EXPERIMENTAL STUDY ON 3-D STRUCTURE OF COHERENT HORIZONTAL VORTICES IN COMPOUND OPEN-CHANNEL FLOWS BY USING DUAL-LAYER PIV SYSTEM

Abstract

In compound open-channel flows, there are some large-scale horizontal vortices with a vertical axis. Such coherent vortices influence significantly the transverse transport of scalar variables like suspended sediment between the main-channel and floodplains. So, it is very important in hydraulic engineering and river environment to investigate hydrodynamic characteristics of coherent horizontal vortices in compound open-channel flows and thus there are a lot of experimental and numerical studies on these topics. From recent measurements, it isinferred that the horizontal eddies have a 3-D structure of vortex tubes.
However, 3-D structure of horizontal vortices has not yet been revealed in detail. Therefore, in the present study, a new PIV system using dual-layer laser light sheets was developed and instantaneous velocity fields on two laser sheets were measured simultaneously. As a result, 3-D coherent properties of horizontal vortices and their convection mechanism have been investigated experimentally.