NASA/TM--2001-210689

U.S. ARMY

RESEARCH LABORATORY

J

_7 t _-",f //_/ 1t : "ft

1

"-3-'-' I ::9 i I/

Icing Cloud Calibration of the NASA

Glenn Icing Research Tunnel

ARL-TR-2383

AIAA-2001-0234

Robert F. Ide

U.S. Army Research Laboratory, Glenn Research Center, Cleveland, Ohio

John R. Oldenburg

Glenn Research Center, Cleveland, Ohio

March 2001
The NASA STI Program Office... in Profile

Since its founding, NASA has been dedicated to

the advancement of aeronautics and space

science. The NASA Scientific and Technical

Information (STI) Program Office plays a key part

in helping NASA maintain this important role.

The NASA STI Program Office is operated by

Langley Research Center, the Lead Center for

NASA's scientific and technical information. The

NASA STI Program Office provides access to the

NASA STI Database, the largest collection of

aeronautical and space science STI in the world.

The Program Office is also NASA's institutional

mechanism for disseminating the results of its

research and development activities. These results

are published by NASA in the NASA STI Report

Series, which includes the following report types:

TECHNICAL PUBLICATION. Reports of

completed research or a major significant

phase of research that present the results of

NASA ptx,grams and include extensive data

or tht_*retical analysis. Includes compilations

of significant scientific and technical data and

information deemed to be of continuing

reich.nee value. NASA's counterpart of peerreviewed formal professional papers but

ha._ k._s stringent limitations on manuscript

length and extent of graphic presentations.

TECHNICAL MEMORANDUM. Scientific

and tt,:hnical findings that are preliminary or

of spt_:ialized interest, e.g., quick release

report_, working papers, and bibliographies

that contain minimal annotation. Does not

contain extensive analysis.

CONTRACTOR REPORT. Scientific and

technical findings by NASA-sponsored

contractors and grantees.

CONFERENCE PUBLICATION. Collected

papers from scientific and technical

conferences, symposia, seminars, or other

meetings sponsored or cosponsored by

NASA.

SPECIAL PUBLICATION. Scientific,

technical, or historical information from

NASA programs, projects, and missions,

often concerned with subjects having

substantial public interest.

TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientific

and technical material pertinent to NASA's

mission.

Specialized services that complement the STI

Program Office's diverse offerings include

creating custom thesauri, building customized

data bases, organizing and publishing research

results.., even providing videos.

For more information about the NASA STI

Program Office, see the following:

• Access the NASA STI Program Home Page

at http://www.sti.nasa.gov

• E-mail your question via the Internet to

help@sti.nasa.gov

• Fax your question to the NASA Access

Help Desk at 301-621-0134

• Telephone the NASA Access Help Desk at

301-621-0390

Write to:

NASA Access Help Desk

NASA Center for AeroSpace Information

7121 Standard Drive

Hanover, MD 21076
NASA / TMm2001-210689

U.S. ARMY

RESEARCH LABORATORY

Icing Cloud Calibration of the NASA

Glenn Icing Research Tunnel

Robert F. Ide

U.S. Army Research Laboratory, Glenn Research Center, Cleveland, Ohio

John R. Oldenburg

Glenn Research Center, Cleveland, Ohio

ARL-TR-2383

AIAA-2001-0234

Prepared for the

39th Aerospace Sciences Meeting and Exhibit

sponsored by the American Institute of Aeronautics and Astronautics

Reno, Nevada, January 8-11, 2001

National Aeronautics and

Space Administration

Glenn Research Center

March 2001
Acknowledgments

I wish to thank the IRT crew for the excellent support I received during the 3-plus months of testing required to

perform this cloud calibration. Without their energetic and helpful support, that length of time would

have seemed even longer than it did.

Trade names or manufacturers' names are used in this report for

identification only. This usage does not constitute an official

endorsement, either expressed or implied, by the National

Aeronautics and Space Administration.

Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

Price Code: A03

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

Price Code: A03

Available electronically at http: / / gltrs.grc.nasa.gov / GLTRS
ICING CLOUD CALIBRATION OF THE NASA GLENN ICING RESEARCH TUNNEL

Robert F. Ide

U.S. Army Research Laboratory

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

John R. Oldenburg

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

The icing research tunnel at the NASA Glenn Research

Center underwent a major rehabilitation in 1999,

necessitating recalibration of the icing clouds. This

report describes the methods used in the recalibration,

including the procedure used to establish a uniform

icing cloud and the use of a standard icing blade

technique for measurement of liquid water content. The

instruments and methods used to perform the droplet

size calibration are also described. The liquid water

content/droplet size operating envelopes of the icing

tunnel are shown for a range of airspeeds and compared

to the FAA icing certification criteria. The capabilities

of the IRT to produce large droplet icing clouds is also

detailed.

Introduction

The icing research tunnel (IRT) at NASA Glenn

Research Center underwent a major rehabilitation in

1999. The leg upstream of the test section, which

contains the heat exchanger, was completely removed.

The reconstruction widened this leg from its former

29 feet to 42 feet to allow a flat-faced heat exchanger

adequate space to replace the former "W" shaped heat

exchanger, which had been operational since 1944. New

aerodynamic turning vanes were installed in the comer

between the fan and the heat exchanger. These vanes

both turn the flow and also expand the flow from the

upstream 29-foot width to the new 42-foot width. New

vanes were also installed in the comer between the heat

exchanger and the contraction. These vanes contract the

flow around the comer back to the 29-foot width. Exit

guide vanes were also installed downstream of the fan.

These changes to the tunnel were made for two primary

reasons. The first was to improve flow quality in the

test section. The second was to replace the heat

exchanger which was experiencing increased leak rates

after it's more than 50 years of service.

Further description of the changes made during the

rehabilitation is contained in reference 1. Evaluations of

the flow quality improvements realized by these tunnel

modifications are contained in reference 2 and 3.

The changes in the icing tunnel necessitated a

recalibration of the icing clouds. The recalibration

included: (l) establishment of spray nozzle locations in

the spray bars to generate a uniform icing cloud in the

test section; (2) measurement of the droplet size

distributions and of the liquid water content of these

clouds to determine the effects of spray air pressure,

water flow rate and tunnel airspeed.

This paper describes the methods used in the

recalibration of the icing tunnel and presents the results

of these calibrations.

Facility Description

A plan view of the former IRT loop and the new IRT

loop are shown in figure 1. The tunnel is of the closedloop design. The test section is 9 feet wide, 6 feet high

and is approximately 20 feet long. The tunnel fan is

powered by a 5000 horsepower electric motor, which can

generate maximum airspeeds of almost 350 knots. The

tunnel now contains a fiat-faced heat exchanger, which

allows testing over a temperature range of 40°F to -20°F.

NASA/TM--2001-210689 1
Thetunnelwaterspraysystemconsistsof 10 spray

bars, which are located in the low-speed section of the

tunnel just upstream of the contraction. Each spray bar

has positions for up to 55 spray nozzles. Each nozzle

location is supplied by two independent water

manifolds through individually controllable electrically

activated solenoid valves. Two different nozzles are

used to increase the LWC range of the tunnel. They are

referred to as the Standard and Mod l nozzles. They are

both of the same air-assist configuration, the only

difference being the diameter of the water tubes. The

Standard nozzles have a water tube diameter of

0.025 inches; the Mod ! nozzles have a water tube

diameter of 0.0155 inches. The nozzles used in the

spray system have matched water flow coefficients to

within _+5 percent.

Purpose of Calibration

Calibration of the icing clouds consists of three parts.

The first part is to determine the locations of the spray

nozzles and the number of nozzles required to generate

as uniform an icing cloud as possible in the tunnel test

section. The next two parts are to make measurements

of the droplet sizes and liquid water contents (LWC) at

many different combinations of spray air and water

pressures.

The droplet size and LWC data are used to determine

the relationship of these parameters to the spray air and

water pressures. During actual icing tests the droplet

size and LWC are not measured. Instead, the spray air

and water pressures are calculated for the desired

droplet size and LWC conditions.

The operating ranges of the tunnel are as follows:

Airspeed: 50 to 300 knots

Air Temperature: Ambient, to -20°F

Spray Air Pressure: 10 to 70 psig

Spray AP: 5 to 150 psid (Standard nozzles)

5 to 250 psid (Mod 1 nozzles)

The spray Ap is the water pressure minus the air

pressure. This is the parameter that is used for

calculations of droplet size and LWC since the water

flow rate is proportional to AP °5.

Icing Cloud Uniformity

The term icing cloud uniformity really refers to the

degree of liquid water distribution across the tunnel test

section. It is desirable that the liquid water within the

cloud be uniformly distributed from wall to wall and

from floor to ceiling. However, due to limitations in

possible nozzle locations within the spray bar system

and variations in airflow (wakes, corner vortices, flow

angularity, etc.) the icing cloud generated in a tunnel

always has variations. The goal of establishing nozzle

locations to in turn establish a uniform cloud is to

generate as large a cloud as possible with as little

variation as possible. The current criteria for a

"uniform" icing cloud is that variations in LWC of

+ 20 percent are acceptable.

The first step in trying to establish a uniform icing

cloud was to determine where the spray from each area

of the spray bars ended up in the test section. A six-foot

by six-foot stainless steel grid was place in the test

section, centered horizontally within the 9-foot wide

test section. The grid, a picture of which is shown in

figure 2, has six-inch vertical and horizontal spacing.

The tunnel was cooled to 0°F and the airspeed was set

to 150 knots. Once the tunnel had stabilized at this

temperature and airspeed, water spray was initiated

from widely spaced spray bars. Ice was allowed to

accrete on the grid for several minutes. The peak of the

ice accretion as well as the width of the iced band was

then documented.

This test was repeated for all of the spray bars. It was

also performed for 16 (vertical) columns of nozzles. It

was then repeated for the other set of nozzles.

Figure 3 shows the lines of peak ice accretion on the

grid for all spray bars. The dashed lines on this figure

are the geometric projections of the spray bar locations

into the test section. It can be seen in this figure that the

spray along the vertical centerline is compressed toward

the center of the tunnel. These patterns are similar to

the patterns for the previous heat exchanger

configuration.

Figure 4 shows the patterns of icing generated from the

nozzle column tests. The dashed lines in this figure are

the patterns generated from similar tests with the

previous heat exchanger. It can be seen that there is

considerably less distortion of the spray columns with

the new heat exchanger particularly on the left side

(inner wall) of the test section. This decrease in

distortion is attributable to the elimination of the small

heat exchanger section of the old heat exchanger, which

severely distorted the flow.

Following this test a uniform pattern of spray nozzles

was installed in the spray bars. The tunnel was

stabilized at an airspeed of 150 knots and a temperature

of 0°F. All nozzles were activated and ice was allowed

to accrete on the grid. The ice thickness was then

measured at 6-inch vertical intervals, starting 3 inches

from the test section ceiling. These data was then

ratioed to the average of two values near the center of

NASA/TM--2001-210689
the test section and were then used to construct a

contour plot of the LWC uniformity. This plot along

with the results from the single spray bar/single column

tests was used to guide the process of adding or

changing nozzle locations to improve the cloud

uniformity. Approximately 30 iterations of nozzle

position changes an acceptable uniformity pattern was

established. The process of optimizing the cloud

uniformity involved a considerable amount of trial and

error and was very time consuming.

During the process of establishing a uniform icing

cloud with the Mod 1 nozzles, it was found that the

nozzle spacing was much more regular than the nozzle

array used with the former heat exchanger. The flow

patterns caused by of the former heat exchanger

allowed only one set of nozzles to be installed at a time

since many of the same nozzle locations were required

by both nozzle sets. Given the more uniform pattern of

the Mod 1 nozzles, we decided to see if it was feasible

to install both the Mod 1 and Standard nozzles in the

spray bars at the same time, each set supplied by its

own water manifold.

Based on the Mod 1 nozzle locations, the Standard

nozzles were positioned between these locations, with

somewhat smaller spacing. After about 20 iterations of

changes in some Mod 1 and Standard nozzle positions,

the final nozzle positions for both nozzle sets were

established. The final nozzle arrays contained

150 Standard nozzles and 102 Mod 1 nozzles.

There is a major benefit to being able to have both

nozzle sets installed at the same time. Nozzle changeouts are not required to switch between the two nozzle

sets, permitting more flexibility is testing. Also the

productivity of the tunnel is improved since nozzles

changes took approximately four hours.

Figure 5 shows the contour plot of the LWC for the

Standard nozzles at an airspeed of 150 knots. The

contour intervals on this plot are in 10 percent bands.

The blue area represents values within + 10 percent of

the averaged center values. The green areas are low

spots and the red areas are high spots. It can be seen

from this plot that the cloud covers the whole grid area

and that most of the cloud is within the + 20 percent

allowable tolerance.

Figure 6 shows contour plots of the LWC cloud

uniformity of the Mod 1 nozzles for several airspeeds.

All of these tests were run at spray bar air pressures of

20 psig. At 100 knots (figure 6(a)) the icing cloud is

very uniform over the 4.5-foot vertical by 5-foot wide

central region of the test section. At 150 knots (figure

6(b)) more high and low spots are present within this

same area. As shown in figures 6(c) and 6(d), the

200 and 250 knot clouds have many scattered high and

low spots. These high and low areas are a result of

insufficient mixing of the spray from individual spray

nozzles, which is exasperated by increasing airspeed.

Note that in many cases the LWC transitions from a

20 percent high spot to a 20 percent low spot within a

distance of only 6 inches.

A test was run to see how higher nozzle air pressure

would effect the cloud mixing. The spray bar air

pressure was increased to 40 psig while maintaining the

same droplet size. The result of this test is shown in

figure 7, where it can be seen that when compared to

figure 6(b), mixing of the cloud was greatly improved.

Almost the whole central region of the cloud is

completely uniform.

For comparison with the new data figure 8 shows an

LWC uniformity plot generated before the icing tunnel

rehabilitation. The airspeed for this test was 217 knots.

When compared to figures 6(c) and 6(d) it can be seen

that the high and low spots in the new clouds are much

smaller than the rather broad areas of the old cloud.

This is again an indication that the spray from

individual nozzles is not well mixed.

The experiences with establishing a uniform icing cloud

point out a reality of icing tunnel work. Improving

aerodynamic characteristics can have an adverse effect

on the uniformity of the icing cloud.

Droplet Size Calibration

Two droplet sizing instruments were used in the droplet

size calibration of the icing research tunnel. These were

the Forward Scattering Spectrometer Probe (FSSP) and

the Optical Array Cloud Droplet Spectrometer Probes

(OAP). These are aircraft type instruments

manufactured by Panicle Measuring Systems, Inc. of

Boulder, Colorado.

The FSSP 4"5 was used to measure droplets with

diameters of 2 to 47 lam. In this instrument a laser beam

is used to illuminate single panicles as they traverse the

sample volume. The intensity of the forward scattered

light is measured to determine the particle size. Larger

particle have greater intensity. The instrument counts

each panicle passing through the laser beam and places

the count in one of 15 size bins. The nominal bin width

for the FSSP is 3 _un. Over time a number versus

panicle size histogram is obtained. A data analysis

program is used to convert the number histogram into a

volume histogram and to calculate other characteristics

of the droplet distribution such as the median volume

diameter.

NASA/TM--2001-210689 3
TheOAP5 was used to measure droplets with diameters

of 9.5 to 457.5 gtrn. This instrument uses a collimated

laser beam to illuminate particles creating a shadow,

which is magnified and projected onto a linear

photodiode array. The number of diodes shadowed

determines into which particle size bin the particle will

be placed. The diode spacing and the system

magnification determine the size definition of each size

bin. The nominal bin width for this OAP is 15 gtrn.

The particle sizing instruments were mounted in the

tunnel on the centerline of the test section one at a time.

The FSSP is shown in Figure 9. Each spray condition

(i.e., air pressure and water pressure) was set and

allowed to stabilize before a measurement was started.

The sample time used for the FSSP was 50 seconds and

the sample time for the OAP was 100 seconds.

Measurements were made with the FSSP first for all the

spray conditions, which covered the air pressure and

water pressure range of the facility. The OAP was then

used for those spray conditions where it appeared that

the FSSP had not captured the complete droplet size

distribution. Approximately 100 test conditions were

measured for the Standard nozzles and 150 test

conditions _ere measured for the Mod 1 nozzles.

Data Processing of Droplet Size Distributions

The median volume diameter (MVD) is used to

charactcrtzc the droplet size distribution. The MVD is

dcfincd a, the diameter where half of the volume of

water is coma,ned in droplets with diameters smaller

tot larger _than this diameter. To calculate a meaningful

median xolumc diameter (MVD), it is often necessary

to combine the droplet size distributions from more

then one instrument. The procedure used to calculate

the total xolumc xvas to calculate the total volume of the

droplets from the FSSP and to add to this the additional

volume of the droplets from the OAP that exceed the

range of thc FSSP. Thus in the overlap size region of

the FSSP and OAP the FSSP measurements are used.

This provides an effective droplet size range for the

OAP of 47 to 457.5 gtrn. Figure 10 shows an example of

the combined distributions from the FSSP and OAP.

This distribution is a droplet number distribution versus

droplet size that has been normalized by the

instruments" bin widths and sample volumes. The

square symbols are from the FSSP and the triangle

symbols are from the OAP. The two filled triangles are

the data from the OAP in the overlap region that are

discarded In this example, the two instruments combine

to produce a smooth continuous curve from 2 to

300 gtm with a large dynamic range in number density

of 1e 2to I e-5.

Figure 11 shows examples of cumulative volume

distributions for MVD values from 15 to 40 larn. These

curves are generated by calculating the percentage of

the total droplet volume contained in each size bin of

each insmmaent and then summing them. It can be seen

from these curves that as the MVD increases the droplet

size distribution becomes broader. Note that the 40 ktrn

MVD distribution has droplet diameters exceeding

200 wn.

Droplet Size Equations

The MVD data from the droplet size calibrations were

fit to an equation for each nozzle type so that the tunnel

cloud MVD can be directly calculated for any pair of

spray bar air pressure and water pressure settings.

These equations are valid over a range of air pressures

from 10 to 70 psig; AP range of 10 to 150 psid for the

Standard nozzles and 10 to 250 psid for the Mod 1

nozzles. The calculation of MVD is valid for MVD

values up to 50 txm.

For each nozzle type (Mod 1 and Standard) the MVD

data was tabulated as a function of spray bar Pair and

AP. A commercially available software program 6 was

used to fit these data using least-squares procedures to a

large number of candidate equations. These equations

were then ranked based on the root mean square error

(MSE). The top several ranked equations were

reviewed for both nozzle types in order to select the

best equation that could be used for both the Mod l and

Standard nozzle types. The equation has the following

form:

MVD = EXP (a + bx + cy + dx = + _ z + fi_x + gx

+ h), _ + iyZx + jyx z )

where x is the natural log of the air pressure in psig, and

y is the AP in psid. The coefficients a thru j for the Mod

1 and Standard are listed in Table 1. Figures 12 and 13

show these equations plotted as a function of MVD

versus AP for constant air pressure lines between 10

and 70 psig for the Standard and Mod 1 nozzles.

Liquid Water Content Calibration

A standard icing blade r was used to measure the liquid

water content in the center of the test section. The blade

is made of stainless steel and is 6-inches long, threefourths of an inch deep and one-eighth of an inch thick.

All tests were run at an air temperature of 0°F to insure

that the ice that formed on the thin eighth inch face

would have minimal width so that the blade collection

efficiency would not have to be adjusted.

NASA/TM--2001-210689
The collection efficiency, Eb, of the blade was

calculated for the full range of airspeeds and droplet

sizes used for this testing. The computer code used, the

FWG two-dimensional droplet trajectory code, 8 uses a

Hess-Smith panel code for the flowfield prediction and

a C. W. Gear stiff equation scheme to integrate particle

trajectories.

After the tunnel temperature and desired airspeed were

stabilized the water spray was turned on at the desired

air and water pressure for a predetermined time. The

thickness of ice on the blade was measured using a

chilled micrometer. The measured ice thickness,

exposure time and airspeed were used in the equation

below to calculate the liquid water content.

L WC -

Cx p,,.,, xAS 4.34 x 104 xAS

E axVxt E_xVxt

In this equation C is a unit conversion constant, p,¢¢ is

the density of ice which is assumed to be constant

(i.e., p_¢¢= 0.88), AS is the thickness of ice in inches, Eb

is the blade collection efficiency, V is the free-stream

airspeed in knots and t is the spray time in seconds.

The icing blade was used to measure liquid water

content values over a range of spray air pressures from

10 to 70 psig, airspeeds from 50 to 300 knots and

droplet sizes from 14 to 50 _m. It was known from past

experience that the liquid water content calibration is a

function of both air pressure and airspeed, that is:

LWC= K(f(_,_,V)x-- V

where AP is the spray bar water pressure minus the air

pressure and is proportional to the water flow rate.

The first series of tests involved varying the spray bar air

pressure while holding the airspeed and droplet size

constant. The results of these tests are shown in

figure 14 for both nozzle sets. It can be seen from this

plot that the liquid water content decreases as the air

pressure increases. There are two possible causes for this

decrease--droplet freeze-out and evaporation. Droplet

freeze-out is caused by the temperature decrease of the

compressed air as it undergoes an isentropic expansion at

the exit of the nozzles. 9,m Evaporation of some of the

water is also very possible since the air used in the spray

system is very dry, having a dew point of approximately

-50°F and is heated to a temperature between 165 and

190°F. And since the airflow increases with air pressure

an increase in evaporation would be expected with

increasing air pressure.

The next series of tests involved varying the airspeed

from 50 to 300 knots while holding the air and water

pressures and the droplet size constant. Figure 15 shows

the results of these tests, where it can be seen that a

natural log function generates a reasonable fit to the data.

The effect of droplet size was also investigated, but no

significant effects were found within the droplet size

(i.e., MVD) range of 14 to 50 _m.

The two equations for "K" generated from the air

pressure and airspeed tests were combined to generate

the calibration equations for each nozzle set. The final

equations are:

Standard Nozzles:

LWC = (14.2x LnV - 0.30x Pa,, - 13.0)x--

V

Mod I Nozzles:

LWC = (4.45 x LnV-O.O475x P_. -4.8)x--

V

Figure 16 shows a comparison of the LWC data taken

with the icing blade to the values calculated from the

equations above. Almost all of the data is within a

+ 10 percent band, indicating a reasonable fit of the

data by the equations.

Icing Cloud Operating Range

The results of the liquid water content and droplet size

calibrations were combined to establish the operating

envelopes of the spray system. Since the liquid water

content is a function of airspeed in the tunnel, these

operating envelopes are also a function of airspeed.

The goal of any icing tunnel is to be able to duplicate as

fully as possible the Federal Aviation Administration

(FAA) aircraft icing certification standards contained in

FAR Part 25, Appendix C. These icing envelopes are

shown in figure 17. The upper envelope is called the

maximum intermittent envelope applicable to flight in

cumulous clouds while the lower envelope, the

continuous maximum envelope, is applicable to flight

in stratus-type clouds.

Figure 18 shows the capabilities of the IRT at an

airspeed of 100 knots compared to the FAA icing

criteria. The figure illustrates that the IRT has the

capability to cover much of the higher LWC conditions

of the intermittent maximum envelope at the smaller

droplet size end but does a poor job of covering the

NASA/TM--2001-210689 5
lowerLWC rangeof the intermittentmaximum

envelopeatdropletsizesabove35lam.TheIRTatthis

speedcan duplicatevery little of the continuos

maximumenvelope.

Figure19showsthecapabilitiesof theIRTat an

airspeedof 300knots.Atthisairspeedit canbeseen

thattheIRTdoesabetterjobof duplicatingthelower

LWCvaluesofthecontinuousmaximumenvelopebut

cannotduplicatethehigherLWCvaluesat smaller

dropletsizesoftheintermittent maximumcriteria.

Thenumberof nozzlesin thespraybarscouldbe

adjustedtoexpandtheamountof overlapbetweenthe

tunnelcapabilitiesandtheFAAcriteria.However, any

changesin thenozzlearraywouldrequireadditional

liquidwatercontentcalibrations. Substantial changesin

thenumberof nozzlescouldhaveadetrimental effect

ontheclouduniformity. Thenumberofdifferentnozzle

arraysmustalsobebalancedagainsttheimpactofthe

productivityofthetunnel.

Anotherpossibleapproachofincreasingtheamountof

overlapbetweentunnelcapabilityandtheFAAcriteria

istouseadifferenttypeof spraynozzle.However, no

nozzlethatisclearlysuperiortotheNASAnozzleshas

beenfound.

Large Droplet Icing Clouds

The crash of an ATR-72 at Roselawn, Indiana in 1994

initiated a lot of interest in icing clouds not normally

considered in aircraft icing certification. These include

freezing drizzle and freezing rain. Customers have

requested NASA to generate icing clouds with much

larger droplets than previously required. In response to

customer demand, and lacking guidance from the FAA,

a small number of large droplet conditions were

established in the IRT.

The calibration methods for these conditions were

similar to those already described for the "normal"

icing conditions. The LWC of these large droplet

clouds was measured using a 1.5-inch diameter rotating

cylinder instead of the icing blade. It was felt that large

droplets might splash off the surface of the blade,

resulting in an under-estimation of the true LWC, and

that this was much more unlikely with a the rotating

cylinder.

Also an additional droplet-sizing instnunent was used.

The operation of this instrument is the same as the OAP

previously described but measures droplets with

diameters from 50 to 1500_'n.

Table 2 lists the large droplet conditions calibrated in

the IRT. Five large droplet conditions have been

established. The cloud uniformity and LWC were

determined for these 5 conditions at 3 airspeeds. It can

be seen from this table that as the airspeed is increased

the LWC decreases as expected. The cloud size also

decreases with increasing airspeed.

Figure 20 shows a contour plot of the cloud uniformity

of the 120 _ cloud at 200 knots. Note that the scale

for this plot differs from the contour plots previously

shown. The scale for this plot is in intervals of

20 percent, not 10 percent as previously used. It can be

seen from this plot that there exists a reasonably

uniform area around the center of the test section with

an approximate size of 4-feet high by 2.7-feet wide.

The droplet size distributions, in the form of cumulative

percent LWC curves, are shown in figure 21. These

curves indicate the very wide range of droplet diameters

that exit in these distributions. Note that the maximum

droplet diameters in these distributions are approaching

1000 _xrn or 1 mm.

Conclusions

A complete calibration of the IRT was performed

following the rehabilitation of the leg between the fan

and the test section. This calibration included

establishing nozzle locations to optimize the icing cloud

uniformity and performing extensive droplet size and

LWC measurements to generate a calibration relating

these measurements to the spray air and water pressures.

It was shown that, although the flow qualities of the

tunnel were greatly improved, the uniformity of the

icing clouds did not show similar improvement and

may have been degraded somewhat as a result of

reduced mixing.

A major advancement in tunnel capabilities was

attained as a result of the improved flow qualities. Both

the Standard and Mod 1 nozzles are now installed in the

spray bars at the same time, each set operated off

separate water manifolds. This results in much more

flexibility in running icing tests and increases the

productivity of the facility.

The large droplet icing capabilities of the IRT were

documented through measurement of the cloud

uniformity, droplet sizes and LWC values at several

airspeeds. It was shown that some very large droplets,

on the order of almost 1000 lam, can be generated and

delivered to the test section, although the uniform cloud

shrinks with increasing droplet size and airspeed.

NASA/TM--2001-210689
Recommendations

Methods of increasing the amount of mixing of the

icing sprays to improve the LWC uniformity in the test

section at high airspeeds and low spray air pressures

should be investigated. A method to generate more

mixing without adversely affecting the maximum

airspeed of the tunnel is desired.

Methods of increasing the LWC/MVD coverage of the

FAA icing test criteria contained in FAR Part 25

Appendix C should be investigated. This should include

considering the use of other types of spray nozzles.

References

I. Sheldon, D. et al., "Lessons Learned and Results

from the Construction Phase and Qualification Testing

of the Icing Research Tunnel Upgrades," AIAA-2001-

0231.

2. Gonsalez, J., Arrington, E., and Curry III, M., "Flow

Quality Surveys in the NASA Glenn Icing Research

Tunnel (2000 tests)," AIAA-2001-0232

3. Gonsalez, J., Arrington, E., and Curry III, M., "AeroThermal Calibration of the NASA Glenn Icing

Research Tunnel (2000 tests)," AIAA-2001-0233.

4. Dye, J.E. and Baumgardner, D., "Evaluation of the

Forward Scattering Spectrometer Probe i: Electronic

and Optical Studies," "'Journal of Atmospheric and

Oceanic Technology," Vol. 1, December 1984,

pp. 329-344.

5. Hovenac, E.A., "Droplet Sizing Instrumentation

Used for Icing Research: Operation, Calibration and

Accuracy," NASA CR-182293, August 1989.

6. TableCurve TM 3D v2.0.7 © 1996 AISN Software,

Inc, Jandel Scientific, San Rafael, CA.

7. Stallabrass, J.R., "An Appraisal of the Single

Rotating Cylinder Method of Liquid Water Content

Measurement," Canadian Research Council Report

LTR-LT-92, November 1978.

8. Frost, W., "Two-Dimensional Particle Trajectory

Computer Program," Interim Report for Contract

NAS3-22448, March 1982.

9. Marek, C.J. and Bartlett, C.S., "Stability Relationship

for Water Droplet Crystallization with the NASA Lewis

Icing Spray," NASA TM-100220, 1988: AIAA-88-

0289.

10. Lazeile, B.D., "'Conditions to Prevent Freeze-Out

During Atomization of Water Sprays for Icing Cloud

Simulation," D. Napier and Son Limited, Bedfordshire,

England, 1958.

NASA/TM--2001-210689 7
Table1.--Valuesforcoefficientsindropletsizeequations.

COEFFICIENT MOD 1 NOZZLES STANDARD NOZZLES

a 8.748044966 15.86986874

b -5.758889866 -13.19240311

c 0.138821237

d 1.698096143

0.972293768

4.129785202

e 4.86192E-05 0.001586357

f -0.067544202 -0.49291007

g -0.165992209 -0.416788168

h 8.85362E-08 1.70613E-07

I --2.14547E-05 -3.86283E-04

j 0.008648964 0.062787444

Table 2.--Super-cooled large droplet test conditions.

AIRSPEED MVD LWC

[kts] [um] (+6in)

100 70 0.86

100 100 0.95

100 120 0.98

100 175 1.52

100 270 0.99

150 70 0.63

150 100 0.67

150 120 0.65

150 175 0.96

150 27O 0.87

200 70 0.43

200 100 0.47

200 120 0.46

200 175 0.63

200 270 0.45

LWC LWC LWC CLOUD SIZE

center (-6 in) (AVERAGE) H x W (ft)

0.84 0.80 0.84 4.8 x 5.5

1.01 0.92

1.08 0.97

1.76 1.76

1.46 1.46

0.96 4.2x5.5

1.01 4.2x5.3

1.68 4.0x5.2

1.30

0.60 0.57 0.60

0.69 0.67 0.68

0.70 0.72 0.69

1.01 1.01 0.99

0.97 0.97 0.94

2.8x4.5

4.5x4.5

4.3x3.5

4.3x3.5

4.0x3.0

2.5x2.3

0.45 0.37 0.42 4.5 x 2.5

0.50 0.40 0.46 4.3 x 2.5

0.50 0.42 0.46 4.0 x 2.7

0.65 0.55 0.61 3.5 x 2.7

0.55 0.37 0.46 3.0 x 3.0

NASA/TM--2001-210689
(a) Icing tunnel loop before rehabilitation.

_-- OUTLET GUIDE VANES (12)

CONTRACTING \ t /;/

TURNING VANES _t J'/ //

ICING SPRAYS (10 BARS) _ //

/

SPRAY BAR CONTROL ROOM -J CONTROL ROOM

0 lOf_

(b) Icing tunnel loop after rehabilitation.

Figure l.--Illustrations of the NASA Glenn icing research tunnel before and after the recent rehabilitation.

NASA/TM--2001-210689 9
Figure 2.--The icing grid used for cloud uniformity measurement.

NASAJTM--2001-210689 10
60

O,D

"6

i- 40

0

_ 20

_5

Spraybar

number

-- New HX (2000) .... Ideal Location

10

9

9

8

........................................................ i

4

................ _ ............................... 3

3 ........................................................... _ 2

2 ........ _ ...... _ ...... _ _ ....... 1

4-----_ _

0 20 40 60 80 100

Distance from inner wall of test Section, (in.)

Figure 3.--Results from single spray bar test showing where the peak ice accretion occurs

compared to the geometric projection of the spray bar locations into the test section.

60

t---

tO

co

0)

I- 40

o

0

..Q

_ 2o

t-

.o2_

a

--_ew.X" ': / I:: I I/ Ii _/ li

(2000) 44 '. 40 36 32 28 27 23 19 15

4o... t."""".'. ; ",, !: ;; ," :",...,

o

0 20 40 60 80 100

Distance from inner wall of test Section, (in.)

Figure 4.--Results from single columns of spray nozzles showing where the peak ice accretion occurs

compared to a similar test with the previous heat exchanger.

11

American Institute of Aeronautics and Astronautics
-36 -30 -24 -18 -12 -6 0 6 12 18 24 30

Distance from Centerline (in.)

69

63

D

57 i

s

51 t

a

n

45

c

e

39

f

33 r

o

m

27

21

3

36

15

0.50-0.60 •0.60-0.70 ==0.70-0.80 •0.80-0.90 •0.90-1.00 • 1.00-1.10

• 1.10-1.20 • 1.20-1.30 • 1.30-1.40

Figure 5.--LWC uniformity contour plot for the Standard nozzles. Airspeed = 150 knots, MVD = 21 um,

nozzle air pressure = 20 psig. The legend and axis titles apply to all plots in figures 6 through 8.

12

American Institute of Aeronautics and Astronautics
-36 -30 -24 -18 -t2 -6 0 6 12 18 24

69

63

57

51

45

39

33

27

21

15

9

3

30 36

(a) Airspeed = 100 knots

-36 -30 -24 -18 -12 -6 0 6 12 18

(b) Airspeed = 150 knots

69

63

57

51

45

39

33

27

21

15

9

-3

24 30 36

Figure 6.--Mod 1 nozzle LWC uniformity plots for airspeeds of 100, 150, 200 and 250 knots.

MVD=21 urn, nozzle air pressure=20 psig.

13

American Institute of Aeronautics and Astronautics
69

63

57

51

45

39

33

27

21

15

9

-36 -30 -24 -18 -12 -6 0 6 12 18 24 30 36

(c) Airspeed = 200 knots

.3

-36 -30 -24 -18 -12 -6 0 6 12 18 24 30 36

(d) Airspeed = 250 knots

Figure 6.--Concluded.

14

American Institute of Aeronautics and Astronautics

69

63

57

51

45

39

33

27

21

15

9
-36 -30 -24 -18 -12 -6 0 6 12 18 24 30

69

63

57

51

45

39

33

27

21

15

9

3

36

Figure 7.--Mod I nozzle LWC uniformity plot for a nozzle air pressure of 40 psig.

Airspeed = 150 knots, MVD=21 urn.

-36 -30 -24 -18 -12 -6 0 6 12 18 24

69

63

57

51

45

39

33

27

21

15

9

3

30 36

Figure 8.--Mod I nozzle LWC uniformity plot from before the tunnel rehabilitation.

Airspeed = 217 knots, MVD=21 um, air pressure = 20 psig.

15

American Institute of Aeronautics and Astronautics
Figure 9.--Picture of the FSSP droplet sizing instrument mounted in the test section of the IRT.

16

American Institute of Aeronautics and Astronautics
E

<

>_-

I--

CO

Z

W

D

rr

uJ

m

Z

1E+3

1E+2

1E+1

1E+0

1E-1

1E-2

1E-3

1E_

1E-5

1E_

i

I

[]

I

1 10 100 1000

DROPLET DIAMETER, [um]

Figure 10.--Number density drop distribution measured by the FSSP and OAP. MVD = 25 Jam.

100

90

80

A

70

t,.}

J--I 60

IM

_> 50

I,-

'_ 40

_ 30

20

10

IB

0 25 50 75 100 125 150 175 200 225 250

DROPLET DIAMETER (microns)

Figure 11.---Cumulative percent LWC droplet distributions for MVD values of 15, 20 30 and 40 _rn.

These distributions are from measurements of the Mod 1 nozzles.

NASA/TM--2001-210689 17
E

£3

E

=

o

>

_5

I

45

4O

E

::L

. 35

30

25

20

15

10

! ! _ ! I

10 15 20 25 30

I I I ! I ' I I

35 40 45 50 55 60 I

5

0 25 50 75 100 125 150

Water Pressure - Air Pressure, psid

Figure 12.--The droplet size calibration curves for the Standard nozzles plotted as MVD versus AP

for the complete range of air pressures.

50 T

Air Pressure 10

psig

45

40

15

10

5

0 5O

E

=L

35

E

.__ 30

a

E

-= 25

e-

_ 2o

20 25

100 150

Water Pressure - Air Pressure, psid

3O

200 250

Figure 13.--The droplet size calibration curves for the Mod 1 nozzles plotted as MVD versus Ap

for the complete range of air pressures.

NASA/TM--2001-210689 18
................ i i

60 _ ....

I 1 i

40 ' =

I I

!

i i i

30 ! : I /

_-O.0475Rair + 17.421

Ka R2 = 0i7936 , i

2o

lO _ I ' i i

0 10 20 30 40 50 60 70 80

AIR PRESSURE (psig)

Figure 14.--Effect of nozzle air pressure on "K" for the Standard (upper curve) and Mod 1 (lower curve) nozzles.

50

40

= _(V) - 23.72{

20

10

R 2 = 0.951

o i i

0 50 100 150 200 250 300

AIRSPEED (kts)

Figure 15.--Effect of tunnel airspeed on "K" for the Standard (upper curve) and Mod 1 (lower curve) nozzles.

NASA/TM--200 i -210689 19
t_

_J

t_

3.00

2.50

2.00

1.50

1.00

0.50

+10 c

,10%

i

0.00 ; _ _ , ,

0.00 0.50 1.00 1.50 2.00 2.50 3.00

CALCULATED LWC

Figure 16.--A comparison of the LWC measured by the icing blade to the LWC

calculated from the calibration equations.

3.0 , i

i 2.5 i i i

2.0

,

o.o i _--4-----_

15 20 25 30 35 40 45

Median Volume Diameter

50

Figure 17.--The LWC/MVD icing certification criteria from FAA FAR Part 25, Appendix C.

NASA/TM--2001-210689 20
3.0 J

• ,, __ ..... - " - FAAAppendixC j

, . n "., E i i ...... I

' ',._#" " ' ' i " _ =Mod 1 Nozzles

_ 2.5 ........ il * /%" i" • ......., ...... ...... Standard Nozzles J

U 1,5

_ 1.0

a " _ ....... ._.i " i i i i..

- ' " ............ h _ D

-7 0.5

10 15 20 25 30 35 40 45 50

DROPLET SIZE MVD (um)

Figure 18.--Comparison of the LWC/MVD operating envelopes for the IRT to the FAA icing

certification criteria for an airspeed of 100 knots.

3,0

A

¢_ 2.5

v

Z

LU

Z

0

0

LU

h-

<

a

,.J

................... • ,m - - - FAAAppendixC

q

| . _ ..................

. t .................. Mod 1 Nozzl_

|

m .... _, ............... _ --'Standard Noc_.zles

Jill ,_, ..................

' , . , L

2,0 i i : ' ? ? ,'i.i i i ..... ' ' ' ' ' ' ' ..__..----------------.

ip inlim mlira /

.... i ........ ,%, ,p..,,.d," _ ..... I

i i i , i i ? i ? i i...,i,-¢ i i ? i i i i i . ........ I

1"5 i : i i :, i i i.._i i i "-I.I i : i : i i i i i i i I

I

..... m , i - . i i i i i i i ; i ,..i i i i i i i i i i i i i I

t# ../"_',i." • ' i ........... ,, ',,, ........ I

: : : ,,_,,_...,,.--..,.,-,-,,

IF i _-_'_ji.B,,mlq_ " - /

.... i.....----- .

_imm I llmm mim__ . n

0.0

10 15 20 25 30 35 40 45 50

DROPLET SIZE MVD (um)

Figure 19.--Comparison of the LWC/MVD operating envelopes for the IRT to the FAA

icing certification criteria for an airspeed of 300 knots.

21

American Institute of Aeronautics and Astronautics
3

-36 -30 -24 -18 - 12 -6 0 6 12 18 24 30 36

Distance from Centerline (in.)

0.20-0.40 •0.40-0.60 •0.60-0.80 •0.80-1.00

• 1.40-1.60 • 1.60-1.80 • 1.80-2.00

• 1.00-1.20 • 1.20-1.40

69

63

D

57. I

S

51 t

a

n

45

c

e

39

f

33 r

o

m

27

F

21 I

o

15 °

r

Figure 20.--The LWC uniformity contour plot for an MVD of 120/am and an airspeed of 200 knots.

22

American Institute of Aeronautics and Astronautics


Form Approved REPORT DOCUMENTATION PAGE

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this

collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports. 1215 Jefferson

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704o0188), Washington. DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

March 2001 Technical Memorandum

4. TITLE AND SUBTITLE

Icing Cloud Calibration of the NASA Glenn Icing Research Tunnel

6. AUTHOR(S)

Robert F. Ide and John R. Oldenburg

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

John H. Glenn Research Center

Cleveland, Ohio 44135-3191

and

U.S. Army Re,arch Laboratory

Cleveland, Ohio 44135-3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

and

U.S. Army Re,arch Laboratory

Adelphi, Maryland 20783-1145

5. FUNDING NUMBERS

WU-711-21-23-00

1L16221 IA47A

8. PERFORMING ORGANIZATION

REPORT NUMBER

E-12616

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM--2001-210689

ARL-TR-2383

AIAA-2001--0234

11. SUPPLEMENTARY NOTES

Prepared for the 39th Aerospace Sciences Meeting and Exhibit sponsored by the American Institute of Aeronautics and

Astronautics, Reno, Nevada, January 8-11, 2001. Robert E Ide, U.S. Army Research Laboratory, NASA Glenn Research

Center; and John R. Oldenburg, NASA Glenn Research Center. Responsible person, Robert E Ide, organization code

0300, 216--433-3937.

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category: 37 Distribution: Nonstandard

Available electronically at httn://_ltrs._rc.nasa._ov/GLTRS

This publication is available from the NASA Center for AeroSpace Information, 301-621-0390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

The icing research tunnel at the NASA Glenn Research Center underwent a major rehabilitation in 1999, necessitating

recalibration of the icing clouds. This report describes the methods used in the recalibration, including the procedure used to

establish a uniform icing cloud and the use of a standard icing blade technique for measurement of liquid water content. The

instruments and methods used to perform the droplet size calibration are also described. The liquid water content/droplet

size operating envelopes of the icing tunnel are shown for a range of airspeeds and compared to the FAA icing certification

criteria. The capabilities of the IRT to produce large droplet icing clouds is also detailed.

14. SUBJECT TERMS

Aircraft icing; Icing instrumentation; Icing wind tunnel; LWC;

Droplet sizing; Icing tunnel calibration

17. SECURITY C LASSIFICATION

OF REPORT

Unclassified

18. SECURITY CLASSIFICATION

OF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

15. NUMBER OF PAGES

29

16, PRICE CODE

AQ_

20. LIMITATION OF ABSTRACT

NSN 7540-01-280-5500 Standard Form298(Rev. 2-89)

Prescdbed by ANSIStd. Z39-18

298-102
100

90

10

0

0

1 l

I 1 i

/II m

|

100 200 300 400 500 600 700

70 um

i

i --0_ 100 um

i ---A- 120 um

II

+ 175um

I

I + 270 um

I

i i

800 900 1000

DROPLET DIAMETER (microns)

Figure 21 .---Cumulative percent LWC distributions for the large droplet test conditions of the IRT.

NASA/TM--2001-210689 23