Numerical Simulation Research On Hypersonic Aero-heating

Hypersonic vehicles have received more and more attention because of their remarkable commercial and military values.A large number of technical researches related to hypersonic vehicles have been carried out in many scientifically advanced countries.The accurate prediction of hypersonic aerodynamic heating plays a very important role in guidance and reference for the design of hypersonic vehicles.The application of Computational Fluid Dynamics(CFD)for aero-heating simulation is represented as a discrete solution of the governing equations of continuous flow,Navier-Stokes(N-S)equations.The most widely used numerical discretization method is Finite Volume Method(FVM).The numerical simulation of aero-heating is affected by many aspects,such as discrete scheme,mesh correlation,real gas effect,rarefied gas effect and turbulence model.These factors lead the numerical simulation of aero-heating to one of the difficulties in CFD.So,the research on hypersonic aerodynamic heating is of great significance in the improvement of hypersonic vehicles design.There are many restriction factors on hypersonic aero-heating accurate simulation.The finite volume method is employed to research three aspects of these factors which contain mesh correlation,discretization scheme and real gas effects in this paper.The research on influence of unstructured/hybrid mesh type and mesh size for computation results of heat flux is carried out.Definition methods of the principle direction for Gnoffo's multidimensional inviscid flux reconstruction are studied,which is employed for the hypersonic aero-heating simulations on tetrahedral grids.The simulation of aero-heating in chemical nonequilibrium flow is studied by the unstructured cell-vertex FVM.In addition,effects of surface catalysis efficiency on aero-heating characteristics in thermo-chemical nonequilibrium hypersonic flow are studied.The main research contents of this paper are summarized as follows:(1)Mesh correlation for aeroheating simulation on unstructured/hybrid grid is studied.Numerical investigation for the hypersonic flow around a cylinder is performed by using the unstructured FVM solver in which the STVD scheme is employed in inviscid flux reconstruction.The effect of the mesh type in zones of shock and near surface and the other zones on heat flux simulation is studied.Based on this,the numerical investigation of the heat flux accuracy influenced by the mesh size near the wall is studied.(2)The effects of the principle direction definition method for Gnoffo's multidimensional inviscid flux reconstruction on hypersonic flowfield are studied.The analysis for the results in which the principle direction defined method based on Cartesian directions,density gradient and pressure gradient shows that the phenomena of carbuncle and pressure contour 'zigzag' occur in the flowfield.Thus,a hybrid method based on pressure function as a shock indicator is proposed to define the principle direction in this paper.Thus,results of flowfield and surface heat flux for this hybrid method are analyzed.(3)The method used in unstructured cell-vertex scheme for surface catalytic boundary conditions in chemical nonequilibrium flow is proposed.In order to solve the nonphysical phenomenon when cell-vertex scheme is implemented in fully catalytic surface,the'relaxation' method for implicit matrix on boundary is developed in this paper.The analysis of simulation results based on this 'relaxation' implicit method is performed.Based on this,the research on the influence of simulation results by the mass fraction is studied.Finally,the numerical methods for finite catalytic and non-catalytic surface boundary conditions in hypersonic chemical nonequilibrium flow are proposed and the simulation cases are presented.(4)Research on the effects of surface catalysis efficiency on aeroheating and flowfield characteristics in thermo-chemical nonequilibrium hypersonic flow is performed.The influence by catalysis efficiency is numerically investigated by the structured gird solver through changing the catalytic recombination coefficient.Simulations are implented for aircrafts with zero and nonzero attacks and the forebody of re-entry capsule.It is indicated that the grid in which hexahedron mesh is used in shock layer zone and cell Reynolds number on the wall within 10 can give best heat flux result.The developed hybrid method can not only eliminate the carbuncle phenomenon,but also remove the pressure contour 'zigzag' phenomenon.In addition,the 'relaxation' implicit matrix method can eliminate the nonphysical result for fully catalytic surface.Also,reasonable results are obtained for finite catalytic and non-catalytic surface conditons.Finally,the numerical investigations for the effects of surface catalysis on thermo-chemical nonequilibrium flow under radiative equilibrium wall indicate that the catalytic recombination coefficient only influence the mass fraction of species and the heat flux is limited.