Space-time correlation measurements in a hypersonic transitional boundary layer

An experimental investigation of the spatial structure of second-mode instability waves was carried out in the boundary layer of a 7-deg half-angle, sharp-nosed cone at an edge Mach number of 6.8. Measurements were made at Reynolds numbers of 2.3 x 10 6 to 9.1 x 10 6 based on boundary edge conditions, spanning the range from unstable laminar flow to nearly turbulent flow. Simultaneous measurements with two hot-film probes in the boundary layer comprise the primary data set. The mean boundary-layer state was measured with pitot and total temperature surveys. Correlations were taken with circumferential, streamwise, and vertical probe separations. The second-mode waves preceding transition are relatively limited in their circumferential dimension, typically less than four boundary-layer thicknesses, based on a coherence level of 20%.