WATER SURFACE FLUCTUATION AND ITS ADVECTION FEATURE OF TURBULENT FLOW WITH HEMISPHERIC ROUGHNESS ELEMENTS ANALYZED BY LES WITH IMMERSED BOUNDARY METHOD

Abstract

In non-intrusive river flow measurements such as imaging or radar techniques, water surface irregularities in turbulent flow condition is assumed advected with the surface flow. The surface irregularities are usually considered to be induced by turbulence originated from boil vortices generated near the rough bed. However, the relationship between bottom roughness and water surface fluctuation is not well understood so far. Therefore, we conducted experimental and numerical investigations with relatively simple bed roughness composed of hemispheres. Particle tracing velocimetry (PTV) technique is applied in the experiment and the large eddy simulation (LES) with immersed boundary method (IBM) is used in the simulation. It was made clear that the numerical simulation reproduces the water surface fluctuation fairly well and advection speed of surface pattern can represent the surface flow velocity.