Study Of The Mechanism Of Flow And Heat Transfer On Supersonic Transpiration Cooling

Thermal protection for aerospace vehicles has become a great challenge due to thehigh thermal loads experienced in liquid fuel rockets and scramjet chambers.Transpiration cooling is one of the most promising cooling techniques for protecting thesurface from ablation in the high temperature supersonic mainstream. Studies of thetranspiration cooling mechanism with real working conditions are very important for thedevelopment of liquid fuel rockets and super/hypersonic vehicles.Transpiration cooling studies using low velocities mainstream and temperaturescan not directly model the transpiration cooling characteristics for real workingconditions. This study used a supersonic wind tunnel with Mach number3toexperimentally investigate supersonic transpiration cooling. The wall temperatures weremeasured by an infrared camera and a schlieren system to observe the shock wavestructures. The flow and heat transfer mechanisms of sintered porous structures, wovenwire mesh structures and curved sintered porous structures were investigatedexperimentally and numerically. The results show that the velocity gradients near thesurface are significantly reduced by the coolant transpiration, with bronze porous walltemperatures lower than stainless steel wall temperature because of the higher thermalconductivity and that the cooling effectiveness did not change much with themainstream total temperature.A transpiration cooling scheme was developed for struts using a sintered metalporous medium provide thermal protection for struts in scramjet chambers.Transpiration cooling experiments using methane as the coolant with supersonic, hightemperature main flow demonstrated that this strut cooling scheme provides effectivethermal protection. The temperature distribution measured by thermocouples welded tothe bottom of the strut indicated that the system parameters can be optimized tosignificantly improve the cooling.In addition, analytical and numerical methods were used to calculate thetranspiration cooling temperature distribution in the porous media using the LocalThermal Non-Equilibrium model. The analytical model predicted the temperaturedistribution in the porous wall with different coolant entrance boundary conditions. Numerical simulations were used to evaluate the temperature changes caused by thesimplifications in the analytical solutions. Transpiration cooling using a microporousmedia was also numerically studied. The analytical solutions showed that theconvection heat transfer at the entrance should be considered with low Reynoldsnumber flow; otherwise, the solution will underpredict the temperatures. Comparisonsof the numerical results with the analytical solutions indicated that the material thermalproperties and the thermal diffusion term significantly affect the pressure andtemperature distributions in the porous matrix. The transpiration cooling simulations inthe microporous media showed that the wall temperature jump increased thetemperatures in the microporous wall while the velocity slip effect reduced the pressuredrops between the inlet and outlet surfaces.