Hexcomb-Pattern Roughness Effects on Blunt-Body Transition and Heating

Abstract

An experimental investigation of hexcomb-pattern surface roughness effects on boundary-layer transition and convective heating has been performed. Two representative entry vehicle geometries, a spherical-cap aeroshell and a sphere-cone aeroshell, were considered. Multiple cast ceramic models of each geometry were fabricated with various roughness pattern densities and depths that simulated an ablated hexcomb-structure thermal protection system. Wind-tunnel testing was performed at Mach 6 over a range of Reynolds numbers sufficient to produce laminar, transitional, and turbulent flow. Aeroheating and boundary-layer transition onset data were obtained using global phosphor thermography. The experimental heating data are presented herein, as are comparisons to laminar and turbulent smooth-wall heat transfer distributions from computational flowfield simulations. The experimental data were used to develop a unified boundary-layer transition correlation for both sand-grain distributed roughness and hexcomb-pattern roughness.