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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

DIRECT NUMERICAL SIMULATIONS OF TURBULENT BOUNDARY LAYERS OVER SQUARE-EDGED 2-D AND 3-D ROUGH WALLS

pages 1-6
DOI: 10.1615/TSFP7.650
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SINOPSIS

Direct numerical simulations (DNSs) of spatially developing turbulent boundary layers (TBLs) over two-dimensional (2-D) rod- and three-dimensional (3-D) cube-roughened walls were performed to see the roughness effects on the properties of TBL. The 2-D and 3-D roughness were periodically arranged in the downstream direction with pitches of px/k = 2, 3, 4, 6, 8 and 10 and, for the cube the spanwise spacing is fixed at pz/k = 2 with staggered array, where px and pz are the streamwise and spanwise spacings of the roughness and k is the roughness height. Inspection of the Reynolds stresses showed that except for px/k = 2 and 3 over the 2-D rough walls, the effects of the surface roughness extend to the outer layer over the 2-D and 3-D rough walls and the magnitude of the Reynolds stresses in the outer layer is increased in proportion to px/k. The consistent results were observed in the behavior of wall-normal fluctuations ( νw+ ) on the crest of the roughness suggested by Orlandi & Leonardi (2008), indicating that νw+ might be a suitable parameter to predict the influence of the surface roughness in the outer layer over the square-edged rough walls. However, such results are contrary to the trends of the form drag, roughness function and roughness length against px/k, which showed the maximum values at px/k = 8 and 4 over the 2-D and 3-D rough walls respectively.

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