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

1.本文的主要研究内容是：（1）弄清明渠阶跃流中的湍流结构及其由再附着脱落的拟序涡;（2）弄清明渠同向流混合层中的拟序结构，发展混合的湍流控制.明渠阶跃流的湍流结构本文用激光多普勒测速仪研究了分离阶跃流中的湍流结构。得到了流场的平均速度分布和湍流特性。从动量方程出发，分析了压力分布和雷诺应力分布。经验证，瞬时再附着移动的距离高达50%的时间平均再附着长度。再附过程中速度和壁面压力脉动的时空相关性表明，准周期性的涡结构串从再附过程中脱落，然后发展到自由表面，形成沸腾涡.同向流动中的拟序结构与湍流控制的发展在明渠流动中，拟序涡产生于汇合处的混合层中，并通过周围流体的卷吸而聚并，对湍流混合起着重要的作用。本研究利用流动显示和热膜风速仪研究了同向流速度比和外部扰动对相干涡运动的影响。结果表明，低频扰动促进了聚结过程，而高频扰动则抑制了聚结过程。

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.