Mean flow scaling along smooth and rough wall boundary layers
E.-S. Zanoun
Keywords: Smooth/rough walls, low Reynolds number, boundary layer flow
Pages: 23-42
Abstract
Effects of the upstream conditions and the degree of the wall roughness on the mean velocity profiles and some integral flow parameters in two dimensional zero-pressure-gradient boundary layer were characterized experimentally. The results were analyzed utilizing conventional and recent scaling flow parameters for 245< Reθ ≤ 11·103, where Reθ is the Reynolds number based on the free stream velocity and the momentum thickness (θ). Good correlation of the quantity as a function of the roughness parameter k+ was obtained for sand roughness of 1.7 < k+ ≤ 172, revealing a universality of the roughness effect, where =
= ( − )/uτ and k+ = kuτ /ν. The mean flow structure of the outer flow was observed not to be influenced by the degree of the wall roughness, i. e., the outer flow of either the smooth or the rough surfaces scales similarly with the various scaling parameters regardless the degree of the wall roughness. However, it made flow confined to the wall region away from the classical universality, allowing similarity hypothesis not to be identical in the wall region at least for the current range of the Reynolds number.
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