Orientation of Rough Features Impacts Augmentation of Surface Quantities in Hypersonic Flows

In this work, wall-resolved large eddy simulations (LESs) are presented of three roughness geometries of interest experiencing a Mach eight turbulent boundary layer. The rough-wall geometries represent the common ablation-related features of longitudinal grooves, wavy walls, and crosshatching. This paper presents multiple assessments of the relationship between rough geometries and heating via the equivalent sand-grain roughness parameter [Formula: see text]. First, the effects of pattern orientation on wall quantities are described, and it is observed that although longitudinal (spanwise-varying) features do not augment surface quantities, streamwise-varying and crosshatched-type features do. Next, an assessment of current methods is presented by which equivalent sand-grain roughness can be calculated from LES-predicted quantities. Finally, these findings are related to predictions made using the augmented Spalart–Allmaras rough-wall Reynolds-averaged Navier–Stokes turbulence model; and it is determined that this model, relative to LES, insufficiently predicts wall quantities for a single input roughness height. The limitations of the equivalent sand-grain roughness parameter are discussed in regard to capturing surface effects from oriented geometries under these flow conditions, and recommendations are presented for direct computation, provided geometry orientation is considered.