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Direct numerical simulation of ‘short’ laminar separation bubbles with turbulent reattachment. (English) Zbl 0959.76035
Conclusions: Simulations of short laminar separation bubbles have been carried out in two and three dimensions. The three-dimensional simulations show full transition to turbulence, the process being characterized by breakdown of \(\Lambda\)-vortices. Budgets of turbulence kinetic energy and Reynolds stresses show that the flow just after reattachment consists of an upper region, corresponding quite closely to the upper half of a turbulent mixing layer, and a near-wall portion with a redeveloping turbulent boundary layer. The relaxation towards equilibrium is slow. At least seven bubble lengths are required to reach the usual log law. Stability analysis shows that profiles with more than 15% reverse flow are required for absolute instability, whereas the bubbles simulated have lower levels of reverse flow. Two-dimensional simulations do not appear to represent adequately the characteristics of the short separation bubbles.

MSC:
76F65 Direct numerical and large eddy simulation of turbulence
76F40 Turbulent boundary layers
76D10 Boundary-layer theory, separation and reattachment, higher-order effects
76M22 Spectral methods applied to problems in fluid mechanics
76T10 Liquid-gas two-phase flows, bubbly flows
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