EXPERIMENTAL INVESTIGATION OF ROUGHNESS AND BLOWING EFFECTS OVER ABLATOR-LIKE SURFACES
Two separate experiments using PIV were carried out to investigate the effects of roughness and blowing over surfaces geometrically similar to ablation materials used for atmospheric re-entry. The first, water tunnel experiments, employed a dimpled surface similar to AVCOAT, while the second set was completed in a wind tunnel with a material similar to PICA. For the first set, the flow with blowing becomes destabilized, and more disorganized. The blowing disrupts the relatively simple vorticity
... shedding process and significantly modifies momentum transport via interaction of detached structures. Flow structure and their modifications were examined with a sPOD analysis. The focus of the wind tunnel experiments was to examine the effects of blowing on the mean flow and wall-shear stress measured using an approach derived from the RANS equation. Significant reductions in skin friction are observed, some below that of the smooth wall case. Given experimental limitations, assumptions made in the wall shear stress measurement derivation may not have been met. Despite a reduction in skin friction, an increase in turbulence is observed. The Reynolds stresses reflect this, and counter to Townsend's similarity hypothesis, they indicate scaling that with τw alone is unsuitable for the case of roughness and blowing.