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Control of Coherent Vortex Shedding from Separated Open Channel Flow.

分离明渠流相干涡旋脱落的控制。

基本信息

批准号：
01850120
负责人：
NAKAGAWA Hiroji
金额：
$ 4.42万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research (B).
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-01850120/
关键词：
Turbulence Separated Flow Open Channel Flow Laser Doppler Anemometer Step Flow Coherent Structure Vortex Kolk-boils

项目摘要

The turbulent structure of the backward-facing step flow, including the reverse flow region, in open-channel flows was investigated by making use of two sets of two-component Laser Doppler anemometers (LDA). The turbulence characteristics and reattachment properties were revealed. The time-averaged reattachment length was dependent on both the Reynolds number and Froude number in open-channel flows. In particular, it should be noted that the reattachment length became smaller in supercritical flows than in subcritical flows. The instantaneous reattachment point moved over a distance of the time averaged reattachment length. This suggested strongly that a coherent structure of the kolk-boil vortex might be generated due to the unsteady and low-frequency motions of the reattachment point.The structures of dynamic pressure and shear stress were analyzed on the basis of the momentum equation. These calculated values coincided well with the experimental values measured by the present LDA sy … More stem. The separated step flow and its recirculation in open-channel flows were similar to that in boundary-layer and duct step flows. But, the former was more complicated than the latter, because the pressure was more relaxed by the existence of the free surface.Next, the spectral analyses of pressure and velocity fluctuations revealed that a coherent low-frequency motion existed near the reattachment of the step. In order to reveal the coherent structures in the separated shear layer of the step flows and also in the downstream of the reattachment point, the space-time correlation measurements of the velocity-pressure and velocity-velocity combinations were conducted by using two sets of the Laser Doppler anemometers and the pressure transducer. Quasi-periodic trains of vortical structure were generated due to the Kelvin-Helmholtz instability in the same manner as in the mixing layer, and they were convected toward the reattachment point. The possibility was discussed that these mixing-layer type coherent vortices might trigger a shedding of the large-scale horseshoe vortex from the reattachment point in open-channel flows. Then, this horseshoe vortex could have developed up to the free surface and become boil vortex, which was observed in actual rivers and estuaries. Less

利用两套双分量激光多普勒测速仪（LDA）对明渠后台阶流（包括回流区）的湍流结构进行了研究。揭示了湍流特性和再附特性。在明渠水流中，时均再附着长度与雷诺数和弗劳德数有关。特别是，应该注意的是，再附着长度变得更小，在超临界流比在亚临界流。瞬时再附着点移动了时间平均再附着长度的距离。从动量方程出发，分析了kolk-boil涡的动压和动剪应力结构。计算值与实验值吻合较好 ...更多信息茎明渠流动中的分离台阶流及其回流与边界层和管道台阶流中的分离台阶流及其回流相似。但是，由于自由表面的存在，压力得到了较大程度的缓和，因此前者比后者更为复杂。其次，对压力和速度脉动的谱分析表明，在台阶的再附着附近存在一种低频相干运动。为了揭示台阶流分离剪切层和再附着点下游的相干结构，利用两套激光多普勒风速仪和压力传感器对速度-压力和速度-速度组合进行了时空相关测量。准周期性的列车产生的旋涡结构由于开尔文-亥姆霍兹不稳定性以相同的方式在混合层中，他们对流的再附着点。讨论了这些混合层型拟序涡触发大尺度马蹄涡从明渠流再附着点脱落的可能性。这种马蹄形涡可以发展到自由表面，并成为沸腾涡，这是在实际的河流和河口观察。少