The dynamics of shearing flow over a cavity— A visual study related to the acoustic impedance of small orifices

Abstract

A flat plate containing a two-dimensional rectangular cut-out was exposed to laminar grazing flow of water and a small oscillatory flow through the orifice of the cavity was applied resulting in a wave-like oscillation of the interface between the fluid at rest inside the cavity and the external flow. The interface was visualized by a thin filament of colour dye and the oscillation was recorded by means of a cine-camera. The experimental results are compared to the predictions of a model which had been developed in order to explain the effect of grazing flow on the acoustic impedance of small orifices.