COMPACT TRANSPIRATION COOLING SYSTEMS - Jhuapl.edu

pirant flow distributions within the porous matrixand then calculates radiation, conduction, andmass flow heating rates between elements. Othersubroutines in the program compute aerodynamicheating rates to surface elements. These rates arecorrected for film-cooling and transpiration blowing when appropriate and are then used to compute new element temperatures at a subsequenttime.The capability of calling subroutines as they arerequired for each individual application providessubstantial generality to the TDTC program andallows it to be used in analyzing a variety oftranspiration cooled systems other than the compact plenum system for which it was orginallywritten.vide experimental data for comparison withanalytical values computed using CTC. Additionalinformation on the test program has been published by Newman. 2The leading edge test model is shown in Fig. 3aand schematically in Fig. 3b. It is made of stainless steel and has a Ih -inch-diameter leading edgeof 5 1;4 -inch span affixed to a 1/2 -inch-thick, hollow flat plate extending 3 3;4 inches aft. A I/s-inchwide porous segment extends along the leadingedge in the manner shown in Fig. 2. The compact plenum has a bore of 0.186 inch and runsalong the centerline of the leading edge.The test model instrumention is also shown inFigs. 3a and 3b. Model surface temperatures weremeasured at the matrix centerline (T?" T 4, T :5 ),Transpiring Model Test ProgramR . W . Newman, Compact Tran spiration Cooling Free-Jet TestResults and Comparison with Theory, APL / JHU TG 1178,Oct. 1972 .2A free-jet test program was developed to pro-r--------- ------------------------. 5 25 (POROUS SEGMENT),.T3T4Ts1/4 DIAMETERTUBING T3,4,SFig. 3-(a) Porous leadingedge test model; (b) Testmodel with temperature andpressure instrumentation.T6,7,S ---"-- T6---- T7-----Ts;-- ----- -- .:::.tc:. ,;:T9:.- ---n:TIO::-":;:-- Tl1 ':I - -::': - .:f -T-, 10,-II oL- .JL. -'L. -'L .IL .1.JPsPsP9P129TIST17 TIST16 -------------------- . . . 9.0 - - .""'1T - THERMOCOupi ESP - STATIC PRESSURE PROBE16U0.0:.; . . . .1-.-/DIMENSIONS ARE IN INCHESAPL T echnical Dige st

NOZZLE - 6.1 INCHES EXIT DIAMETER4.7 INCHES THROAT DIAMETERTA,PA.TBPA , TA,TBHYDROGEN -Fig. 4--Schematic of free-jetsystem.tOXYGENSHIELD SUPPORTPNEUMATICALLY ACTUATEDaft of the centerline at 45 (Tn, T 7 , T s ) and at90 (T!) , T lo, T 11 ). Also measured were temperatures on the inside of the flat plate section (T 1;'and T 1 f; ) and the nitrogen gas temperature at theentrance and exit of the test section (T 1 and T IS).Test model instrumentation included measurements of static pressure inside the compactplenum. Pressure transducer Pc, measured theabsolute static pressure at the entrance of theporous plenum section. Pressure changes alongthe compact plenum axis were measured by threedifferential pressure transducers located betweenstations P5 and PS J Pf) , P l ?, respectively.The nitrogen coolant flow system consisted of asonic flow metering orifice placed upstream of themodel to provide a constant nitrogen flow rate tothe compact plenum test section. Constant nitrogen flow out of the test section was achieved viaa second orifice and a pressure regulator placed atthe exit of the plenum section. Water baths priorto each orifice eliminated time-dependent temperature variations in nitrogen gas entering eachorifice.Before conducting free-jet tests, it was firstnecessary to run several bench tests on the transpiration cooled model and its associated nitrogenflow regulating system. These tests determined themodel porous matrix flow-resistance coefficientsfor each of five axial sections. They also determined the average inner-wall roughness coefficient,and the discharge coefficients of the flow regulating orifices.The free-jet system consists of a hydrogenoxygen vitiated-air heater, baffle, mixing section,and Mach 2 nozzle shown schematically in Fig. 4.May-June 1972A vitiated heater was chosen since it provides thecleanest air of the heaters available. This was important since any particles present in the teststream would impinge on the porous leading edgeand decrease its permeability. However, evenusing the vitiated air heater, the airstream wasnot entirely free of particles.The baffle and mixing sections were placeddownstream of the heater to promote completemixing and burning of the hydrogen-oxygen mixture. This was necessary to give a uniform temperature airstream at the entrance to the nozzle.A Mach 2 nozzle was attached directly to themixing section and the model was supported fromthe nozzle. A movable shield was placed in frontof the test model to reduce model heating andparticle damage during start-up.The free-jet system was instrumented as shownin Fig. 4. The total temperature of the stream wasmeasured by total temperature probes T.t and T B ,located in the nozzle exit plane and additionalprobes (T c, T D , Tr; ) located upstream of thenozzle. A total-pressure probe PI was mounted atthe nozzle exit plane and a static pressure tap(P (' ) was located in the mixing section.Free Jet Test Results-Five runs were madeon the transpiring leading-edge model. Each ofthese was conducted with nearly the same free-jetstream conditions, but with significantly differenttranspirant flow rates. Each test required nearlythree minutes for the model temperatures to cometo equilibrium. More than half of this time theshield was in front of the model while the desiredsteady free-jet stream conditions were being established. Temperature and pressure histories for a17

typical run are presented in Fig. 5. The freestream total temperature (T A) reached a steadystate value of 500 F at 60 seconds after risingabruptly to nearly 600 F during heater start-up.At 90 seconds, when the protective shield wasremoved, the model surface temperature increasedas indicated. At this time, the plenum pressurealso increased slowly owing to the finite time required to increase the gas density in the plenumand its associated transducer lead lines. The unexpected decrease in nitrogen gas exit temperaturefollowing shield removal and temperature increasefollowing free-jet shut down, were also related tothe density change in the associated nitrogenlines.RUN NO.-- - - ---------Min103XMcx X 10301.262.0613.9412.3612345Mt X00.0540.1013.5010.8610301.201.960.441.501.0r - - - - - - - - - - - - - - - - ,0.5 , .",.,. .".1. .,.,,,---t---!. .Io0.20.81.01.21.82.0S-DISTANCE FROM STAGNATION LINE (inches)IMex:II:--TOTAL TEMPERATURE - TA- - NITROGEN TEMPERATURE ATPLENUM EXIT - T 18 PLENUM PRESSURE - Ps MODEL STAGNATION LINE SURFACETEMPERATURE - Ts600 r - - - - - - - - - ".-.,- - .'IIIIIIII. .·. . . . \ . --1r:- - ,." SHIELD/'REMOVALwI I IIII \\,/,/ITg - GAS TEMPERATURE ATENTRANCE TO MODELT t - STREAM TOTALTEMPERATUREMt - TRANSPIRINGNITROGEN FLOW RATEI!Si NITROGEN COOLANT IN Min0 42 00.2 . .---- o.o- .MACH 2STREAMCOMPACT PLENUMPOROUS STAGNATION REGION Wl00IW1 1 IWFig. 6--Experimental normalized surface temperatures.TIME (seconds)Fig. 5-Transient temperature and pressure data forfree-jet run No.2.During testing, the main-air total temperatureand inlet nitrogen gas temperatures varied somewhat from one run to the next. The variationshave been removed by using these temperaturesas reference values as noted on the ordinate ofFig. 6. The normalized surface temperature distributions over the model leading edge presentedin Fig. 6 show Run 1 to have the highest surfacetemperatures at all stations, corresponding to thefact that there was no coolant flow (see Table 1).On the other hand, Runs 4 and 5 had very largeaxial through-flow which provided a large amountof ordinary duct-cooling effect. This is seen bythe response of the nonporous outer surfaces atS 0.2, S 0.4, and S 1.0 in Fig. 6. Theimportance of transpiration cooling becomes clearwhen Runs 4 and 5 are compared. Run 5 had18less total mass flow than Run 4 and yet bettercooling was provided at the stagnation line. Theeffectiveness of transpiration cooling is even morenoticeable when Runs 3 and 4 are compared. Inthe critical stagnation region , Run 3 actually provided better thermal protection with less than 1/ 6the mass flow of Run 4. In summary, the nonporous outer surface temperatures were dependentprimarily on the amount of ordinary duct-coolingeffect and the porous stagnation surface temperatures were strongly dependent on the transpiration mass flow rate. A comparison of Runs 4 and5 shows no significant film-cooling effect.Comparison of Computed andExperimental ValuesThe primary purpose of the free-j et test program was to provide data for use in evaluatingthe eTC computer program. Therefore, experimental and analytical results in the following fourareas were compared:APL T echnical Digest

TABLE 1TRANSPIRATION MODEL TEST CONDITIONS, EXPERIMENTAL RES ULTS, AND COMPUTED RESULTSNitrogen Mass Flow Conditions(fbi s X 10- 3 )RunI2345PlenumInlet FlowPlenumExit FlowFlow .201.960.441.50510487527512517III1. Surface temperature (Ta through T 11 , Fig.3b) .2. Nitrogen gas temperature rise along plenumaxis (T p .: , Fig. 3b).3. Static pressure in compact plenum (P ;"Fig. 3b).4. Static pressure distribution along compactplenum (Pc" P , Pf) , P l ' Fig. 3b).Analytical Model-The analytical model usedin the eTC computer program is shown in Fig. 7.Only half the test model was analyzed since flowconditions are symmetric for both the top andbottom halves. The analytical model is divided NITROGENFLOWLEAVINGCOMPACTPLENUMEXTERNAL AIR-FLOW SECTION A-AFig. 7-Analytical model of transpiring leading edgefree-jet test model.May -June 1972Test-Jet xperimen tallComputedGas Temp.at PlenumOutlet(OF)Experimen tallComputed78/ 78197.4/ 208269.2 / 274139.2/ 139.3234.6/ 237452 / 346/ 273362/ 258113/ 129126/ 138into six axial sections, four radial sections, andsix sections in the external flow direction. Thenitrogen flow rate entering and leaving the compact plenum sections are specified from measuredexperimental values. The eTC program uses thesevalues and the matrix flow-resistance coefficientsto compute the plenum pressure required to forcethe given transpirant mass flow through the porous matrix. In this calculation the nitrogen flowthrough the porous matrix is assumed to be unidirectional with no circumferential cross-flowwithin the matrix.Aerodynamic heating rates to the porous surface elements in the stagnation region were computed in eTC using the Sibulkin equation 3 andthe experimentally measured stream total-temperature and total-pressure. Heat transfer coefficients for solid surface elements adjacent to theporous matrix employed the stagnation heatingequation with a cos () correction factor. Heatingrates to the remaining solid surface elements werecomputed from flat plate theory and were reduced by radiation to room temperature assuming a surface emissivity of 0.9. eTC correctedeach local heating rate for transpiration blowingor film cooling according to correction techniquesthat have been presented.4.5Correlation of Surface Temperatures-Of primary importance in checking the computer program is the correlation of computed model sur3 M. Sibulkin, "Heat Transfer Near the Forward StagnationPoint of a Body of Revolution," 1. Aero. Sci. 19, Aug. 1952,570-571.-! E. R. G. Eckert and R . M. Drake, Jr., Ana/)Isis of Heat andMass Transfer, McGraw-Hill, New York, 1972." R. J. Goldstein, G. Shavit, and T. S. Chen, " Film CoolingEffectiveness with Injection through a Porous Section," J. HeatTransfer 87, Aug . 1965, 353-361.19

1.0 0.9 1l:I;'I(-o-i 0.8a 0.7(-o 0.6ozT. - GAS TEMPERATURE AT ENTRANCE TO MODELTt - STREAM TOTAL TEMPERATURES0.2 ·42.0I- 0 . 0 - 'MACH 2STREAMFig. 8-Summary of computed surface temperaturesat the center.face temperatures with experiment. A summaryof computed values for all five runs is presentedin Fig. 8. The results show a striking similaritywith the plot of experimental values (Fig. 6).The computed results follow the same generalcontours of the experimental data.However, the computed values are somewhatlower than measured especially at the stagnationline where the experimental temperatures lie approximately half way between the analyticallydetermined temperatures and the temperatures forzero transpiration cooling.The relatively large temperature difference atthe stagnation line is likely due to the effect of freestream turbulence in the nozzle. Experimental datapreviously presented 6 indicate that for a cylinder insubsonic crossflow the stagnation line heat transfer coefficient is nearly doubled at turbulencelevels as low as 2.3 % . This increase in stagnationline heating could account for the differences inFigs. 6 and 8.Correlation of Nitrogen Temperature RiseAlong Plenum and Correlation of Plenum StaticPressure- Measured and computed steady-statevalues of nitrogen plenum gas pressure (P 5) andtemperature at plenum outlet (T I s) are presentedfj J . Kestin , P. F . Maeder, a ndH. H. Sogin, " The Influence ofTurbulence on the Transfer of Heat to Cylinders Near the Stagnation Point ," Z. Ange w . Math . u Phys. (ZAMP) 12, 1961 ,115- 13 1.20in Table 1. The pressures computed from theCTC program were all in general agreement withexperimental values, indicating that this portionof the computer program was performing satisfactorily. In contrast to the pressure results, experim'ental and analytical results for nitrogen gastemperature at the plenum outlet were not in asgood agreement. In Runs 2 and 3 (Table 1)measured exit gas temperatures were significantlyhigher than calculated values, and in Runs 4 and5 they were lower. It is possible that the combinedeffect of inlet temperature prediction and thermalconduction of the thermocouple may be responsible for the lack of agreement between measuredand computed coolant exit temperature.Two-Dimensional Crossftow Results- An analysis of the central section of the model wasundertaken using the TDTC computer program.The analytical model is presented in Fig. 9 alongwith the results. In the analysis, temperatures ofthe solid elements and the total transpirant flowrate were held constant at values previously predetermined in the CTC program. Aerodynamicheating rates at the outer surface were adjustedfor local blowing. The steady-state results indicatep 11 SOO, 11 760, 11 920, 6.03 S.82 S.69M. x lOSt t t4160F 414 F 413 FELEMENTr ;1 EL T.L. l , · :": (jl· '423 F //// t;:! f 11 :':ri " M ' : r' :;" :'"4200 F//./ --t0T-"{r- '.:.: r ·}·:;POROUSMATRIX4 12 F P Iblft2M IbIst ' 376 F1S.93T S.87M. x lOS S.7Sp 20644Fig. 9-Temperature and mass flow in porous matrixas computed from two-dimensional transpiration cooling program (TOTC).A PL T echnical D ige st

that at the outer surface the transpirant flow rate increases away from the stagnation line and thatthere is very little temperature gradient at theouter surface of the porous matrix. This indicatesthat two-dimensional internal crossflow of thecoolant had relatively little influence on the measured surface temperature.SummaryA computer program has been written to predict temperature, pressure, and mass flow in acompact transpiration cooling system. It is a complex program including: conduction, radiation,aerodynamic heating, material properties as functions of temperature, friction losses, conduction tothe plenum gas, suction effects, blowing effects,and transpiration cooling.To verify results obtained from this program, acompletely instrumented compact transpirationcooled leading-edge model was constructed. Thedata from these tests were compared with analytical values and showed good agreement for absolute pressure in the compact plenum. Measuredand computed surface temperatures had the samegeneral trends and were in good agreement everyplace except in the stagnation region, where itwas felt that free-stream turbulence may havecaused experimental temperatures to be higherthan predicted.A second computer program has been writtento predict three-dimensional temperature, .pressure, and mass flow in a porous matrix of general geometry. The program accounts for threedimensional mass flow of transpirant within amatrix of spatially varying porosity. It is of general form and can be used in other transpirationcooling applications besides the compact plenumapplication.AcknowledgmentThis work was carried out under sponsorshipof the Naval Air Systems Command, specifically,AIR-320B, Lt. Cdr. F. Cundari. Thanks are extended to L. B. Weckesser for his continuedguidance throughout this program, and to J. L.Rice for his contribution in carrying out the freejet tests.HONORS AND AWARDSR . E. Gibson, Director Emeritusof the Applied Physics Laboratoryand Professor of Biochemical Engineering at The Johns Hopkins University School of Medicine, wasawarded the honorary degree ofDoctor of Medicine by The JohnsHopkins University on May 26,1972.A. KossiakofJ, Director of the Applied Physics Laboratory, has beennamed a trustee of the ChesapeakeResearch Consortium. This is an association of academic institutionsconsisting of The Johns HopkinsUniversity, the University of Maryland, the Virginia Institute of Marine Science, and the SmithsonianInstitution. Chartered in January1972, its mission is "to conduct anintegrated and collaborative researchprogram which will contribute tobetter management of the Chesapeake Bay."May -June 1972The APL Technical Digest won aCertificate of Achievement in theCorporate Research Journal categoryat the Third International Publications Competition sponsored by theSociety for Technical Communications. Accepting the award duringthe Society's Nineteenth Annual Conference, held May 10-13, 1972, atthe Statler Hilton Hotel in Boston,were the Digest's Managing EditorP. E. Clark and Staff Artist J. H.Hartle. The winning entry (J anuaryFebruary 1970 issue) was the sameone that won the Award of Distinction last year in local competition ofthe Washington area chapter of theSociety.In a recent contest held by theWashington, D.C. Chapter of theSociety for Technical Communications, APL publications won anaward in each of the five categories.In addition, a special award wasgiven APL in recognition of its highperformance as a multiple winnerfor two consecutive years. Theawards were presented at a dinneron June 23, 1972.An Award of Excellence was received in the Technical Reports category for Heat-EngineIMechanicalEnergy-Stor

transpiration cooling system under study and so as to thermally connect the cooling system to the structural network. CTC input flight history is May - June 1972 user-specified in terms of (a) local flow conditions versus Mach number, (b) Mach number and alti tude versus time, and (c) atmospheric properties .