Numerical Study On Heat And Drag Reduction Of Transpiration With Chemical Nonequilibrium Flow Past A Blunt Body

In the future,hypersonic vehicles will fly faster and suffer more severe aerodynamic heat,which will exceed the temperature tolerance limit of all passive thermal protection material systems.How to meet the shape maintaining and drag reduction requirements of near space hypersonic vehicles is the most urgent task.Transpiration technology emerged for drag and heat-transfer reduction.However,traditional simulation does not consider the real complexities in the working process of the transpiration cooling system,and lacks the aerodynamic/thermal model and analysis software with the coupling of the"real gas effect",the the wall catalytic and the transpiration.On the basis of aerodynamic thermodynamics,computational fluid dynamics,physical chemistry and other disciplines,the numerical study on heat and drag reduction of transpiration with chemical nonequilibrium flow past a blunt body is carried out in this paper.The main work and production of the paper are as follows:1.Two-dimensional axisymmetric chemical nonequilibrium flow governing equations are established based on mass conservation equation,momentum conservation equation,energy conservation equation,component diffusion equation and gas state equation.Considering three air species models,namely the 5-species model（N₂、O₂、N、NO and O）,the 7-species model（N₂、O₂、N、NO、O、NO⁺and e^-）and the 11-species model(N₂、O₂、N、NO、O、NO⁺、e^-、N₂⁺、N⁺、O₂⁺and O⁺).The governing equations were discretized by the finite volume method,and the inviscid and viscous fluxes were further discretized by the AUSMPW+scheme and the second-order central difference,respectively.The iterative solution was realized by the implicit time advance method of LU-SGS.It provides a research tool for the comparative analysis of component models and wall catalytic effects in hypersonic flow.In addition,taking the typical configuration of"ELECTRE"and its flight test conditions as an example,the influence of wall catalysis on aerodynamic heat of the 5-species model in hypersonic chemically non-equilibrium laminar flow is studied.The results show that:wall catalysis increases the recombination rate of dissociated atoms at the wall,the chemical heat flux released by the recombination reaction is the main cause of the wall catalytic effect,and the physical heat flux increment caused by the recombination reaction is the secondary cause.2.By using the developed two-dimensional numerical simulation program of axisymmetric chemical non-equilibrium laminar flow,the aerodynamic heat of5-species dissociation model,7-species ionization model and 11-species ionization model in chemical nonequilibrium flow are calculated and compared.The results show that:there is no difference in the wall heat flux of the three models under the condition of non catalytic wall.Under the condition of complete catalytic wall,with the increase of Mach number from 12 to 23,the difference of heat flux on the wall of the three models becomes bigger and bigger,and the difference of heat flux at the height of 50km is greater than that at the height of 40 km at the same Mach number.In the same case,the 7-species model has the largest heat flux and the 5-species model is the smallest.The difference of heat flux is mainly caused by the competition mechanism of dissociation and ionization and the wall catalytic effect.3.Based on the two-dimensional axisymmetric 11-species chemical nonequilibrium laminar flow model,a two-dimensional axisymmetric 11-species chemical nonequilibrium turbulent flow model with air as the transpiration medium is established by introducing the mass injection wall and the Menter SST turbulence model.A numerical simulation program for this model is developed,and the heat and drag reduction on a smooth hemisphere in hypersonic flow are calculated and analyzed.The results show that:on the smooth hemispherical body,the injection air pushes the high-temperature incoming flow away from the wall,increases the shock wave breakaway distance,and effectively reduces the friction resistance and the wall heat flux.Based on the numerical results,the heat reduction coefficient formula and the generalized Reynolds analogy relation of the hemispherical body are proposed.4.In the new scheme of carbonization TPS without surface ablation,the injection of pyrolysis gas causes heat and drag reduction,and the increase of chemical species at the wall.On the basis of the two-dimensional axisymmetric 11-species chemical nonequilibrium turbulent flow model,the 10-species model of carbon sublimation gas and pyrolysis gas combustion（assuming that the geometric surface is not retreated）and the 6-species model of pyrolysis gas combustion of carbon phenolic are respectively introduced,and the two-dimensional axisymmetric 21-species and 17-species chemical nonequilibrium turbulent flow models with pyrolysis gas as the transpiration medium are established,the hypersonic flow numerical simulation program with pyrolysis gas as the transpiration medium is developed,the model and code are verified by typical examples.Considering the relationship between pyrolysis transpiration and wall heat flux distribution,the heat and drag reduction of non-uniform transpiration of carbon phenolic pyrolysis gas on a smooth hemispherical body in hypersonic flow are calculated and analyzed by using 17-species chemical nonequilibrium turbulent flow code.The results show that:the injection and combustion of pyrolysis gas increase the shock wave breakaway distance,reduce the wall heat flux and friction resistance.The heat reduction effect of pyrolysis gas injection and combustion is closely related to the flow condition.The combustion reaction between the pyrolysis gas and the oxidizing components in the incoming stream will release heat,but the increase of the wall heat flux can be ignored.Based on the numerical results,the heat reduction coefficient formula of hemispherical carbon phenolic without surface ablation is proposed.