Air Disturbance Caused By Carrier Motion And Its Effect On Laser Propagation

Lidar is gradually applied to aircraft,rockets and other moving carriers,and has realized the function of target detection or advanced ground measurement.In such applications,the high-speed motion of the carrier platform will cause the disturbance of the surrounding air,leading to the uneven change of the refractive index of the air,which will affect the propagation process of the laser radar detection beam,and cause the optical path change,spot deviation,energy attenuation and other problems of the imaging beam,thus affecting the detection performance of the laser radar.For this reason,the finite element method is introduced in this paper to study the local air disturbance caused by the high speed motion of the lidar mounted carrier and its effect on the propagation of the detection beam,which provides a theoretical basis for the study of the detection performance of lidar in the high speed motionenvironment and thesystemoptimization.On the basis of in-depth data investigation,the calculation model of the local disturbance field caused by the high-speed movement of the carrier and the analysis method of the beam propagation is introduced,and the modeling of the moving carrier,meshing and the simulation method of the air disturbance field using ANSYS software is conducted in this thesis.On this basis,the author considers the laser radar in the application of the high-speed motion carrier such as aircraft and missiles,respectively by using 2D and 3D model of wing and blunt cone two kinds of typical laser radar carrier air density field disturbance caused by high speed movement simulation,presents a different speed,angle of attack,height and so on different stages of the quantitative distribution of air density field,discussed the different airfoils and three-dimensional blunt cone section on the influence of air turbulence field density distribution.In order to analyze the influence of air disturbance field on the propagation of detecting beam,the G-D formula is introduced to convert the density field of air disturbance to the refractive index field,and the scattered data of refractive index points are transformed into uniform grid data by uniform grid division.When the flight altitude is 4km and the speed is 2.8Ma,the maximum refractive index of the disturbance field can reach 1.0007.On this basis,the influence of air disturbance caused by wing motion on the optical path difference of detection beam is calculated by using ray tracing method.It shows that the larger the Mach number is,the lower the altitude is,the greater the air disturbance is,and the greater the influence on the laser propagation process is.The spatial distribution of light field after the beam passes through the air disturbance field is calculated by using diffraction theory,and the influence of the carrier velocity and the incident angle on the spatial distribution of the light field is discussed.It is found that the existence of the air disturbance field will cause the obvious deviation of the light beam.In addition,the theoretical calculation results of the blunt cone carrier are compared with the spatial distribution of the refractive index of the air disturbance field obtained from the wind tunnel test under the same conditions,which verifies the correctness of the theoretical calculation method and results.The experimental results of beam deflection caused by airflow disturbance at different velocities are also given.The results show that the smaller the angle betweenthe airflowand thebeampropagation direction is,thesmallerthebeamdeflection is.