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Experiments on the instability waves in a supersonic jet and their acoustic radiation

Published online by Cambridge University Press:  29 March 2006

Dennis K. Mclaughlin ,
Gerald L. Morrison  and
Timothy R. Troutt
Dennis K. Mclaughlin
Affiliation:
Oklahoma State University, Stillwater, Oklahoma
Gerald L. Morrison
Affiliation:
Oklahoma State University, Stillwater, Oklahoma
Timothy R. Troutt
Affiliation:
Oklahoma State University, Stillwater, Oklahoma
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Abstract

An experimental investigation of the instability and the acoustic radiation of the low Reynolds number axisymmetric supersonic jet has been performed. Hot-wire measurements in the flow field and microphone measurements in the acoustic field were obtained from different size jets at Mach numbers of about 2. The Reynolds number ranged from 8000 to 107000, which contrasts with a Reynolds number of 1·3 × 106 for similar jets exhausting into atmospheric pressure.

Hot-wire measurements indicate that the instability process in the perfectly expanded jet consists of numerous discrete frequency modes around a Strouhal number of 0·18. The waves grow almost exponentially and propagate downstream at a supersonic velocity with respect to the surrounding air. Measurements of the wavelength and wave speed of the St = 0·18 oscillation agree closely with Tam's theoretical predictions.

Microphone measurements have shown that the wavelength, wave orientation and frequency of the acoustic radiation generated by the dominant instability agree with the Mach wave concept. The sound pressure levels measured in the low Reynolds number jet extrapolate to values approaching the noise levels measured by other experimenters in high Reynolds number jets. These measurements provide more evidence that the dominant noise generation mechanism in high Reynolds number jets is the large-scale instability.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 69 , Issue 1 , 13 May 1975 , pp. 73 - 95
Copyright
© 1975 Cambridge University Press

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