Study on stability of organized horizontal vortices and sediment transport in compound open channel flow

点击翻译按钮获取中文摘要

It has been known that shear instability generates large horizontal vortices at the junctions of main channel and flood plains in two-stage channel. A series of laboratory tests were performed by varying the main channel width, and the tests were conducted for 3 cases of water depth. Fluid velocity and water surface elevation were measured by using laser-Doppler velocimetry and capacity-type wave gage, respectively. It was found that two arrays of vortex streets become very stable at b/H=5, in which b is main channel width and H is main channel depth. The Reynolds stress at the junction shows a peak value at b/H=5 for all cases of water depth. The wavelength of vortices was predicted successfully in terms of linear instability analysis.A series of laboratory tests were also performed in open channel flows with bank vegetation, in which the flow fields become more 2-dimensional than compound open channel flow. Similarly in compound open channel flow, when the vortex streets becomes stable staggered array, the Reynolds stress takes a peak value. The peak value of Reynolds stress is larger than that of compound open channel flow. A numerical computation employing SDS and 2DH turbulence model originally proposed by Nadaoka and Yagi was performed to calculate the 2-dimanesional flow field, supporting the measurements.