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research-article

Measurement of the Excitation Source of an Axisymmetric Shallow Cavity Shear Layer

[+] Author and Article Information
S. Mohamed

Research Assistant Department of Mechanical Engineering, McMaster University, Hamilton, Ontario, Canada
tahasr@mcmaster.ca

H. R. Graf

PROSE AG Winterthur, Switzerland
hansrudolfgraf@bluewin.ch

S. Ziada

Professor Department of Mechanical Engineering, McMaster University, Hamilton, Ontario, Canada
ziadas@mcmaster.ca

1Corresponding author.

ASME doi:10.1115/1.4039781 History: Received November 16, 2017; Revised March 20, 2018

Abstract

The interaction of a cavity shear layer with the sound field of an acoustic mode can generate an aeroacoustic source which is capable of initiating and sustaining acoustic resonances in the duct housing the cavity. This aeroacoustic source is determined experimentally for an internal axisymmetric cavity exposed to high Reynolds number, fully developed turbulent pipe flow without the need to resolve the details of neither the unsteady flow field nor the flow-sound interaction process at the cavity. The experimental technique, referred to here as the Standing Wave Method (SWM), employs six microphones distributed upstream and downstream of the cavity to evaluate the fluctuating pressure difference generated by the oscillating cavity shear layer in the presence of an externally imposed sound wave. The results of the aeroacoustic source are in good agreement with the concepts of free shear layer instability and the fluid-resonant oscillation behaviour. The accuracy of the measurement technique is evaluated by means of sensitivity tests. In addition, the measured source is used to predict the self-excited acoustic resonance of a shallow cavity in a pipeline. Comparison of the predicted and measured results shows the excellent prediction of the self-excited acoustic resonance, including the resonance frequency, the lock-in velocity range, and the amplitude of the self-generated acoustic resonance.

Copyright (c) 2018 by ASME
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