Very high Reynolds number boundary layers over 3D sparse roughness and obstacles: the mean flow |
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Authors: | A Akomah H Hangan J Naughton |
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Institution: | (1) The Boundary Layer Wind Tunnel Laboratory, The University of Western Ontario, London, ON, Canada;(2) Mechanical Engineering Department, University of Wyoming, Laramie, WY, USA;(3) Present address: Ministry of Transportation, Downsview, ON, Canada; |
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Abstract: | Hot-wire and oil-film interferometry measurements are taken for 3D rough wall boundary layers at very high Reynolds numbers
(61,000 < Re θ < 120,000) with low blockage ratios, 10 < δ/H < 135, and high roughness, 100 < H
+ < 4,900. The results cover flows over both rough walls and over obstacles and are compared with and provide extension to
recent lower Reynolds number results. The validity of the Townsend ‘wall similarity hypothesis’ in relation to consistently
increasing 3D roughness is interrogated. In agreement with recent work, Schultz and Flack (J Fluid Mech 580:381–405, 2007) and Castro (J Fluid Mech 585:469–485, 2007) found that, for relatively low roughness, Townsend’s hypothesis holds for the mean velocity field. With increasing roughness,
the equilibrium layer diminishes and gradually vanishes. The viscous component of the wall shear stress decreases, while the
turbulent component increases as the roughness effects extend across the boundary layer. |
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Keywords: | |
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