Numerical Simulation Of Hypersonic Plasma Flow Field And Electromagnetic Wave Propagation Characteristics

Whether it is a reentry spacecraft or a near-space hypersonic vehicle,a shock wave will be formed on the head of vehicle due to the ultra-high speed.Then a high temperature effect and chemical reaction such as ionization will occur,and plasma covering the surface of the vehicle is formed,which is called the plasma sheath.Plasma sheath has a shielding effect similar to that of metals on communication signals.In severe cases,it can cause communication interruptions,this phenomenon is called the "blackout" phenomenon.In order to deepen the understanding of the communication "blackout" phenomenon and provide an effective reference for solutions of communication "blackout",this paper takes the RAMC vehicle as the research object.And the two-dimensional and three-dimensional plasma flow fields of RAMC vehicle and the propagation characteristics of electromagnetic waves are studied.The main work is as follows:Based on the N-S equation and thermochemical non-equilibrium model,the finite volume method was used to numerically simulate the two-dimensional plasma flow field of the vehicle at 61 km.The thermochemical non-equilibrium model is processed by7-component 18-chemical reaction model,and the unstructured grid is designed considering the influence of the boundary layer.Then the grid independence of the designed 2D grid was verified,and the calculation results were compared with flight test data and simulation results of other researchers,which is aimed to verify the reliability of the program and the grid model.The two-dimensional plasma flow fields of the vehicle under 20～90km are calculated,and the distributions of electron number density and electron collision frequency are given.At the same time,considering the uncertainty of the chemical reaction rate caused by the wide temperature range of the chemical reaction model,the two-dimensional plasma flow fields of vehicle under different chemical reaction ionization rates are numerically calculated,and the effects of different ionization rates on plasma sheath thickness,electron number density and collision frequency are analyzed.The three-dimensional plasma flow field of the vehicle at 61 km and an attack angle of 0°is performed.The thermochemical non-equilibrium model for the calculation of the three-dimensional flow field is the same as that of the two-dimensional model,and the unstructured grid is extended from two-dimensional to three-dimensional.The gridindependence of the 3D grid was verified and the simulation results were compared with the flight test data and the calculation results of the two-dimensional flow field to verify the accuracy of the results.On this basis,the three-dimensional plasma flow field of the vehicle at different angles of attack is numerically simulated,and the effects of the angle of attack on the electron number density,pressure,and temperature are analyzed.Based on the calculation results of the above flow field,the propagation characteristics of EM waves in the plasma sheath at different frequencies,reentry heights,polarization modes,incident angles and ionization rates were calculated by solving the multiphysics coupling wave equations.Compared with the traditional SMM scattering matrix method,the calculation results in this paper reproduce the entire propagation process.By analyzing the propagation characteristics of electromagnetic waves in plasma under different conditions,four methods for reducing the amplitude attenuation of electromagnetic waves are obtained.One is to install the antenna as close as possible to the tail of the vehicle,the other is to reduce the ionization rate of chemical reactions,and the third is to reduce the incident angle of electromagnetic waves,the fourth is to increase the electromagnetic wave communication frequency.The related conclusions provide data reference and theoretical support for seeking solutions to mitigate the "communication blackout" phenomenon.