HIFiRE-5 Attachment-Line and Crossflow Instability in a Quiet Hypersonic Wind Tunnel

Abstract

Experiments were conducted on the HIFiRE-5 geometry in a quiet Mach-6 wind tunnel with both low and conventional freestream noise levels. The effect of freestream noise on natural transition on the windward surface and roughness-induced transition on the attachment line was investigated. Elevated freestream noise seemed to change the primary transition mechanism on the windward surface. For quiet flow, there appears to be significant stationary crossflow waves. Traveling crossflow waves were also possibly observed coincident with the stationary waves. With noisy flow, neither stationary nor traveling crossflow instabilities were observed. The primary windward transition mechanism with noisy flow remains unknown. Both two-and three-dimensional roughness geometries were tested on the attachment line. As expected, elevated levels of freestream noise served to decrease the critical roughness height for all roughness geometries tested. Three-dimensional roughness elements proved to be the most destabilizing for both noisy and quiet flow. Based on these results, the specified flight roughness tolerance appears to be quite conservative and should prevent early roughness-induced transition.