On the critical condition for wall turbulence generation
The critical flow condition for self-sustaining wall turbulence and the related minimum Reynolds number are examined on the basis of our previous and new experiments on the subcritical transition in channel and flat-plate flows to obtain a better understanding of the mechanism for wall turbulence generation. It is stressed that energetic hairpin eddies coming from upstream can trigger the subcritical disturbance growth, or their regeneration, in Blasius flow beyond R θ = 110 ~ 130. Downstream, the mean velocity can follow the logarithmic distribution beyond R θ = 210. We also find that the minimum Reynolds number R θ is not much different for the pipe, channel and flat-plate wall flows.
KeywordsSecondary Instability Wall Turbulence Plane Poiseuille Flow Boundary Layer Plate Stagger Cylinder
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