Numerically Simulate Aero-Force&Heat Of Hypersonic Vehicles And Region Marching Method For Supersonic Flow Simulation

The aims of this thesis are studying methods for accurate simulating aerodynamic heat&force of hypersonic/supersonic flows and the efficient numerical method for hypersonic/supersonic flows. There are two parts of works included in this thesis. The first part is the technologies of accurately simulating aerodynamic force and aerodynamic heat of supersonic flow and its applications in predicting the aerodynamic force and aerodynamic heat of hypersonic vehicle. The second part is the high efficient methods in solving supersonic flow, they are space marching and region marching methods, and their applications in solving complex engineering problems and in automatical aerodynamic optimization design.Studying work related to accurate numerical simulation of aerodynanic force and heat and its apllications are as follows:There is comparatively large velocity gradient between flow and solid surface in supersonic flow field, which leads to large velocity and temperature gradients producing comparatively large skin friction and aerodynamic heat. At the same time, there are laminar and turbulent flow conditions in most of supersonic flows. Numerical simulating technologies must have sufficient accuracy to predict the velocity and temperature gradients in laminar and turbulent conditions for accurately predicting the aerodynamic heat and force.The time dependent methods of this thesis use cell-averaged finite volume techniques to solve the conservative form governing equations on structured grid. LU-SGS method is used in time-marching. In space terms difference, inviscid fluxes construction use third order MUSCL interpolation method and AUSMPW+ scheme, viscous fluxes use central difference method which base on the Gauss Law. Turbulence simulations use Kok's modified k ?ωTNT 2-equation turbulence mode coupled with an advanced wall function boundary condition considering modification of compressibility and heat transfer and being valid in whole turbulence boundary layer.Basing on the techniques introduced above, the accurate wall skin friction and wall heat flux can be gotten for laminar flows (normal grid Reynolds number Re n<80 for hypersonic cylinder flow) and for the turbulence flows (y+<200~300 assuming the constant shear stress hypothesis in the lower part of the boundary layer etc.) . For accurately predicting hypersonic vehicle's flow fields, the characteristic flows in hypersonic vehicles are confirmed and validated by present CFD tool. The aerodynamic force and heat of a hypersonic vehicle are predicted in the power off, cruise conditions basing on the numerical confirmations described above. Wall heat flux and its maximum locations are obtained. In the maximum heat flux region, the maximum heat flux can beyond 3MW/m2. At the same time, aerodynamic force characters are acquired. The skin friction force, including inner inlet and combustion chamber friction force, possesses 62.7% of the whole drag force. Those data is very crucial to the heat protection and aerodynamic design of hypersonic vehicles.Studying work related to pseudo-temporal space marching methods and region marching methods for complex supersonic flows and their applications are as follows: As having obtained accurate numerical prediction abilities for aero force and heat flux of supersonic flows, space marching ability of supersonic dominated flow field is fulfilled. Space marching methods use pseudo-temporal iteration and iteratively solve parabolic NS equations in the marching plane. The time iterating method in the marching plane uses modified LU-SGS methods. Inviscid fluxes of the space marching direction use first order or second order upwind difference. The construction of normal direction and spanwise inviscid fluxes uses third order MUSCL interpolation and AUSMPW+ scheme. Viscous and dissipation fluxes in the space marching direction are neglected and the remainder directions dissipation gradients of viscous fluxes are constructed basing on Guess Law. Space marching techniques are successfully used in supersonic dominated inviscid, laminar, turbulence and multi-species finite rate chemical reaction flow fields in 2D/3D and axisymmetric cases. Numerical results show that the space marching algorithms are agree well with experiment and have the same level of accuracy in solving supersonic dominated flow fields in comparison with time iteration methods, furthermore, present space marching algorithms are 1~2 orders faster than time iteration methods.For complex supersonic flows, region marching methods are established and used in engineering problems. The region marching methods for complex supersonic flow fields divide the flow field in streamwise direction into supersonic flow dominated regions or reverse and subsonic flow dominated regions according to their physical characters. In the supersonic flow dominated region, flow field is solved by space marching algorithms and in the reverse and subsonic flow dominated region time iterating method is used. The 2D characteristic complex supersonic flow fields are solved using region marching methods. It shows that region marching method have the same level of accuracy as time iterating algorithms in dealing with complex supersonic flow, furthermore, region marching method accelerate the convergence speed several times compared with time iterating algorithms. The 3D inlet and hydrogen fueled Scramjet engine of hypersonic vehicle and 2D kerosene fuled whole areo-breathing engine are numerically simulated with region marching method to illustrate its high efficiency and easily using in complex engineering problems. The region marching results have good agreements with experimental results and time iterating results. Considering about the computational efficiency, for 3D hydrogen fueled Scramjet case, it takes 5 days with 256 CPU processors (0.8GHz) to get on condition's result for time iterating algorithm in the entire flow field. But it only takes 3 days with 1 CPU processor in the space marching regions and 8 CPU processors (2.8GHz) in the time iterating regions to get the same result for region marching method.Because it's high efficiency and easy using and accuracy, region marching method is used as the turbulence CFD analysis tool during the cycle of automatic design optimization. Combined with parametric description of optimization geometry and automatic grid generation, single and multi-objects automatic optimizations of single expansion ramp nozzle (SERN) of hypersonic vehicle are fulfilled using the sophisticated optimization tools. Because of using cheap and accurate CFD analysis software, only about 40 seconds are needed for one optimization cycle and 11 hours are needed for about 1000 optimization cycles. The optimization procedures can run quickly in a single CPU processor. The lift and propulsion force of the nozzle have improved significantly after the optimization.Seven chapters are included in this thesis. The First chapter is the introduction. The meaning and development of researching work are introduced. In chapter 2, time iterating algorithms are introduced and wall function boundary conditions and thermally perfect gas model are validated. In the third chapter, the aerodynamic force and heat flux of the hypersonic vehicle and the characteristic flow conditions of hypersonic vehicle are simulated, those work provide reliable datum of heat flux and aero-force for engineering design. In chapter 4, the space marching algorithms of supersonic turbulent and chemical reaction flow included their validations are fulfilled. In chapter 5, the region marching method for complex supersonic flow fields and their applications in engineering problems are fulfilled. In chapter 6, combining region marching method for solving supersonic flow fields, automatic optimization design of hypersonic vehicle's SERN nozzle is conducted. Chapter 7 is the conclusion of this thesis.