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Simulations of bypass transition. (English) Zbl 0983.76027
From the summary: We simulate numerically the bypass transition in an initially laminar boundary layer beneath free-stream turbulence. Transition precursors consist of long backward jets contained in the fluctuating \(u\)-velocity field; they flow backwards relative to the local mean velocity. The jets extend into the upper portion of the boundary layer, where they interact with free-stream eddies. In some locations a free-stream perturbation to the jet shear layer develops into a patch of irregular motion – a sort of turbulent spot. The spot spreads longitudinally and laterally, and ultimately merges into the down-stream turbulent boundary layer. Merging spots maintain the upstream edge of the turbulent region. The jets, themselves, are produced by low-frequency components of the free-stream turbulence that penetrate into the laminar boundary layer. Backward jets are component of laminar region streaks. We also describe a method to construct turbulent inflow from Orr-Sommerfeld continuous modes.

MSC:
76F06 Transition to turbulence
76D10 Boundary-layer theory, separation and reattachment, higher-order effects
76M20 Finite difference methods applied to problems in fluid mechanics
76M22 Spectral methods applied to problems in fluid mechanics
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