| Infrared imaging detection and guidance system plays an important role in hypersonic vehicle’s environment perception system.Up to now,the aero optical effect caused by the strong interaction between the aircraft wall and optical window and the high-speed flow is still the main factor restricting the application of infrared imaging detection system in hypersonic vehicles.Wind tunnel experiment and computer simulation are the common ideas to study this problem.Due to the problems of low efficiency,high cost and lack of experimental samples in wind tunnel experiment,the establishment of reasonable computer simulation model can quickly provide a large amount of data support for the research of aero optical effect,thus greatly reducing the research cost.In order to obtain real and reliable simulation data,it is very important to establish an accurate calculation model.In this paper,aiming at the optical transmission effect of hypersonic optical side window jet cooling aerodynamic flow field,the flow field density data are obtained by using FLUENT software,and the imaging simulation and evaluation of the aerodynamic optical transmission effect are completed by using a new 3D cellular automata flow field ray tracing algorithm,combined with the offset matrix and optical system aberration theory.The main research work of this paper is as follows:(1)To solve the problem of inaccuracy of the existing hypersonic flow field simulation research model,this paper establishes a blunt cone external flow field calculation model with optical side window and cooling jet nozzle by means of ANSYS Workbench 19.2 finite element analysis software kit,and makes more accurate numerical calculation for several cases at different flight altitudes,speeds,angles of attack and at different times.The characteristics of the air flow and the external flow field of the cooling jet nozzle under different flight conditions are analyzed.The results show that the lower the flight height,the higher the flight speed,the smaller the angle of attack(the absolute value is higher when the angle of attack is negative),and the larger the initial pressure of the cooling jet.(2)Light tracing is one of the important means to study the aero-optical effect.In this paper,the shortcomings of ray tracing method based on refractive index layer or partition and refractive law and light tracing method based on light equation and refractive index gradient are pointed out through theoretical analysis.Then,based on three-dimensional cellular automata theory and geometrical optics theory,a new flow field ray tracing algorithm is proposed,which can maintain the calculation accuracy and improve the calculation efficiency.Finally,the new light tracing algorithm is implemented using C++ language programming.The spatial distribution and optical path data of infrared radiation in the flow field above the optical window are obtained by using the new ray tracing method.(3)The imaging distortion,blurring,jitter and energy attenuation caused by aero-optical effect are simulated,and the effects of different flight conditions on aero-optical effect are analyzed.Firstly,the offset matrix and wavefront aberrations under different flight conditions are obtained by using the image plane offset data and the optical path data obtained by ray tracing.Then,the simulation models of aero optical distortion,blur and energy attenuation effects are established by using the offset matrix,point spread function and Strehl ratio respectively.Based on the above methods,the aero optical transmission effects at different times,namely aero optical jitter effect,are calculated.Finally,based on SSIM image distortion evaluation algorithm,we get the conclusion that the lower the flight altitude,the faster the speed and the smaller the angle of attack,the more significant the aero optical transmission effect is. |
PDF Full Text Request