Numerical Simulation 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 wave-front aberrations in an optical beam passing through a supersonic open cavity flow. The turbulence model blends a Reynolds-averaged Navier–Stokes-type closure near solid walls with a subgrid model in the freestream 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 wave front are computed; these 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 wave front spanning the entire cavity reveals that wave-front distortions are driven by shear-layer oscillation at the Rossiter frequencies; these disturbances create eddy shocklets that propagate into the freestream and create additional optical path disturbances.