摘要：

An experimental investigation of the spatial structure of second-made 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 how to nearly turbulent how Simultaneous measurements with tao hot-him probes in the boundary layer comprise the primary data set. The mean boundary layer state arts measured with pitot and total temperature surreys. Correlations were taken with circumferential, streamwise, and vertical probe separations. Preliminary results show that 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%. Streamwise convection velocities for the second mode are between 95 and 100% of the edge velocity and wavelengths are approximately two boundary-layer thicknesses, En agreement with stability theory, The second-made waves retain their identity well into the transition process. Structure angle measurements in the transitional boundary layer reveal that the second-mode waves me more highly inclined toward the wall than coherent structures typically observed in turbulent boundary layers.

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