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Measurements in subsonic and supersonic free jets using a laser velocimeter

Published online by Cambridge University Press:  19 April 2006

Jark C. Lau ,
Philip J. Morris  and
Michael J. Fisher
Jark C. Lau
Affiliation:
Lockheed-Georgia Company, Marietta, Georgia
Philip J. Morris
Affiliation:
Lockheed-Georgia Company, Marietta, Georgia
Michael J. Fisher
Affiliation:
Institute of Sound and Vibration Research, University of Southampton, England
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Abstract

Velocity measurements in a 51 mm diameter turbulent jet are presented. The measurement programme is conducted in two parts. The first part is devoted to the validation of laser velocimeter (LV) data. This consists of comparative measurements with the LV and a hot-wire anemometer. The second part consists of a survey of the jet flow field at Mach 0·28, 0·90, and 1·37 under ambient temperature conditions. Radial and centre-line distributions of the axial and radial, mean and fluctuating velocities are obtained. The distributions indicate a decrease in the spreading rate of the mixing layer with increasing Mach number and a corresponding lengthening of the potential core. The results further indicate that these two parameters vary with the square of the jet Mach number. Radial distributions collapse when plotted in terms of ση*, where σ = 10.7/(1 - 0.273 MJ2) and η* = (r − r0·5)/x. This is true for distributions in planes located as far downstream as two potential core lengths. The collapsed data of mean velocity can be approximated by a Görtler error function profile: \[ U/U_J = 0.5[1-{\rm erf}(\sigma\eta^{*})]. \] Centre-line distributions at various Mach numbers also collapse if plotted in terms of x/xc, xc being the potential core length. A general equation for the collapsed data of mean velocity is given by: U/UJ = 1 - exp{1.35/(1 - x/xc)}, for the range of Mach numbers 0·3-1·4, where xc = 4.2 + 1.1 MJ2.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 93 , Issue 1 , 12 July 1979 , pp. 1 - 27
Copyright
© 1979 Cambridge University Press

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