Computational Investigation of Aero-Optical Distortions in a Free Shear Layer

*† ‡ A computational study of an unforced and periodically forced two-dimensional shear layer behind a backward facing step is presented. The goal is to investigate the optical aberrations caused by large and small scale structures in the flow field. Fluid dynamical as well as optical data was used to correlate the flow structures with the optical distortions. Simulations using the compressible Navier-Stokes equations were used to directly compute the unsteady density field. This density data, as well as the computed Optical Path Difference, is analyzed using Proper Orthogonal Decomposition to determine the optically detrimental structures which are the eventual target of feedback flow control. The investigations showed that POD of the density is a well suited tool for this analysis since its changes are largest in the optically detrimental coherent structures in the shear layer.