| In recent years,the potential value of near space hypersonic vehicles in military and communication fields has attracted more and more attention from scholars at home and abroad.Hypersonic flight target refers to the aircraft flying at a speed greater than 5 times the speed of sound.It is widely used in aerospace and other fields.It has the advantages of fast attack speed and difficult detection and capture.It plays an important role in a country’s voice and strategic deterrence.In the process of hypersonic target flight,the friction between the incoming flow and the aircraft surface will produce extremely high temperature and pressure,and a layer of shock wave will be formed on the surface of the aircraft.In this region,due to the effect of high temperature and high pressure,molecules will have a series of reactions,which will produce plasma through the process of dissociation and ionization,which is called plasma sheath.Plasma sheath has a great influence on the transmission and scattering of electromagnetic wave,so the study of the interaction between electromagnetic wave and plasma sheath has always been an important research topic.With the research on the characteristics of plasma sheath and the interaction between plasma sheath and electromagnetic wave,scholars found that the turbulence effect has a significant impact on temperature,pressure and other factors,and the turbulence effect in the plasma sheath has gradually become a hot issue.In this paper,a three-dimensional blunt cone model of hypersonic flow is established to simulate the turbulent flow around it.Firstly,in order to verify the reliability of the simulation results of the turbulence model,the flight scene with the altitude of 61 km and Mach number of 23.9mach was selected in the flight experiment of ram-c Ⅱ.The chemical composition of the air is 79% nitrogen and 21% oxygen.The park 85 dual temperature model is used to select the turbulence model which fits well in solving the hypersonic flow field problem.The results show that: the change trend of electron number density of turbulence model simulation results is basically consistent with the flight experiment results,which shows that the turbulence model in this paper can get better simulation results,which provides a reliable basis for the turbulent flow field of hypersonic target calculated in this paper.In the simulation of hypersonic target flow field,this paper analyzes the similarities and differences between the conventional laminar flow model and the turbulence model.The results show that there are significant differences in electron mass fraction,pressure,temperature and electron number density between laminar flow model and turbulence model.The wave system structure of the gradient variation of each parameter is basically the same,but the extreme value of each parameter and the boundary layer of each gradient are significantly different.Based on the analysis and summary of the simulation results of the flow field,the reasons and rules of the difference of the flow field parameters between the turbulence model and the laminar flow model are given.In order to explore the influencing factors of turbulent flow field,the effects of different heights and Mach numbers on the parameters of turbulent flow field were analyzed.use k-ω? turbulence model,the results show that: the change of height has a significant impact on pressure and temperature.With the increase of height,the air density will obviously decrease,resulting in a great difference in pressure.The higher the height is,the lower the pressure is.However,the pressure reaches the extreme value in the stagnation point region of the head and gradually decreases along the stagnation point line.The influence of height on temperature is not as big as that of pressure,and the wave structure of gradient change is large To the same.The influence of Mach number on pressure and temperature is also significant,and the influence on temperature is more significant than that of different heights.In this paper,the radar cross section of the target is calculated based on the above flow field simulation results.Firstly,the flow field parameters are transformed into the dielectric constant and other parameters in electromagnetic calculation through the multi physical coupling of flow field and electromagnetic field,and then the finite difference time domain method of dispersive medium is used for simulation calculation.Finally,through the comparison of RCS results,different plasma parameters,with or without plasma sheath,different velocity,different height,different incident angle and different incidence are analyzed The influence of different factors such as wave frequency on radar cross section. |
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