Numerical and experimental investigations of unsteady separation zone generated at a right-angled confluence

摘要

The mechanism of unsteady turbulent flow structures generated at a river confluence is still not fully understood. Large flood damages, such as local scour, sediment transport or large water level variations, have been reported at confluences. To reduce such flood damages of a river system, including a river confluence, it is important to examine flow structures at confluences in detail. In this paper, we conducted a laboratory experiment and a Large Eddy Simulation (LES) with a Volume of Fluid (VOF) method to investigate unsteady flow structures associated with flow separation at a right-angled confluence. In the LES, high resolution grids were used to resolve eddies to predict flow structures with high accuracy in space and time. To examine unsteadiness of a large separated region, we focused on streamlines of surface and bottom flows. Through visualizing the streamlines and space-time plots of the surface velocity at the separated region, it was found that the size of the separated region periodically fluctuates and the reattachment point is advected in the downstream direction at almost constant velocity.