Relationship between Bursts and Boils in Open-Channel Flows

Abstract

It has been pointed out that there exist coherent vortices near a free surface in rivers from field observations and that these structures have a close relationship with the "bursting phenomena" generated near the wall. The turbulent structure near the free surface greatly depends on the Froude number and the surface-wave fluctuations. Furthermore, it has been pointed out that the coherent structures and the turbulence statistics near the free surface are closely related with each other. In this study, PIV (Particle-Image Velocimetry) was used to measure evolutionary patterns of coherent vortices in the center of channel. The mean bursting period was evaluated then with a laser Doppler anemometer (LDA). In this way, a relationship between the "bursting phenomena" and the "boils (surface renewal eddies)" was investigated intensively as a function of the Froude number.