期刊
JOURNAL OF FLUID MECHANICS
卷 668, 期 -, 页码 174-201出版社
CAMBRIDGE UNIV PRESS
DOI: 10.1017/S0022112010004647
关键词
pipe flow boundary layer; turbulent boundary layers
资金
- Engineering and Physical Sciences Research Council, UK [EP/D037166]
- Natural Sciences and Engineering Research Council of Canada [329117/2006]
- EPSRC [EP/D037166/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/D037166/1] Funding Source: researchfish
The streamwise velocity component is studied in fully developed turbulent channel flow for two very rough surfaces and a smooth surface at comparable Reynolds numbers. One rough surface comprises sparse and isotropic grit with a highly non-Gaussian distribution. The other is a uniform mesh consisting of twisted rectangular elements which form a diamond pattern. The mean roughness heights (+/- the standard deviation) are, respectively, about 76(+/- 42) and 145(+/- 150) wall units. The flow is shown to be two-dimensional and fully developed up to the fourth-order moment of velocity. The mean velocity profile over the grit surface exhibits self-similarity (in the form of a logarithmic law) within the limited range of 0.04 <= y/h <= 0.06, but the profile over the mesh surface does not, even though the mean velocity deficit and higher moments (up to the fourth order) all exhibit outer scaling over both surfaces. The distinction between self-similarity and outer similarity is clarified and the importance of the former is explained. The wake strength is shown to increase slightly over the grit surface but decrease over the mesh surface. The latter result is contrary to recent measurements in rough-wall boundary layers. Single- and two-point velocity correlations reveal the presence of large-scale streamwise structures with circulation in the plane orthogonal to the mean velocity. Spanwise correlation length scales are significantly larger than corresponding ones for both internal and external smooth-wall flows.
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