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Seventh International Symposium on Turbulence and Shear Flow Phenomena
July, 28-31, 2011, Ottawa Convention Centre, Ottawa, Canada

DOI: 10.1615/TSFP7

LARGE-EDDY SIMULATION OF ACCELERATING BOUNDARY LAYERS OVER ROUGH SURFACES

pages 1-6
DOI: 10.1615/TSFP7.2010
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ABSTRACT

Large-eddy simulations (LES) are carried out to study the combined effects of roughness and pressure gradient in boundary layer flows, where the high acceleration facilitates flow reversion to the quasi-laminar state. First, validations of the immersed-boundary scheme and the LES resolution are carried out on rough-wall open-channel flows. Then the roughness model is applied to boundary layers subject to strong acceleration, leading to relaminarization and retransition. The roughness (represented by the roughness Reynolds number k+) counteracts with the favourable pressure gradients (FPGs): while flow acceleration tends to stabilize the flow by significantly damping turbulent motions in the vertical and spanwise directions and produces one-dimensional turbulence after the high-acceleration region, the roughness elements increase the turbulent mixing in the wall layer, reducing the stability of the low-speed streaks, and leading to earlier retransition to turbulence.

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