Research On The Transpiration Cooling In Supersonic And High Temperature Flow

With the development of aerospace technology, thermal protection has become a great challenge for componentssuffered high thermal loads in rockets and scramjet engines. Transpiration cooling technology has the advantages of high cooling efficiency and low coolant consumption. Studies on transpiration cooling heat transfer and flow mechanisms in supersonic and high temperature flow becomes vital important.The literature on supersonic transpiration cooling mainly focused on transpiration cooling using flat porous plate, while the existence of shock waves in the supersonic flow field was inevitable and the impact of the shock wave on supersonic transpiration cooling was still unclear. In this paper, the mechanism of shock wave effect on the supersonic transpiration cooling in porous flat plate was investigated experimentally and numerically.The experimental study was conducted in aMa=2.8supersonic wind tunnel.The temperature of porous surface was measured with a thermal infrared imager and the flow field was observed with a schlieren system. The results showed that oblique shock wave would increasethe surface recovery temperaure and local static pressure, resulted as decreased coolant massflow and cooling efficiency.The influences of shock waveintensity, porous matrix properties and coolant conditionson cooling performancewere summarized.A transpiration-cooled strut for scramjet engine was tested in the T0=1800 K, Ma=2.5 mainstream withmethane and RP3 kerosene as coolant andthe sweepback strut structure showed better cooling performance. A 3D CFD mdoel was established to analyze the influence of coolant inlet conditions, porous matrixproperties andstrut wedge angle on the cooling effect and fuel residence time. The increase of coolant blowing ratio was always beneficial for improving the fuel residence time whileit was restricted by the structure strength. Transpiration-cooled strut obtained best cooling performance when the wedge angle was 30 degrees.The heat transfer process of transpiration cooling was analyzed with a simplified thermal resistance analysis model with the effect of thermal nonequilibrium within porous zone considered. The temperature distributions of the porous and mainstream were derived with coupled boundary conditions. Theheat flux bifurcation mechanism on the fluid/porous interfacewas analysed.Anexperimental system was established for high temperature transpiration cooling study and the mainstream temperature could be as high as 1000 K.At the first, air was chosen as the cooling medium and the transpiration cooling characteristics with bronze sintered porous plate. The influence of mainstream condition, cooling flow injection rate and particle diameter on transpirationcooling effect was investigated.The temperature difference between fluid phase and solid phasewas measured for the assessment of the thermal non-equilibrium effect. Then, pure water was used as the cooling medium and the transpirationcooling characteristicswith coolant phase change was investigated. Results showed that transpiration cooling with coolant phase change could get higheraverged cooling efficiency, but local overheating areas emeraged in the upstream plate, which would decrease the cooling performance.