An experimental study was undertaken to investigate the effects of roughness on the structure of turbulent boundary layers in open channels. The study was carried out using a laser Doppler anemometer in shallow flows for three different types of rough surface, as well as a hydraulically smooth surface. The flow Reynolds number based on the boundary layer momentum thickness ranged from 1400 to 4000. The boundary layer thickness was comparable with the depth of flow and the turbulence intensity in the channel flow varied from 2 to 4 percent. The defect profile was correlated using an approach which allowed both the skin friction and wake strength to vary. The wake parameter was observed to vary significantly with the type of surface roughness in contradiction to the “wall similarity” hypothesis. Wall roughness also led to higher turbulence levels in the outer region of the boundary layer. The profound effect of surface roughness on the outer region as well as the effect of channel turbulence on the main flow indicates a strong interaction, which must be accounted for in turbulence models. [S0098-2202(00)00803-8]
Rough Wall Turbulent Boundary Layers in Shallow Open Channel Flow
Contributed by the Fluids Engineering Division for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received by the Fluids Engineering Division March 23, 1999; revised manuscript received February 14, 2000. Associate Technical Editor: D. Williams.
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Tachie, M. F., Bergstrom, D. J., and Balachandar, R. (February 14, 2000). "Rough Wall Turbulent Boundary Layers in Shallow Open Channel Flow ." ASME. J. Fluids Eng. September 2000; 122(3): 533–541. https://doi.org/10.1115/1.1287267
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