Development of Turbulence Control and its Application to Sediment and Mass Transfer

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1. IntroductionThe present main research project is to (1) make clear the turbulent structure in open channel step flows and its coherent eddies shed from the reattachment and (2) make clear the coherent structure in the mixing layer of coflows in open channel and develop the turbulence control of mixing.2. Turbulent structure in open channel step flowThe turbulent structures in the separated step flows were investigated by making use of a Laser Doppler anemometer. The mean velocity distribution and turbulence characteristics were made clear. The pressure distribution and Reynolds stress distribution were analyzed on the basis of momentum equation. It was verified that the instantaneous reattachment moved over the distance of up to 50% of the time-averaged reattachment length. The space-time correlations between the velocity and wall-pressure fluctuations on the reattachment indicated that quasi-periodic trains of vortical structure were shed from the reattachment and then they developed up to the free surface and became boil vortex.3. Coherent structure in coflows and development of turbulence controlThe coherent vortex is generated in the mixing layer of confluence in open channel flows, and then coalesces through entrainment of surrounding fluids, which plays an important role on turbulent mixing. The present study examined the effects of the velocity ratio of coflows and also the external disturbances on the coherent vortex motions, by making use of flow visualization and hot-film anemometers. As the results, the coalescence was promoted in low-frequency disturbances, while it was depressed in high-frequency disturbances.