LES/RANS Modeling of Aero-Optical Effects in a Supersonic Cavity Flow

Abstract

A hybrid Large Eddy simulation / Reynolds-Averaged Navier-Stokes turbulence model is applied to compute the wavefront aberrations in an optical beam passing through a supersonic open cavity flow. The turbulence model blends a RANS-type closure near solid walls with a subgrid model in the free-stream based on the ratios of estimated inner and outer turbulent length scales. The cavity geometry is modeled using an immersed boundary method, and an auxiliary flat plate simulation is performed to replicate the effects of the wind-tunnel boundary layer on the computed optical path difference. Two-dimensional proper orthogonal decomposition modes of the optical wavefront are computed and compare favorably with wind tunnel data despite uncertainties about inflow turbulence levels and boundary layer thicknesses over the wind tunnel window. Dynamic mode decomposition of a planar wavefront spanning the entire cavity reveals that wavefront distortions are driven by shear layer oscillation at the Rossiter frequencies; these disturbances create eddy shocklets that propagate into the free-stream and create additional optical path disturbances.