Swell Flapping : Self-Induced Free Surface Oshillation Caused by a Separated Jet : Experiments in rectangular tank

Abstract

A new type of self-induced free surface oscillation (swell flapping) was discovered in a system with a jet, a free surface and a structure. An upward plane wall jet was injected into a rectangular tank. The jet impinged on the bottom of an Upper-Inner-Structure (UIS), which was set just beneath the free surface and above the jet inlet channel. The jet was separated at the edge of UIS. At a certain jet inlet velocity and UIS depth, the separated jet oscillated, forming a swell of the free surface around UIS. The maximum swell height from the UIS edge increases with increasing jet inlet velocity, independently of the UIS depth. The oscillating period increases in proportion to the swell height and the velocity. There was the phase difference between the free surface oscillation and the jet fluctuation. The time required for swell rising depends on the jet inlet velocity, while that required for swell breaking corresponds to the wave propagation period.