Numerical Research On Supersonic/Hypersonic Plasma Flow And Its Electromagnetic Characteristics

These are momentous subjects on the strategic missile defense penetration in military region and mastering the interruption of communication for hypersonic reentry vehicle in astronautic project. The dissertation carries out several researches on the subjects. And the results should be a significant technical support for correlative research and design.The theoretical foundation of the dissertation is the interaction mechanism of the electromagnetic wave and the plasma flow field which includes plasma sheath and plasma wake of the reentry vehicle. The magnetohydrodynamics (MHD) equations, which coupled by fluid mechanics equations and electrodynamics equations, are applied to solve the interaction problems of electromagnetic wave and plasma fluid. Considering the computer performance and the computational efficiency, solving the MHD equations by numerical simulation technique is very difficult. To solve above difficulties and make the research on the interaction mechanism of electromagnetic wave and plasma simplify, based on the magnetohydrodynamics theories, this dissertation obtains nondimensional MHD equations and analyzes the magnitude of coupled terms in the MHD equations. At the height of theory, it is the first time to prove that the fluid mechanics equations and the electrodynamics equations can be decoupled from the MHD equations under the current radar output power.The research on the interaction mechanism of electromagnetic wave and plasma will be carried out on the premise of the thorough understanding of the electromagnetic parameters characteristics of plasma sheath and plasma wake. According to that truth and the decoupling conclusion, based on the lasted achievements of hypersonic numerical simulation technique, adopting the 11 species,20 reactions chemical model and the two temperature model, the finite volume method and LU-SGS implicit method are chosen to solve the full Navier-Stokes equations. The computational code has been established and converted into a software module. The computational results are consistent with those of the references and the code has been validated using experimental data. The hypersonic flow over sphere and blunted cone has been simulated, and the results have been analyzed thoroughly. On the basis of the hypersonic flow field, the reentry conditions that the ionization gas coating the hypersonic vehicle can be treated as plasma have been obtained and the reentry plasma model has been established.Some algorithms which are used to solve electromagnetic wave propagates in plasma have been discussed detailedly in this dissertation. To improve the computational efficiency of finite difference time domain (FDTD) method, combining piecewise linear recursive convolution (PLRC), JE convolution (JEC) method with alternating direction implicit (ADI) technique, the PLRC, JEC-ADI-FDTD methods have been deduced. The stability conditions, grid size and other critical techniques have been analyzed in detail. The computational codes which are designed to analyze the interaction characteristics of the full band electromagnetic wave and nonmagnetized plasma have been established by using PLRC, JEC, PLJERC-ADI-FDTD methods and have been converted into a software module. The computational results are consistent with those of the references and the codes have been validated by references.Based on the typical hypersonic flow results computed by the thermochemical nonequilibrium code, applying the FDTD codes, the characteristics that the electromagnetic wave propagates in the reentry plasma and the influence of reentry plasma on radar target characteristics have been computed and analyzed contrastively. It is the first time to have obtained the backward radar cross section (RCS) characteristics that vary with the fluid mechanics parameters:Re, Ma/Re^1/2, and analyzed the influence of flow pattern upon radar target characteristics of reentry vehicle. The interaction mechanism of electromagnetic wave and reentry plasma has been researched, and the feasibility of plasma stealth has been validated by numerical simulation.The working principle, plasma generating method and stealth efficiency of different plasma stealth techniques have been reviewed. In general, the wake is turbulent flow generally. Considering that, it is the first time to put forward the idea of plasma eddy stealth and study the stealth mechanism of plasma eddy. To generate plasma eddy, the code for the computation of turbulent flow has been established based on the large eddy simulation (LES) technique and has been converted into a software module. The process of the eddy generating and developing in free shear layer has been gained. And the conformation characteristics of eddy have been obtained. The FDTD codes are also applied to simulate the characteristics that the electromagnetic wave propagates in plasma eddy. Based on the numerical results, conclusions can be deduced that the electromagnetic wave can be absorbed effectively by plasma eddy and the plasma eddy has good stealth performance.In conclusion, three software modules have been established and integrated for the study of the supersonic/hypersonic plasma flow and its electromagnetic characteristics in this dissertation. The integrative software module can be applied to simulate the hypersonic flow over vehicle and the movement of turbulent eddy, to provide aerodynamic characteristics of vehicle and the electromagnetic parameters distribution characteristics of flow field. It can also provide the technical support for the design of aerodynamic layout and thermal protection of hypersonic vehicle, and provide flow data for the research on reentry defense penetration and interruption of communication. Furthermore, the integrative software module can be applied to numerically simulate the interaction characteristics of electromagnetic wave and plasma flow field, to carry out the research on the interaction mechanism of electromagnetic wave and reentry plasma, and the stealth mechanism study of plasma. Some results and conclusions in this dissertation can provide the technical support for the design of reentry defense penetration and for the mastering of the interruption of communication.