Research On Shock Field Characteristic Simulation And Laser Doppler Frequency Discrimination Method For High-speed Target

The continuous development of supersonic aircraft makes it more and more important to realize the detection and recognition of targets.During the flight of a highspeed aircraft,the head airflow will be strongly compressed to form a shock wave.The change in gas density will change the refractive index and cause the beam to deflect and scatter.It will also attenuate the beam energy.Aerodynamic optical effects can affect tracking,detection,and guidance.Therefore,based on the research background of highspeed targets,the following researches are carried out: research on the distribution characteristics of shock waves,simulation analysis of the scattering characteristics of high-speed targets,and simulation analysis of the speed measurement of high-speed targets.The analysis of shock field in this paper is based on Fluent simulation software.First,the finite element model is briefly introduced,including the description of the NavierStokes equation and the description of the turbulence control equation.Secondly,the simulation model is established and the distribution range of the external flow field is set.The two types of situations with different heights and different velocities are simulated and analyzed,and the density distribution,velocity distribution and temperature distribution of the shock field are calculated.And based on the density distribution,the refractive index distribution of the shock field is obtained based on the Gladstone-Dale relationship simulation,which provides a theoretical basis for the subsequent analysis of the light transmission effect.The scattering characteristics of high-speed targets are developed by calculating the radar scattering cross section(RCS).Use FEKO simulation software,and adopt Mo M method for simulation analysis.The three-dimensional modeling software UG is used to model the target,and the CADFEKO software is used to process the parameters and divide the mesh.The RCS under shock and non-shock conditions are simulated and analyzed.Based on the RCS obtained by simulation,the effect of shock wave on the power of radar echo signal is calculated and analyzed using radar equations,which provides a data basis for the actual radar system parameter design.For the measurement of high-speed target speed,the Doppler frequency discrimination method based on the phase modulation method is used.First,a brief answer is given to the design of the speed measuring radar system.Secondly,the principle of the phase modulation method and the frequency discrimination process are described.The method uses the cooperation of the F-P etalon and the phase modulator to complete the speed analysis of the high-speed target.On the basis of obtaining the basic theoretical model,the DC signal is used to enhance the measurement range.At the same time,a method of normalized amplitude is proposed to further expand the frequency discrimination range of the measurement system.The frequency discrimination curve is analyzed in depth,and the normalization is verified by simulation The amplitude method can effectively improve the dynamic measurement range,and can achieve the speed measurement of high-speed targets.