Discrete-roughness transition for hypersonic flight vehicles

The importance of discrete roughness and the correlations developed to predict the onset of boundary-layer transition on hypersonic flight vehicles are discussed. The paper is organized by hypersonic vehicle applications characterized in a general sense by the boundary layer: slender with hypersonic conditions at the edge of the boundary layer, moderately blunt with supersonic, and blunt with subsonic. This paper is intended to be a review of recent discrete-roughness-transition work completed at NASA Langley Research Center in support of agency flight test programs. First, a review is provided of discrete-roughness wind-tunnel data and the resulting correlations that were developed. Then results obtained from flight vehicles (in particular, the recently flown Hyper-X and shuttle missions) are discussed and compared with the ground-based correlations. Based on these comparisons, wind-tunnel-derived roughness criteria are shown to provide a reliable means for predicting transition behavior for flight vehicles.