超音速境界層遷移の熱線計測(境界層・せん断流・遷移(2),一般講演)

概要

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To obtain a better understanding of the supersonic boundary layer transition, Pitot-tube and hot-wire measurements are made for a Mach 2 boundary layer along the nozzle wall of a small supersonic wind tunnel. The y-profiles of rms mass flux fluctuations from hot-wire surveys show that the initial stages of the transition are governed by the low-speed streaks caused by streamwise vortices, whose diameters are of the order of the boundary layer thickness and the final stages are characterized by the streak instabilities which develop the key elements of wall turbulence structures, the streamwise vortices and the low-speed streaks which give rise to the log-law velocity profile. It is found that the friction velocity in the transition and the resulting turbulent region can be estimated by correlating the Van Driest transformed mean velocity from Pitot-tube surveys with the composite profile (for incompressible mean velocity) consisting of Reichardt's inner layer profile and Finley's wake function. With these results we may conclude that the transition examined in this study is the same as the subsonic case initially governed by low-speed streaks and streamwise vortices.
2007-08-06