An experimental study was conducted to investigate the effect of particle size on the critical velocity and near wall turbulence characteristics of water flow over the sand bed deposited in a horizontal pipeline. Industrial sands of four mesh sizes (20/40, 30/50, 40/70, 100) were used in the study. The particle image velocimetry (PIV) technique was used to determine instantaneous local velocity distribution near the stationary sand bed-fluid interface under flow conditions. The results indicated that the critical velocity for the onset of particle removal from the sand bed as well as the near wall velocity profile, Reynolds shear stress, axial and radial turbulent intensities were all influenced by the variation in particle size range.

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