Numerical Investigation For Hypersonic Flow Control By Magnetohydrodynamics Methods

MHD (Magnetohydrodynamics) flow control is a new concept for hypersonic vehicle. In ordinary aerodynamics, flow control has to disturb flow by touching. But in MHD concept, it could be carried out by magnetic field and electric field, with the advantage of not modify configuration of vehicle. In the aerospace community, the MHD research has shown great potential in flow control associated with hypersonic vehicles and propulsion systems. The applications mainly include heating reduction, air capture increase and combustion mixing enhancement.In this thesis, basing on MHD numerical technologies and theoretical analytical methods, hypersonic flow control phenomena and mechanisms were investigated. There are two main parts in this work, research of MHD numerical algorithms and analysis of MHD phenomena.The first part is the research of MHD numerical technologies. MHD flow is distinguished into two types, high Re_m (Magnetic Reynolds Number) and low Re_m. They correspond to full MHD equations and low Re_m equations respectively. Numerical algorithms for these two types were developed.For full MHD equations, aiming at spurious magnetic field divergence problem, equations singularity and conservation problem, a form of eight-waves with source term was proposed. This form has the advantages of eight-wave eigenvectors and monolithic conservation of equations. Numerically, a 3-D Roe solver by means of finite volume formulation, OC-TVD scheme and temporal scheme were applied. 3-D projection scheme was used to modify magnetic field from basic scheme, which could clear the spurious magnetic field divergence effectively.It is simpler in numerical algorithms for Low Re_m MHD equations than that for full MHD equations. In order to capture hypersonic flow field structures clearly, and to improve computational efficiently, a 3-D anisotropic self-adaptive tree mesh technology was built for low Re_m MHD flow simulation. A suit of algorithms for tree mesh were developed, including data structure form for 3-D tree mesh, self-adaptive distinguishing, mergence/ cleavage, and audit for levels of adjacent cells. Some other steps, protective refinement and local mergence/ cleavage control, were used for mesh optimization.Forementioned numerical algorithms were realized in Fortran codes, including FMHD(3-D full MHD code with structural mesh), LSMHD(3-D low Re_m MHD code with structural mesh), LTMHD(3-D low Re_m MHD code with tree mesh). These codes were validated to be accurate by multiple classical MHD problems. It shows they could be used for hypersonic vehicle MHD flow control.The second part is mechanism research for hypersonic MHD flow control. Heating reduction control for flow over blunt and oblique shock control were investigated, and results were compared with that for theoretical analysis.Cases for Mach 5 perfect gas flow over a 3-D blunt were studied. The assumption is that electric conductivity is unique in post-shock area. Simulation results show that shock standoff distance increases significantly. And it shows obvious reduction effect on wall heat transfer in the vicinity of the stagnation point (26% reduction for the interaction parameter Q = 6), but a slight variation on wall pressure.Cases for Mach 15 flow over a 3-D blunt were studied. The altitude is 40km. Models for electric conductivity of air and high temperature chiemical equilibrium relations were developed for MHD simulation. Results show heat transfer in stagnation point is lower than that of perfect gas. Shock standoff distance increases, but it is not insignificantly. There is 24% reduction for the interaction parameter Q = 6.Full-MHD numerical investigation for Mach 10 flow over a perfectly conducting corner was carried out. Shock structure was captured clearly. Results show that magnitude and direction of magnetic field have important impact on MHD effect. Fast-slow shock structure appears in the field in most cases of high magnetic field. When magnetic field vector is perpendicular to free stream, there's no slow shock. These phenomena were all explained by group velocity diagram method.Research for low Re_m Mach 6 MHD inviscous oblique shock was carried out. A partial area of flow field was ionized by electron beam. Results show that the magnetic field compels shock deflexed obviously. Magnitudes of magnetic field and electric conductivity were determinant. When magnetic field vector is perpendicular to free stream, shock deflexes more obviously.MHD control for inlet of hypersonic vehicle is one important application. MHD oblique control was applied to a two-stage Mach 6 inlet. Results show that, when free Mach number is higher than designed, MHD oblique shock control method can be used to change inlet shocks, and make them converging in cowl slip, which is the optimal case desired by designers. With the increase of velocity of free stream, if magnitude of magnetic field increases properly, the optimal case can also realize.