Reseach On Ray Transmission Through Aero-Optical Window Based On Self-Adaptive-Mesh Method

While the high-speed aircrafts flying in the atmosphere, the window of the aircraft interacts intensively with the coming flow, causing kinetic energy transform into heat energy. The temperature inside the window increases, and the deformation occurrs in the window. Moreover, the irregular and non-uniform refractive index field is formed in the window, leading to the seriously aero-optical effects of the window. After passing the distortional window, the wavefront will deviate from the ideal plane wavefront, generates additional phase, affects the imaging quality seriously. Therefore, the image is offset and fuzzy, reducing the capability of tracking, detecting, and identifing of the high-speed aircraft, which also will reduce the guidance precision greatly.Based on the characteristics of the refractive field of the aero-optical window, the adaptive grids method was proposed to simulate and analyze the ray transmission in the window to investigate the effects of the aerodynamic thermal environment on the imaging quality of the windowt in this thesis.First of all, based on the original meshes, the adaptive meshes were generated according to the refractive index field. Secondly, the ray tracing step was determined according to the grid size which the point is in. Finally, the ray tracing was simulated using the fourth-order Runge-Kutta algorithm, and the optical paths of each ray in the exit pupil were obtained, which provided the basis for further evaluation of imaging quality and wavefront correction of the window.A ray tracing software under the Visual C++ environment was developed, and different optical evaluation functions were compared when different theresholds for grid division and ray tracing steps for ray transmission were used, such as the PSF, MTF, Strehl ratio, encircled energy, distortional image, wavefront tilt, wavefront variance, and so on. After considering both the caculating time and ray tracing precision, the optimum threshold for grid division and ray tracing step were selected. And the images were analyzed at different incidental angles.Besides, a refractive index field was generated in this thesis, the simulation results obtained from the software were compared with the theoretical results obtained from the formula to analyze the precision of this simulation software.