Author(s)

P. Oshkai, T. Yan & A. Howard

Abstract

Quantitative visualization of acoustically coupled shear layers that are formed due to fully turbulent inflow past a coaxial side branch resonator mounted in a duct is performed using a technique of digital particle image velocimetry. Imaging of the flow structure conducted in conjunction with unsteady pressure measurements leads to patterns of velocity, vorticity, and streamline topology at various phases of the acoustic cycle. Global instantaneous images, as well as time-averaged images, are evaluated to provide insight into the flow physics during tone generation. In particular, the effect of the interaction between two shear layers that form across the coaxial side branches on the acoustic power generation is studied for various resonator geometries. Keywords: flow-acoustic coupling, shear layer interaction, coaxial side branch resonators, acoustic power. 1 Introduction Internal flow past a deep cavity (side branch) mounted in a duct is often characterized by the coupling between the self-sustained oscillations of the separated shear layer that forms across the mouth of the cavity and the resonant acoustic modes of the side branch. This resonant phenomenon, which occurs in many industrial processes involving transport of a fluid through a pipeline and is referred to as flow tone generation, involves high-amplitude pressure pulsations and flow oscillations. Flow tone generation past multiple side branches has been a subject of many investigations, as summarized by Ziada and Bühlmann [1]. Classification of side branch resonances as fluid-resonant oscillations was performed by Rockwell and Naudascher [2]. Generally speaking, if the frequency of the shear layer

Keywords

flow-acoustic coupling, shear layer interaction, coaxial side branch resonators, acoustic power.