The effects of conditions at open-channel bed or side shape on the two-dimensional water-surface variations

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In this project, investigations based on hydraulic experiments and numerical simulations are performed in order to examine the effects of the conditions at open-channel bed or side shapes on the water surface variation and oscillation.Regarding the channel bed effects, strip roughness boundaries with various spacing are generated at the channel bottom and hydraulic experiments are conducted with a wide range of the Froude number. Image analysis methods based on the PIV technique are used to analyze the two-dimensional velocity field in the vertical cross section. It was made clear that the deformation of water surface becomes more evident as the increase of the Froude number and the change in the water surface variation is closely related to the generation of the large-scale vertical region near the bottom between the strip roughnesses. The numerical simulation with LES is also performed for a relatively small Froude number, with a result that some of the separated vortices generated at a strip roughness ascend up to the water surface as a boil vortex producing positive divergence field at the water surface. The three-dimensional vortex structure is also revealed from the LES analysis.As for the effects of the side channel shape, a rectangular side cavity with various aspect ratios is attached at a straight open-channel and the two-dimensional water surface oscillation is measured using a stereoscopic image analysis system composed of two high speed-video cameras. The measurement results are analyzed with POD technique in order to detect the fundamental feature of the flow. It was made clear that the surface oscillation mode changes drastically with a change in the aspect ratio of the side cavity. In addition, the three-dimensional flow structure at the side cavity is revealed using a LES simulation that takes into account of the change in the water surface level.