Modeling And Scattering Analysis Of Reentry And Plasma Sheath

The process of returning to the Earth’s atmosphere after the aircraft enters outer space is called the reentry process.This type of aircrafts is also known as the reentry body.Since the reentry body flies at an extremely high speed in the atmosphere（up to Mach 24）,a strong air compression effect occurs around the windward surface and a shock wave is generated.There is a strong viscous friction between the shock wave and the atmosphere,which makes the air temperature around the reentry body rise rapidly.The high temperature will lead to the dissociation and ionization of the air,and the heat-resistant material on the surface of the reentry body will be ablated.The reentry body is therefore surrounded by this high temperature plasma with a peak electron density of10¹³10^{1 6}cm^-3.This plasma region,also known as a plasma sheath,has important effects on the transmission of electromagnetic signals and electromagnetic scattering properties.This thesis focuses on the blunt cone model（code RAM C-II）in the Radio Attenuation Measurement（RAM）experiment,and the research content can be divided into two parts.The first part numerically solves the Navier-Stokes equations to obtained the flow field data of the reentry body.In the second part,the electromagnetic scattering data of the reentry body under various factors are calculated,and the influence of the plasma sheath on the electromagnetic scattering characteristics of the reentry body is analyzed.For the part of the reentry flow field,the dual temperature model is chosen to describe the thermodynamic state of the particles,and Park’s 7-component chemical reaction model is employed to describe the dissociation and ionization processes of the gas components.The Naiver-Stokes equations with chemical sources are used to describe the thermochemically non-equilibrium spoiler flow field around the reentry body during the reentry process,and the numerical methods of Flux Difference Splitting（FDS）is used to solve the equations.In this thesis,the same flight conditions of the RAM C-II experimental data are simulated and the simulation results are in good agreement with the experimental data,which verifies the reliability of the flow field calculation.This thesis also simulates and calculates the flow field parameters of RAM C-II under different flight conditions,and studies the influence of flight altitude and flight speed on the flow field parameters.For the electromagnetic scattering part,the influence of different flight conditions on the plasma frequency and collision frequency of the flow field is first analyzed.The relative permittivity of the plasma sheath in different states are calculated using the numerically simulated flow field data.For the difference between the fluid field grid and the electromagnetic grid,this thesis introduces a method of grid information conversion,which converts the relative permittivity data on the fluid field grid to the electromagnetic field grid.Finally,the radar cross sections of the target are calculated,the influences of the plasma sheath on the scattering properties are examined.This thesis also compares the radar cross sections under different flight conditions,different incident wave frequencies and different angles,and studies the influence of these factors on the scattering characteristics of the reentry body.