Externally generated turbulence by a vertically oscillating grid plate and its impact on sediment transport rate

摘要

The present paper concerns an experimental study of externally generated turbulence and its impact on the bed load sediment transport in an open channel flow. The external turbulence was generated by vertically oscillating a submerged grid, hereafter referred to as turbulence generator, in the flume with a clearance of 11 cm from the bed. Two kinds of experiments were performed; rigid flat-bed and plane sand-bed. One two-dimensional (2-D) LDA was set up to measure the velocity profiles for different values of flow discharge, amplitude and period of oscillations of the turbulence generator. The mean velocities, turbulence intensities, Reynolds shear stress, and their impacts on the rate of sediment transport have been analyzed. The fractional contributions of burst-sweep cycles to the Reynolds shear stress have also been studied. The turbulence generated due to a vertically oscillating-submerged grid is an analogous to the production of turbulence beneath the roller located on the front of broken wave, and the impact thus lies on the sediment transport. The Shields parameter was found to be correlated with the sediment transport rate, and the transport rate as a function of turbulence level is found to increase with turbulence level.