Flow and Friction over Natural Rough Beds.
WOODS HOLE OCEANOGRAPHIC INSTITUTION MA
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When a boundary layer develops over a bed that is hydrodynamically rough at a length scale or scales larger than the grain size a macrorough bed, as is usually the case where bed forms are present, it is necessary to distinguish among total boundary shear stress and its components, form drag and spatially averaged skin friction. It is known that the mean-velocity field reflects the composite boundary shear stress. Above about one roughness height above the tops of the roughness elements, the velocity does not vary horizontally. Its vertical profile is semilogarithmic and scales with the total friction velocity ut and total roughness length z ot. This region is here called the integrated logarithmic layer ILL. Below the ILL the velocity varies horizontally in response to the irregular boundary this region is called the surface layer. In the first of two sets of experiments reported here, skin-friction measurements were made with an array of flush-mounted hot films at four points on the stoss slope of one of a field of two-dimensional immobile current ripples. In the second set of experiments, the skin-friction vector field was measured around isolated hemispheres, with model sedimentary tails one and four obstacle heights along and without tails.
- Fluid Mechanics