Development of Wall Turbulence in Blasius Flow
The subcritical transition in Blasius flow is examined experimentally through observing its response to nonlinear disturbanres due to high- intensity hairpin eddies acoustically excited at the leading edge of boundary- layer plate. When disturbed by the leading-edge-generated hairpin eddies, the near wall flow is found to develop local wall shear layers with streamwise vortices. The local three- dimensional shear layers also evolve into hairpin eddies in succession to lead to the subcritical transition for displacement-thickness Reynolds numbers beyond 330. It is also shown that in terms of u- and v- fluctuations, the intensity of the near wall activity at the above-cited critical Reynolds number is almost the same (or slightly less than) that of the developed wall turbulence.
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