SPACE-TIME CORRELATION-MEASUREMENTS IN A HYPERSONIC TRANSITIONAL BOUNDARY-LAYER

An experimental investigation of the spatial structure of second-made instability waves was carried out in the boundary layer of a 7-deg hal f-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 b oundary edge conditions, spanning the range from unstable laminar how to nearly turbulent how Simultaneous measurements with tao hot-him pro bes in the boundary layer comprise the primary data set. The mean boun dary layer state arts measured with pitot and total temperature surrey s. Correlations were taken with circumferential, streamwise, and verti cal probe separations. Preliminary results show that the second-mode w aves preceding transition are relatively limited in their circumferent ial dimension, typically less than four boundary-layer thicknesses, ba sed on a coherence level of 20%. Streamwise convection velocities for the second mode are between 95 and 100% of the edge velocity and wavel engths are approximately two boundary-layer thicknesses, En agreement with stability theory, The second-made waves retain their identity wel l into the transition process. Structure angle measurements in the tra nsitional boundary layer reveal that the second-mode waves me more hig hly inclined toward the wall than coherent structures typically observ ed in turbulent boundary layers.