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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

TURBULENT BOUNDARY LAYER STRUCTURE OVER SPARSELY-DISTRIBUTED ROUGHNESS

pages 1-6
DOI: 10.1615/TSFP7.630
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摘要

Experiments were performed on a surface consisting of sparsely-distributed rigid circular cylinder roughness elements to examine the effects of sparseness on turbulence structure. Measurements were made using both two-component LDV and wide-field planar PIV techniques. The mean velocity profile in defect form conforms to outer-layer similarity. The streamwise and wall-normal turbulence intensities appear to exhibit outer-layer similarity for y > 3ks. However, the Reynolds shear stress is consistently higher compared to smooth-wall as well as other rough-wall data. The higher shear stress appear to be linked with strong ejection events that characterise the outer region of the flow. Two-point spatial correlations of both streamwise and wall-normal velocity fluctuations indicate that the turbulent structures in the outer region are coherent over much larger streamwise distances compared to smooth and other rough-wall cases. These results point to the fact that sparseness plays an important role in the outer-layer structure of turbulent boundary layers over rough walls.

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