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AIAA 98-0097Development of the Cox Icing ResearchFacilityK. Al-Khalil, L. Salamon, Cox & Company, Inc.New York, NY 10014G. Tenison, Tenison Engineering Inc.Brecksville, OH 44141
36th Aerospace SciencesMeeting & Exhibit
January 12-15, 1998 / Reno, NV
1American Institute of Aeronautics and Astronautics
AIAA 98-0097
*Engineering Scientist & Manager, Member AIAA†Plant Manager‡Engineering Consultant, Member AIAA
Copyright © 1997 by the American Institute of Aeronauticsand Astronautics, Inc. All rights reserved.
DEVELOPMENT OF THE COX ICING RESEARCH FACILITY
Kamel Al-Khalil*, Laszlo Salamon†Cox & Company, Inc.New York, NY 10014
Gary Tenison‡
Tenison Engineering Inc.Brecksville, OH 44141
ABSTRACT
The LeClerc Icing Research Laboratory was designed and constructed at Cox & Company in downtownNew York City (Manhattan). The facility was engineered to meet a number of design criteria in addition tobeing environmentally non-intrusive to the surroundings. It consists of a closed-loop refrigerated wind tunnelwith the capability to simulate a cloud of supercooled water droplets as specified in the FAR’s Part 25-C. Twotest sections are provided with an airspeed up to 220 mph in the main test section and 120 mph in thesecondary one. Provision for testing engine inlet nacelles is provided with a scavenge system that is capableof simulating engine core air flows of up to 15 lb/sec. The tunnel air temperature can be controlled down to–22 �F at the maximum heat load conditions.
I. Introduction
EXTENSIVE testing, in-flight and ground, isnormally required in the design and evaluation of
ice protection systems. The cost involved can besomewhat prohibitive. Flight testing requiressearching for natural icing conditions or flying behindan icing tanker which is time consuming and verycostly. Furthermore, natural icing conditions tend tobe short and uncontrollable. The cost anddevelopment period involved can be reduced bytesting in ground facilities that can reliably producecontrolled icing environments. Additionally,experimental data (ice shapes and ice protectionsystem performance) in conjunction with icingsimulation computer codes may be utilized in thecertification process to shorten the required flighttesting matrix, once approved by the FAA.
The LeClerc Icing Research Laboratory (LIRL) wasconstructed in Cox’s plant, in a business district ofdowntown New York City. It is completely enclosed,engineered and constructed to be quiet and non-intrusive to the surroundings. It was designed tomeet the company’s need for its own productdevelopment, to support the certification process ofthese products, and to provide industry with anefficient and cost effective tool to promote the safety
of flight worldwide.
II. Facility Design and Description
Several issues were involved in the decision processto build the facility. First was the selection of theconstruction site. Due to the noise level expectedfrom the operation of all subsystems, initialconsideration was given to build the facility off-site(not in Manhattan) of the company’s plant. However,the inconvenience and the additional cost involved tooperate a totally separate facility overruled thatconsideration. It was decided to build the facilitywithin the existing company space. In order to doso, the following criteria had to be met:
� All tunnel components must fit through a 3rd floorwindow of our downtown Manhattan commercialoffice building
� Power must not exceed 800 kW� A minimum of 200 mph airspeed in the main test
section� The air temperature must be controllable from
–22 �F to 32 �F� Noise levels had to be non-intrusive to offices
within the building as well as within the Coxfacility (3 adjacent floors) outside the icingresearch lab area.
� The largest possible test section that meets theabove requirements and constraints in additionto the space assigned to the laboratory.
There were three main challenges: (1) noise issueswithin and surrounding the building; (2) size of thetunnel components and access to the building; and(3) power supply to the building in New York City islimited to 3-phase, 208 volts. The following sections
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discuss the design features of the major sub-systems.
II.1 Structural Design and Acoustics
The LeClerc Icing Research Laboratory is an indoorclosed-loop refrigerated tunnel measuringapproximately 72 ft x 44 ft, in plan view. Figure 1 isan illustration of the tunnel layout. Its basic structureconsists of 0.165 inch thick steel walls withreinforcing ribs. The rib size and location dependson the particular tunnel section and the naturalfrequency of the panel to be reinforced. The totaltunnel structure weighs about 80,000 lbs.
The first challenge to be resolved was the noise andvibration issue. Cox’s facility is located in one ofthree buildings in New York City constructed tohandle an average floor loading of 250 lb/ft2. Whileextremely robust, its 8.5 inch thick solid concretefloors permit vibration and noise to be easilytransmitted to other floors within the 12-storybuilding. Consequently, all components with movingparts have been mounted on floating concreteplatforms which were isolated from the buildingstructure using Super Waffle pads and appropriatelydesigned coil springs. The entire tunnel structureand non-moving parts were isolated from thebuilding structure using concrete platforms andwaffle pads. Moreover, the main axial fan and thescavenge system centrifugal blower were designedwith efficient acoustic silencers on their inlets andoutlets.
The tunnel walls were covered with insulationmaterial for two reasons: (1) minimize the heat loadon the refrigeration system, and (2) reduce thetransmission of “white” noise from inside the tunnelloop to the laboratory surroundings. The insulationconsisted of a combination of closed-cell foam, fiberglass, and air gaps. The overall acoustic treatmentwas so effective that no noise is heard in adjacentfloors or offices nearby the laboratory area. Also,normal conversation is possible within the lab area.
II.2 Test Sections
The tunnel is designed to support testing of liftingsurfaces, engine inlets, and large subsystems suchas aircraft potable water systems and componentsthat do not require a high airspeed environment. Itis a closed-loop system and features two test areaswith the following capabilities:
� A high speed main test area (Test Section 1)� A low speed test area with larger cross-section
(Test Section 2).Additionally, an adjacent large cold chamber isprovided to support full scale testing and
development of systems at low temperature and verylow airspeeds.
The bellmouth between the spray bars (see Fig. 1)and Test Section 1 provides a contraction ratio of9:1. Test section 1 shown in Figure 2 is the maintest area for high speed simulation and angle ofattack variation. It has the following properties:
� Dimensions: 28" wide, 46" high, 6.5' long with 6"fillets that extend from the bellmouth inlet downto the end of Test Section 2.
� Maximum speed: 220 mph.� Rotating side mounts to vary the angle of attack
of airfoil sections.� 4 heated viewing windows (sides at 28" x 22",
top and bottom at 19" x 13").
Left and right side mounts are provided withsynchronized gearing mechanism driven by a singlestepper motor. A Baldor SmartMotor™ with aprogrammable keypad is used to rotate the sidemounts at variable speeds a full 360º.
A diffuser section, 18.75 ft long, following TestSection 1 has a 5º total included expansion angle.This expansion is fairly modest allowing for largermodels in Test Section 1 and a reasonably good flowqualities and uniform icing cloud in Test Section 2.This secondary test area is provided for testing largemodels at lower speeds where a convenient variationof the angle of attack is not required. This sectionhas the following properties:
� Dimensions: 48" wide, 48" high, 5' long with 6"fillets.
� Maximum Speed: 120 mph.� 4 Heated Viewing Windows (sides at 28" x 22",
top and bottom at 19" x 13").
Both test sections are provided with slots for ventingto the ambient air and for setting the referenceambient pressure in either test section. The largeheated windows in the main and secondary testsections are provided for direct clear viewing, videorecording, and still photography of the test article.Lighting is provided by 6 halogen lights in the filletsof each test section. Lights are rated at 500 Wattseach with individual switches for better illuminationcontrol.
II.3 Main Drive
An axial flow fan provides air speeds up to 220 mphin the main test section and is completely containedwithin inlet and outlet silencers for noise control.Additionally, acoustic center-bodies are installed onboth sides of the fan. The drive motor is rated at 200
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hp 3-phase 208 volts A/C running at constant RPM.The fan consists of 16 variable pitch blades at 72"diameter. Airspeed is controlled by an externalpneumatic actuator that sets the appropriate bladetip angle up to 18.5 degrees. Settings areestablished in a closed-loop using airspeed feedbackand an analog signal output from a PID controller.With little model blockage, up to 160,000 scfm airflow can be attained at the maximum blade settings.
II.4 Scavenge System for Engine Inlets
A realistic simulation of the icing process of anengine inlet nacelle requires a good representationof the flowfield, and, consequently, of the stagnationline. The latter affects the locations wheresupercooled water droplets impinge on the surface.In addition, the variation of air flow in and around theinlet is largely dependent on the the flight envelope,for example, during take-off (full power) andapproach (slightly above idle speed).
The tunnel is equipped with an independentscavenging system to simulate the engine inletflowrate. This system, shown in Figure 3, consists ofair ducts just downstream of each test section (eitheror both can be blocked) where air is ingested andthen ducted back into the tunnel loop at the seconddiffuser. This air flow is provided by a centrifugal fandriven by a 75 hp A/C motor. A Variable FrequencyDrive (VFD) is provided for engine flowrate variation.The motor/fan assembly is capable of simulatinginlet air flows up to 15 lb/sec.
Measurement of the flowrate is accomplished usinga venturi. The flowmeter has an inlet diameter of 20inches, throat diameter of 8.13 inches, and a totallength of 110 inches. Two pressure transducers areused to measure the static and differential pressuresin the venturi to compute the flowrate and provideclosed-loop control of the inlet air flow.
II.5 Refrigeration System
The refrigeration system was designed to meet thetunnel cooling requirements. The system, shown inFigure 4, includes a user-friendly microprocessorcontrolled compressor from MYCOM. This unitconsists of a single stage rotary screw compressordriven by a 250 hp motor. The system was designedto provide a cooling capacity of 80 tons at –22 �F airtemperature leaving the evaporator coils. Thecompressor and condenser units are isolated in afully enclosed room. Waste heat is exhausted toCox’s water cooling tower on the roof of the building.
The refrigerant fluid used is R-22. Two identicalevaporators with a total face area of about 141 ft2
are located between Corner 3 and Corner 4 in the
tunnel. This arrangement was selected based onthe maximum space available between the ceilingand the floor, and between building structuralcolumns. Air temperature control is achieved with aPID controller that communicates with thecompressor unit’s microprocessor.
Due to the heat generated by the compressor motorin the enclosed room, cooling was provided by directexchange with outdoor air. Special ducts equippedwith acoustic silencers were required in order tomeet city codes on noise transmission to nearbyresidences.
II.6 Spray System
A spray system was designed to support testing overthe largest possible range of Liquid Water Content(LWC) and Mean Volume droplet Diameters (MVD)as specified by the FAA in Appendix C of FAR-25.Most of the spray system support components,including the water pump, are isolated in anenclosed room, adjacent to the spray bars, for noisecontrol. The spray system relies on compressed airand water to generate a cloud in the tunnel. Thesesubsystems are described in the followingparagraphs.
II.6.1 Spray Bars
Cloud formation is achieved by atomizing liquidwater in nozzles distributed on six horizontal spraybars. Figure 5 illustrates a downstream view of thespray bars. Each spray bar consists of twoconcentric tubes, the outer one for air supply and theinner for water supply. These bars were obtainedfrom the NASA Lewis Icing Research Tunnel (IRT)during the major upgrade to their individuallycontrolled nozzle system in early 1997. Somemodifications were required to accommodate themto the tunnel due to size differences and controlrequirements. Each spray bar can hold as many as17 nozzles at 6" spacing. However, cloud uniformityand normal LWC range require only three or fournozzles per bar, for a total of 18 to 24 nozzles.Location of these nozzles is being determinedthrough cloud uniformity calibration. This effort is inprogress.
II.6.2 Water Supply
The water system consists of the following:
� Three water filters (5 microns).� A de-ionizing system with one activated carbon
tank followed by two mixed bed tanks. Thiscombination yields a water resistance as high as18 Mohm-cm. A meter indicates the actualresistance and an alarm light provides an
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indication of when de-ionizing tank replacementis required.
� A 100 gal water storage tank with heater.� A 5 hp water pump provides more than 4 gpm at
360 psig.� Two high accuracy 0-400 psig pressure
transducers for control feedback.� Two pneumatically actuated control valves.
II.6.3 Air Supply
The compressed air supply consists of the following:
� Water cooled 60 hp air compressor with a totalcapacity of 300 scfm at 100 psig. Additional airis available through other pre-existing companycompressors.
� A 240 gal receiving tank.� Air dryer/chiller.� A 30 kW air heater.� One 0-100 psig high accuracy pressure
transducer for control feedback.� A pneumatically actuated control valve.
II.6.4 Atomizing Nozzles
Air assisted atomizing nozzles are used to create thewater droplets. These are of the NASA Lewis IRTdesign, namely the MOD-1 and Standard (STD)nozzles. The difference between the two is that thelatter yield higher water flow rates for the high LWCcases to be simulated.
The supply air pressure primarily controls the size ofatomized water droplets. The water flowrate througheach nozzle is determined by the difference betweenthe water and the air supply pressures. This is givenby the following equation:
Cm
P Pf
water air
=−
where,Cf = nozzle flow coefficientm = water mass flowrate, gal/min P = supply pressure, psig
The flow coefficient is almost a constant for therange of normal pressures. In order to extend therange of LWC while maintaining a high level ofcontrollability and cloud uniformity, Cox produced avariation of the NASA nozzles designated MODCnozzles. With these three sets of nozzles, the LWCrange from 0.25 to 3.0 g/m3 is covered for morethan 85% of either test section. The flow coefficientof some of these nozzles is shown in Table 1. Oncethe entire set of nozzles is calibrated, the bestselection will be made for use in the tunnel. Threepercent or less nozzle flow coefficient deviation from
the nominal value is considered acceptable.
Table 1: Typical Measured Flow Coefficientsof a Random Number of Nozzles
Nozzle ID FlowCoefficient
% Deviationfrom average
STD-35 0.01290 -0.70STD-36 0.01340 3.20STD-37 0.01310 0.80STD-39 0.01340 3.22STD-40 0.01310 0.80STD-45 0.01330 2.40MOD-400 0.00482 1.69MOD-411 0.00476 0.42MOD-414 0.00465 -1.90MOD-429 0.00473 -0.21MOD-441 0.00476 0.42MOD-520 0.00467 -1.48MODC-1 0.00327 -1.21MODC-3 0.00332 0.30MODC-4 0.00333 0.60MODC-5 0.00333 0.60MODC-6 0.00333 0.60MODC-7 0.00325 -1.81MODC-8 0.00326 -1.51MODC-10 0.00326 -1.51
II.7 Instrumentation and Control System
Control of all tunnel subsystems is achieved by asingle operator from the Master Control Consoleshown in Figure 6. The console houses a personalcomputer (PC) which includes a high speed analogand digital I/O card that communicates with six dataacquisition and control signal conditioners.
Direct control is achieved by 10 individual PIDcontrollers that communicate to the PC via RS-485multi-drop serial communication modules. This built-in redundancy permits control through the stand-alone PID controllers or through software by serialcommunication between the PC and the individualcontrollers. Process and control values arecontinuously monitored by the computer and writtento data files for record keeping and future reference.
III. Present Activities
Preliminary flow calibration was performed to assess
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the air flow quality and uniformity in the main testsection. A 16-channel digital pressure scanner wasused for that purpose. Typical results are shown inFigure 7 where the average airspeed was226.7 mph. The maximum deviation from theaverage was 0.65% near the wall.
Temperature uniformity in the test section is directlyrelated to uniform cooling of the air by therefrigeration evaporator coils. To investigate thismatter, eight evenly distributed type-Tthermocouples were installed, four on the upper coilsand four on the lower one, one foot downstream ofthe coils. The resulting measurements are given inTable 2. This indicates a very uniform airtemperature distribution within the sensors’accuracy. Moreover, the additional mixing throughcorner 4 and the contraction further improves thatuniformity.
Table 2: Temperature Uniformity DataDownstream of Cooling Coils (ºF)
-22.1 -21.8 -22.5 -22.7
-20.3 -20.9 -21.7 -22.0
Cloud uniformity studies are still in progress. A gridof about 5 inch spacing was built and installed TestSection 1. Atomized water was released fromindividual rows and columns of nozzles to map theirlocation on the grid in the test section as describedin Reference [1] for the NASA IRT calibration.Analysis of the results will be used to predict thelocation and number of individual nozzles on thespray bars that yield the most uniform cloud in thetest section. Figure 8 is an example illustrationshowing the ice accretion on the grid resulting froma straight column of six nozzles installed near themiddle of the spray bars. This data can be used torelocate some of the nozzles in order to obtain aneven vertical ice accretion within the NASAacceptable limits of 20% overall uniformity [1]. Thegrid was also installed in Test Section 2 where clouduniformity is even better due to the additional mixingin Diffuser 1.
In an effort to accelerate current productdevelopment schedules, testing of ice protection andice detection systems by Cox and its partners hasalready been initiated. Until actual calibration of thecloud droplet distribution is completed, pre-existingNASA IRT calibration data are being used in theLIRL. It is expected that slightly higher air pressuresare required for the same MDV. This is related tothe shorter distance between the spray bars and themodel in test at LIRL, and subsequently lessevaporation from the droplets. Figure 9 illustrates a
section of a horizontal stabilizer with a hybrid iceprotection system (thermal & low power electro-expulsive) being tested [2].
IV. Future Activities
The following is a list of future activities:
� Perform MVD calibration for MOD-1, STD, andCox MODC nozzles by NASA Lewis engineers.
� Perform a thorough aerodynamic calibration thatincludes flow angularity studies using a 5-holeprobe, and measure the turbulence intensity withand without spray air using hot wireanemometers.
� Complete LWC calibration and documentation.� Conduct ice accretion on standard geometries
including a NACA0012 airfoil and a cylinder tocompare results with the NASA Lewis IRT.
� Experiment with other types of nozzles toexplore the possibility of improving on thenormally accepted 20% cloud uniformity.
� Investigate methods to simulate mixed icing andsnow environments as required by the JAR.
V. Concluding Remarks
The LeClerc Icing Research Laboratory wasdesigned and constructed at Cox & Company facilityin downtown New York City. It consists of a largestatic cold chamber and a closed-loop refrigeratedwind tunnel to simulate environmental icingconditions in two test sections. Airspeeds as high as220 mph can be attained in the main test section attemperatures as low as –22 �F. A scavenge systemis included to simulate engine inlet air flow and allowan accurate representation of the flowfield in andaround the inlet nacelle.
Preliminary aerodynamic calibration, cloud andtemperature uniformity studies have been verypromising. Further calibration will include dropletsize.
The facility will be used mainly for development ofCox ice protection and detection products, and toprovide industry with an efficient and cost effectivetool for systems testing under simulated icingenvironments.
Acknowledgments
The support provided by the technical andoperations members of the IRT and the IcingTechnology Branch at the NASA Lewis ResearchCenter throughout the project is well appreciated andrecognized.
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References
1Ide, Robert, “Liquid Water Content and DropletSize Calibration of the NASA Lewis Icing ResearchTunnel,” AIAA 28th Aerospace Sciences Meeting,Jan 90, AIAA Paper 90-0669, NASA TM-89-C-014
2Al-Khalil, K., Ferguson, T., and Phillips, D., “AHybrid Anti-icing Ice Protection System,” AIAA 35th
Aerospace Sciences Meeting, Reno, NV, Jan. 6-10,1997, AIAA Paper 97-0302.
Figure 1: Layout of The LeClerc Icing Research Laboratory
Figure 2: Main Test Section
Figure 3: Engine Inlets Scavenging System
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223
224
225
226
227
228
-13.
0
-10.
0
-7.0
-3.5 1.0
5.5
8.5
11.5
Distance from Centerline (in)
Velo
city
(mph
)
Figure 4: Refrigeration Compressor System
Figure 5: Downstream View of the Spray Bars
Figure 6: Master Control Console
Figure 7: Typical Velocity Distribution in the MainTest Section
Figure 8: Cloud Uniformity Calibration Grid (onecolumn of nozzles in this case)
Figure 9: An Ice Protected Horizontal Stabilizerunder Testing
