Two-dimensional numerical simulation of shear-layer optics

Abstract

Two-dimensional Euler equations are solved directly using the second-order, explicit, MacCormack predictorcorrector and Godunov methods alternately for the investigation of free-shear-layer optical properties. The optical effects of coherent structures in the mixing layer are identified. As expected, far-field optical quality of a laser beam is degraded the most when a laser beam passes through the edge of the large eddies. The far-field optical performance can be improved significantly by controlling the coherent structures in the mixing layer. The growth of shear layer is retarded by fundamental frequency forcing, and it is found the Strehl ratio is the highest in the nongrowth region.

Physics and Computation of Aero-Optics

“…Beam jitter was modeled, and high-order distortions were largely unaccounted for. Tsai & Christiansen (1990) solved Euler equations numerically to study the degradation of a laser beam by a plane mixing layer at low Mach numbers (M 1 = 0.2 and M 2 = 0.1 for the two air streams). Their solutions were able to capture qualitative features of large-scale coherent structures including vortex pairing, but this is a result of the numerical viscosity in the simulation code based on a combination of MacCormack and Godunov methods.…”

Computational study of optical distortions by separated shear layers and turbulent wakes

“…Cassady, Birch & Terry (1989) obtained unsteady two-dimensional solutions for compressible flow over a cavity and analysed its induced optical distortion. Tsai & Christiansen (1990) solved two-dimensional Euler equations for a free shear layer and studied the effects of flow forcing on optical distortions. More elaborate approaches involved Reynoldsaveraged Navier-Stokes (RANS) calculations using a turbulence model such as the k-ε model.…”

Research Advances in Aero-Optics Adaptive Correction

“…系， 相干结构与光束相互作用模型可以表示为如图 11 所示的简化模型 [53] 。 1982 年 ， Oster 和 Wygnanski 研 究 表 明 [65] [62] 以 及 Tsai 和 Christiansen 相 关 的数值研究 [66] 表明： 通过一定周期激励改变相干结构的力学参量会伴随着 -…”

“…式中 f 为基波频率，θ 为剪切层的初始动量厚度，Ū 为剪切层平均对流速度。 1985 年， Roberts 等发现： 相对于无扰动流场， 加入剪切层 280 Hz 基波扰动后， 在频率锁定区域(即剪切 层 的 增 长 率 为 0 的 区 域)， -R S 值 从 0.66 增 加 到 0.91 [73] 。 1989 年 ， Tsai 和 Christiansen 基 于 欧 拉 方 程 数 值 计 算 速度分别为 70.4 m/s 和 35.2 m/s 的二维非定常可压缩剪切层流场的流场参数分布、 基于光线追迹计算了 "近 场 " 的 相 位 分 布 、 基 于 物 理 光 学 方 法 计 算 口 径 为 2.56 cm 的 He-Ne 激 光 的 远 场 分 布 [66]…”