An Assessment of the SEA Multi-Element Sensor for Liquid Water Content Calibration of the NASA GRC Icing Research Tunnel

Document

An Assessment of

the SEA Multi - Element Sensor

for Liquid Water Content Calibration

of the NASA GRC Icing Research Tunnel

Laura E. Steen – Sierra Lobo, Inc.

Robert F. Ide – Sierra Lobo, Inc.

Judith F. Van Zante – NASA Glenn Research Center Cleveland, Ohio International Icing Conference 2015, Prague June 25, 2015 HX5 Sierra LLC National Aeronautics and Space Administration www.hxfive.com www.nasa.gov www.sierralobo.com Introduction:

• The NASA Glenn Icing Research Tunnel (IRT) is a facility that

is heavily utilized for development/certification of aircraft

ice protection systems and icing research.

• Data from the IRT has been accepted by the FAA, EASA, CAA, and

JAA in support of manufacturers’ icing certification programs.

• The IRT had been using an Icing Blade technique to measure

cloud liquid water content since 1980.

• The IRT conducted testing with Multi - Element sensors from

2009 to 2011 to assess performance . These tests revealed

that the Multi - Element sensors showed some significant

advantages over the Icing Blade .

• Results of these and other tests are presented here.

Outline:

• Facility Description (IRT) • Comparisons of Multi -

Element Sensor to Blade

• Description of the Multi -

• Varying water content

Element Sensor

• Varying speed

• Components

• Varying drop size (Large

• Physics (theory of operation)

drops, SLD)

• Processing Multi - Element data

• Conclusions:

• Description of the Blade

• Strengths of Blade

• Measurement Principles

• Limitations of Blade

• Ludlam Limit

• Strengths of Multi - Element

• Limitations of Multi - Element

Test Facility

• Test section size: 6 ft. x 9 ft. (1.8 m x 2.7 m) • Calibrated MVD range: 14 – 270 μm • All LWC & MVD calibration measurements are • Calibrated LWC range: 0.15 – 4.0 g/m made in the center of the test section (function of airspeed) • LWC uniformity is ± 10% for the central 4 ft x 6ft • Two types of spray nozzles: • Calibrated test section airspeed range: 50 – 325 kts • Standards = higher flow rate • Air temperature: - 40 degC static to +20 degC total • Mod1 = lower flow rate

The Multi - Element Sensor

From Science Engineering Associates, Inc.

• Commonly known as “the Multi - Wire”

• Typical Multi - Wire shrouds contain 3

sensing elements of various sizes

• Different element types are designed for Heated better response to different conditions stem & shroud • Elements vary in diameter and in shape • IRT typically uses just the TWC element for LWC calibration 1 in.

2.54 cm

• A compensation wire is located behind

central element

• Shielded from impinging liquid/ice water Sensing • measures changes coming only from elements airspeed, air temperature, air pressure, and relative humidity

Multi - Element Sensor

Theory of Operation

• A voltage is applied across each of the elements to maintain them at a temperature of 140 degC • Elements are cooled by convection and impinging water • Data system records the power required to maintain each element at constant temperature.

• The compensation wire is shielded to stay dry • Changes in the comp wire during a spray are reflected in the calculated water content • The recorded powers are used to calculate liquid water content: P = P – ( offset + slope * P ) elem,wet elem,tot comp,dry Subtract off cooling from dry air, correlated to comp wire Conversion factor 𝟓 𝑷 ( 𝒘𝒂𝒕𝒕𝒔 ) ∗ 𝟐 . 𝟑𝟖𝟗 × 𝟏𝟎 𝒆𝒍𝒆𝒎 , 𝒘𝒆𝒕 𝑳𝑾𝑪 = 𝒄𝒂𝒍 𝒄𝒂𝒍 𝒎 𝑳 + 𝟏 . 𝟎 𝑻 − 𝑻 ∗ 𝑻𝑨𝑺 ∗ 𝒍 𝒎𝒎 ∗ 𝒘 𝒎𝒎 𝒆𝒗𝒂𝒑 𝑶 𝒆𝒗𝒂𝒑 𝒂𝒎𝒃𝒊𝒆𝒏𝒕 𝒆𝒍𝒆𝒎 𝒆𝒍𝒆𝒎 𝒈 𝒈 ∗ 𝑪 𝒔 Amount of energy required to raise the drop temp to Sample volume of evaporative temperature and then evaporate it ( cal /g) sensing element (m /s) Source: the SEA User’s Manual

Multi - Wire Data Processing

Multi - Wire data trace, showing all 4 sensing elements Multi - Wire Data Trace at 100 kts , 14 μm Water Content on1/31/2012 at16:1:33, MVD=14  m, V=99.1 kts, Mod1 nozzles 0.6 TWC 0.5 Multi - Wire Data processing: 0.4

• IRT uses only the water )

content values from the TWC

0.3

element

0.2

• A comparison of the different

elements is beyond the scope of water content (g/m

0.1

this presentation

• In - house MATLAB code

averages and tares the

-0.1 -20 0 20 40 60 80 100 120 140 160

recorded values

2.2

• Code also flags data

Comp Wire Power Output comp wire

irregularities

spray start/end 2.1

• Measured TWC is corrected

for collection efficiency* 1.9

power output (watts) 1.8 -20 0 20 40 60 80 100 120 140 160 Time after spray start (sec) *3D collection efficiency: Rigby, D.L., Struk, P.M., and Bidwell, C., “Simulation of Fluid Flow and Collection Efficiency for an SEA th Multi - Element Probe,” 6 AIAA Atmospheric and Space Environments Conference, AIAA - 2014 - 2752, 2014.

The Icing Blade

• Simple piece of stainless steel: 1710 ∗ 𝑑

1/8” x 6” x 3/4”

𝐿𝑊𝐶 = 𝑉 ∗ 𝑡 ∗ 𝐸 𝑏 • 3.175 mm x 154.2 mm x 19.05 mm

• Was the standard measurement for d = ice thickness (mm)

V = tunnel airspeed ( kts )

all LWC calibrations in the IRT from

t = spray time (sec)

1980 to 2011

E = Collection efficiency b (calculated, function of

• Ice Accretion: Requires Rime Ice

airspeed, air density, • Tunnel total air temp of - 18 to - 20 degC & drop size) 1710 = constant — contains • Adjust spray time to collect approx.

unit conversions and 0.15 in. ( 3.8 mm) of ice.

an assumed ice density (12 ≤ t ≤ 200 sec) of 0.88 • Width of ice is measured (< 0.200 in., or 5mm) to make sure changes in collection efficiency are minimal

• 3 measurements (1 in. apart) — use

the median value

The Ludlam Limit ( for the blade)

• Ludlam Limit : the supercooled water impingement rate above which not all impinging water will freeze for a Ludlam Limit given air temperature and airspeed (impingement rate above which the measured LWC is reduced) Assuming Blade temp is at Tstat 3.5 • Water impingement rate is a function of the airspeed, LWC, Assuming Blade temp is at Ttot & Collection Efficiency 3 2.5 • Stallabrass applied Ludlam’s work to derive the Ludlam th limit for a 1/10 inch diam. rotating cylinder. We used his data to calculate the limit at - 20 degC 1.5 th Consider: We have a 1/8 in. Blade, th not a 1/10 in. rotating cylinder. Ludlam Limit (g/m3) 0.5 • Collection Efficiency : 0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 • We have data that shows the collection efficiency of the th th Airspeed (kts) 1/8 inch blade is within 2% of that of the 1/10 inch cylinder Figure: Ludlam limit as a function of airspeed for th • Temperature : Stallabrass used static air temperature. a 1/10 inch (2.49 mm) diam. cylinder and two temperature constraints [data from Stallabrass ] • In the IRT, icing blade tests are conducted at a total temperature between - 18 and - 20 degC .

• The blade temp is somewhere between static and total Stallabrass , J. R., “An Appraisal of the Single Rotating Cylinder Method of Liquid Water Content Measurement,” National Research Council Canada Internal Report, LTR - LT - 92, 1978.

Comparing Multi - Wire vs. Blade

• Thorough comparison had to be done before we could

switch LWC calibration instruments.

• The Multi - Wire has obvious advantages over the B lade in

terms of:

• Temperature  the Blade requires hard rime conditions

• Test efficiency  can collect 30 conditions/day with Blade ,

vs. 50 conditions/day with Multi - Wire

• Spray time  not restricted, can capture real - time trends

• We want to see how the two instruments compare, varying:

• Liquid water content (LWC)

• Airspeed

• Drop size (MVD)

Multi - Wire vs. Blade,

with respect to Liquid Water Content

• For these points:

LWC comparison, MVD=20 μ m , V=150 kt

2.5 • Airspeed = 150 kts • MVD = 20 μm 2.0 • T = - 20 degC (blade) tot ) • T = - 10 degC (multi - wire) tot 1.5

• For these conditions, the

Wire LWC (g/m 1.0 -

Ludlam limit is 1.8 g/m if we

Mod1 nozzles Multi

use the total temp, and 2.2 if

Standard Nozzles 0.5 1:1 we use the static temp.

+/-10%

0.0 • This plot shows the water

0 0.5 1 1.5 2 2.5

3 contents match until the LWC

Blade LWC (g/m )

approaches or surpasses the

Ludlam Limit

Multi - Wire vs. Blade,

with respect to Airspeed

Blade & Multi - wire LWC vs. Airspeed (MVD = 20 μm) • Airspeed sweeps for two nozzle sets, 4.5 MVD=20 μm Standard nozzles, Multi-wire 4.0 Standard nozzles, Blade • Standard nozzles are higher water Mod1 nozzles, Multi-wire flow, Blade testing requires shorter Mod1 nozzles, Blade spray time.

3.5 Ludlam Limit, assuming Blade at Tstat ) • Plotted alongside Ludlam limit curve fit Ludlam Limit, assuming Blade at Ttot 3.0 shown on previous slide • Limit for a temperature of - 20 degC 2.5 • The Mod1 nozzles show good 2.0 agreement between the MW and the blade, even at high airspeeds 1.5 Liquid Water Content (g/m • But at higher impingement rates (LWC x 1.0 airspeed x Collection Efficiency), the blade measures lower than the MW 0.5 0.0 0 50 100 150 200 250 300 350 400 Test Section Airspeed (kts) Multi - Wire vs. Blade,

with respect to Drop Size (MVD)

Multi - wire vs Blade LWC, at 100, 150, and 250 kts

Nozzle air pressure = 2 psig Nozzle air pressure = 5 psig Nozzle air pressure = 30 psig 2.0 2.0 2.0 100 kt 1.5 ] 1.5 1.5 3 150 kt ) ) 3 100 kts 1.0 1.0 250 kt 1.0 150 kts LWC (g/m LWC (g/m 0.5 0.5 0.5 250 kts Water Content [g/m 0.0 0.0 0.0 10 20 30 40 50 0 50 100 150 0 50 100 150 200 250 MVD [ μ m ] MVD ( μ m ) MVD ( μ m ) • As drop size increases, Blade measures lower than Multi - Wire.

But is this an effect of increasing drop size or of increasing LWC?

• We will try plotting this a different way…

Multi - Wire vs. Blade,

with respect to Drop Size (MVD ) (part 2)

100 knots 250 knots 150 knots 2.0 2.0 2.0 Ludlam limit Ludlam limit ) ) ) 3 3 1.5 1.5 1.5 Ludlam limit LWC (g/m LWC (g/m 1.0 LWC (g/m 1.0 1.0 Wire Wire Wire - - - 1:1 0.5 0.5 0.5 Multi Multi Multi +10% -10% 0.0 0.0 0.0 0 0.5 1 1.5 2 0 0.5 1 1.5 2 0 0.5 1 1.5 2 3 3 Blade LWC (g/m ) Blade LWC (g/m ) Blade LWC (g/m ) • For smaller drop sizes at all velocities, there is an LWC limit at which the Blade MVD : 14 – 50 μm measures lower than the Multi - Wire, even for MVD’s below 50 μm.

50 – 125 μm • For larger drop sizes, the Ludlam limit can no longer account for the roll - off we see 125 – 250 μm from the Blade. We suspect that we have an added problem due to mass - loss (splashing?) at larger drop sizes.