Guo Guangming, Tong Xiaojian, Luo Qin
Appl Opt. 2020 Dec 10;59(35):11059-11069. doi: 10.1364/AO.409548.
The supersonic mixing layer over the optic window of a high-speed imaging guided vehicle is the primary turbulent flow causing aero-optical effects such as the target image blurring, jittering, and offsetting. Employing the large eddy simulation and ray tracing methods, this paper presents a numerical investigation on target image degradation of a beam passing through the supersonic mixing layer under different conditions. The distorted wavefront, degraded target image, and peak signal-to-noise ratio of the degraded image are proposed to quantitatively evaluate the target image degradation. On the whole, the degraded target image is mainly shown as image blurring, and the larger the convective Mach number of the flow field, the more severe the image degradation. It is found that the beam incident position should be away from transition area of the supersonic mixing layer for a clearer image, the larger inlet fluid density difference results in a more severe target image degradation due to the stronger density fluctuation of turbulent flow structures, and the optimal beam incident angle is about 30° for the current calculation conditions.
高速成像制导飞行器光学窗口上的超声速混合层是导致诸如目标图像模糊、抖动和偏移等气动光学效应的主要湍流。本文采用大涡模拟和光线追踪方法，对不同条件下光束穿过超声速混合层时的目标图像退化进行了数值研究。提出了畸变波前、退化目标图像以及退化图像的峰值信噪比来定量评估目标图像退化。总体而言，退化的目标图像主要表现为图像模糊，流场的对流马赫数越大，图像退化越严重。研究发现，为了获得更清晰的图像，光束入射位置应远离超声速混合层的过渡区域；由于湍流结构的密度波动更强，入口流体密度差越大，目标图像退化越严重；在当前计算条件下，最佳光束入射角约为30°。
