乱流境界層中の乱流特性量に及ぼす粒子粗面の影響

概要

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The effects of surface roughness on turbulence quantities in a turbulent boundary layer in an open channel are experimentally investigated. A smooth wall, fixed-particle wall and free-particle wall are used as wall boundaries Instantaneous streamwise and vertical water velocities in the turbulent boundary layer are simultaneously measured using a laser-Doppler velocimeter (LDV). The results show that the friction velocity on the fixed-particle wall is larger than that on the freeparticle wall for the same particle density and diameter. This may be attributed to the difference in the relative velocity between particles and fluid in the vicinity of the wall. The distributions of the turbulence quantities such as the Reynolds stress, turbulence intensities and spectra normalized by the friction velocity almost coincide with each other, independent of wall types. This supports the similarity between turbulence quantities, proposed by Townsend^<(1)>. The u-v quadrant decomposition technique and the flow visualization by hydrogen microbubbles indicate that for rough particle-walls the sweeps are more dominant than the ejections in the vicinity of the wall in the turbulent boundary layer.
1997-05-25