Wall-Modeled Large-Eddy Simulations of Mach 8 Turbulent Boundary Layer and Computation of Aero-Optical Distortions

Abstract

Compressible wall modeled large-eddy simulations of a Mach eight turbulent boundary layer over a flat plate were carried out for the conditions of the Hypersonic Wind Tunnel at Sandia National Laboratories. Overall good agreement of the velocity and temperature profiles is obtained with reference data from a direct numerical simulation and a theoretical relationship. Profiles of the resolved root-mean-square velocity fluctuations are in adequate agreement with the reference data. The refractive index is calculated from the density field and integrated along an expected beam path to calculate the optical path length. Then, by subtracting a bilinear fit of the instantaneous optical path length, the optical path difference is obtained. The computed aero-optical path difference shows a similar dependence on the aperture size as in the literature. The normalized root-mean-square optical path difference from the present wall-modeled large-eddy simulations and a reference direct numerical simulation and experiment are in good agreement. The optical path distortion is slightly above the value predicted by a semi-analytical relationship from the literature. Finally, instantaneous snapshots of the flow are analyzed via proper orthogonal decomposition and the optical path distortion is computed from subsets of the modes. The optical path distortion converges quickly with increasing number of modes which suggests that the main contribution comes from large energetic flow structures.