Slides
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Calculation of Icing Similarity Parameters
Key Icing Similarity Parameters
• Icing similarity parameters were calculated at
stagnation for discrete radial locations along the blade.
∗
• NOTE: Freezing Potential 𝑛 = Freezing Fraction 𝑛
with no upper limit.
Example Freezing Potential vs Span Distributions www.nasa.gov 21 National Aeronautics and Space Administration
Calculation of Icing Similarity Parameters
Table 1: Description of Important Icing Similarity Parameters • Icing scaling methods for unprotected fixed airfoils have been well established [1, 2].
• There remains to be an accepted and rigorously tested icing scaling method for rotating airfoils.
• Application of fixed - wing icing scaling methods to rotating airfoils offers a good starting point.
They key icing similarity parameters (Table 1) can be • Freezing fraction has a theoretical upper estimated by substituting the effective velocity , 𝑽 , 𝒆𝒇𝒇 limit of 𝑛 = 1.0 for the freestream velocity , 𝑽 , during the derivations ∞ of those parameters.
• However, calculation of 𝑛 can sometimes produce values greater than 1.0 For this study, the effects of propeller induction were • The unbounded value of 𝑛 will be presented ignored such that: which will hereinafter be referred to as the ∗ Freezing Potential, 𝒏 𝟐 𝟐 𝑽 ≈ 𝑽 + 𝝎𝒓 𝒆𝒇𝒇 ∞ www.nasa.gov 22 National Aeronautics and Space Administration Effect of MVD cont.
15 MVD 30 MVD 80 MVD (high pressure side) www.nasa.gov 23