Predicting the vortex shedding frequency at the interface of the lateral cavities

Clément Perrot-Minot,Emmanuel Mignot,Richard Perkins,Nicolas Riviere,A Paquier,N Rivière

doi:10.1051/e3sconf/20184005011

Abstract

The vortex shedding frequency in the mixing layer between a cavity and a main stream has been examined experimentally in absence of large oscillation of the free surface inside the cavity, called seiching. It was observed that the vortex shedding frequency follows a monotonically increasing trends with possible jumps from one to another with increasing Froude number of the main stream. These trends are obtained by solving a model based on the Rossiter approach. This model considers that the vortices shed in the mixing layer create some water depth variation at the impingement corner of the cavity. This water depth variation in turn generate pressure waves that propagates upstream and influence the vortex shedding process. Finally the measured vortex shedding frequencies correspond quite accurately to the frequencies predicted by the model. This highlights the existence of a resonant phenomena between vortices in the mixing layer of a lateral cavity and gravity waves even without any seiching phenomena.

Highlights

In both hydrology and acoustic fields, cavities are often encountered for industrial and environmental applications
The behaviour of a mixing layer in a lateral cavity with free surface has been studied via velocity measurement
It has been observed that the vortex shedding frequency could only take discrete values for a given Froude number

Summary

Introduction

In both hydrology and acoustic fields, cavities are often encountered for industrial and environmental applications. The large velocity gradient at the interface between the cavity and the main stream produces a mixing layer within which are observed spatially developing vortices. The impact of these vortices on the downstream corner, after their advection along the mixing layer, induces waves that can trigger one dominant mode of the cavity. The flow velocity is high enough for the vortices to generate frequencies matching with the frequency of acoustic waves travelling within the cavity. The velocity is smaller, and vortices can generate oscillation frequencies matching with the frequency of gravity waves travelling at the free-surface of the cavity. A resonant phenomena, called seiching, is likely to appear for specific hydrodynamic and geometric condition, inducing large free surface oscillation inside the cavity [3, 4]

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