Study On Heat Transfer And Boundary Layer Flow Of Transpiration Cooling

Aircraft propulsion technology has been undergoing rapid changes and continuous innovation.The improvement of aircraft technical parameters also means the improvement of thermal protection requirements.However,in terms of current technological development trends,cooling technology has become one of the bottlenecks in the future development of aircraft technology.Transpiration cooling is a cooling technology that can further enhance the thermal protection capability of aircraft.In this thesis,the following research work was carried out with transpiration cooling as the research object:For transpiration cooling with coolant channel,this thesis proposes a zerodimensional model based on thermal equilibrium,and analyzes the mathematical relationship between coolant injection ratio,coolant channel flow ratio and cooling efficiency.The zero-dimensional model is presented in the form of a multivariable nonlinear function,and the cooling efficiency is found to be expressed as a continuous smooth monotone bounded surface in the Cartesian coordinate system.The projection of the surface characterizes the effect of coolant injection ratio and coolant channel flow ratio on cooling efficiency.In view of the heat transfer and flow law of transpiration cooling at low speed,this thesis carries out the experimental study on the transpiration cooling of porous plates and porous channels.RANS numerical simulations are used to study the effects of coolant injection,coolant flow organization,and coolant loss on transpiration cooling.The results show a good correlation between coolant injection ratio and cooling efficiency.The injection mode and flow direction of the coolant affect the tangential velocity distribution of the porous wall,resulting in a change in the heat transfer law along the coolant channel.The results also show that there is a coolant consumption increase threshold that does not achieve a positive gain in cooling efficiency.In this thesis,the porous wall channel flow experiment and LES numerical simulation were carried out to study the interference of the coolant injection process on the porous wall boundary layer in the transpiration cooling.The law of flow with porous wall in transpiration cooling and the law of vortex motion in the boundary layer have been studied.It is found that there is periodic vortex motion in the boundary layer of the porous wall,and the vortex is generated with a clear core structure.The low-temperature coolant actively entraps the high-temperature fluid near the wall into the vortex,and the vortex periodically appears,develops and breaks.Aiming at the heat transfer and flow law of transpiration cooling under supersonic conditions,the thesis carries out numerical simulation and experimental research on transpiration cooling under supersonic conditions.A multi-region multi-stage transonic numerical simulation scheme is proposed.The results show that the leading edge of the porous nose cone induces obvious bow shock wave and oblique shock wave in the supersonic flow.The interaction between the shock wave and the boundary layer causes that the parameter distribution in the boundary layer of the porous wall deviates significantly from the wall law under the steady free flow velocity.This thesis proposes a porous cylindrical structure for liquid transpiration cooling.Under the condition of total coolant flow rate of 26 g/s,the average cooling efficiency of the porous cylindrical structure in the inflow environment of Mach number 2 and total temperature 1165 K is not less than 0.85,and the maximum cooling efficiency can reach 0.91.