Study Of Electromagnetic Wave Propagation In Hypersonic Vehicle Plasma Sheath

When the hypersonic vehicle enters the atmosphere,enormous amount of heat will be emerged by the friction between vehicle and atmosphere,and shockwave will be generated at the head of the vehicle with drastic chemical reactions.Finally,the plasma sheath will be formed around the surface of the vehicle,which will absorb electromagnetic waves and affect the quality of communication,even leading to communication interruption,which is called as blackout.In order to solve the blackout problem of hypersonic aircraft,take RAM-CII aircraft as research object,systematically analyze the characteristics of hypersonic plasma sheath.The transmission features of electromagnetic wave in the plasma sheath are also discussed.The main contents of the thesis are as follows:(1)Based on the numerical calculation method for solving the fluid governing equations,numerical calculation software FASTRAN is used.By introducing the two-temperature model and the chemical nonequilibrium reaction model simultaneously,the discrete solution of the plasma sheath at the head of the aircraft is calculated.The parameter distributions of the plasma sheath at 61 km and 71 km altitudes are obtained,and the numerical results are verified by analyzing the parameters such as temperature and mass fraction of the plasma sheath.Then,combined with the flight test data,the plasma sheath of the RAM-CII aircraft under typical flight conditions in the altitude range of 24km-84 km is numerically solved,and the effects of electron number density and collision frequency with the reentry altitude are analyzed.(2)Based on the calculated plasma sheath data in the reentry process,the transmission attenuation of 259 MHz electromagnetic wave under various reentry conditions is obtained by using the WKB(WentzelKramers-Brillouin)transmission model.It is found that there is a communication blackout from 84 km to 24 km high.The effects of the external magnetic field,antenna position and electromagnetic wave frequency on transmission attenuation are analyzed.The results showed that under the external magnetic field,the dextrorotatory round polarization wave with magnetic induction intensity of 1T can diminish the communication blackout;The closer the antenna position is to the tail of the aircraft,the smaller the attenuation will be.Changing the antenna position can alleviate the communication blackout;Changing the frequency of the incident electromagnetic wave can reduce the communication attenuation,especially the laser communication,which provides a viable idea to solve the blackout problem.In this paper,the characteristics of the hypersonic plasma sheath and the transmission characteristics of the electromagnetic wave in the plasma sheath are studied,which provide the reference for alleviating the blackout.