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Self-excited oscillations and mixing in a heated round jet

Published online by Cambridge University Press:  26 April 2006

Peter A. Monkewitz ,
Dietrich W. Bechert ,
Bernd Barsikow  and
Bernhard Lehmann
Peter A. Monkewitz
Affiliation:
Department of Mechanical, Aerospace and Nuclear Engineering. University of California, Los Angeles, CA 90024-1597, USA
Dietrich W. Bechert
Affiliation:
DLR, Institut fuer Turbulenzforschung, Mueller-Breslau-Strasse 8, 1000 Berlin 12, West Germany
Bernd Barsikow
Affiliation:
DLR, Institut fuer Turbulenzforschung, Mueller-Breslau-Strasse 8, 1000 Berlin 12, West Germany
Bernhard Lehmann
Affiliation:
DLR, Institut fuer Turbulenzforschung, Mueller-Breslau-Strasse 8, 1000 Berlin 12, West Germany
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Abstract

An axisymmetric hot-air jet discharging into cold ambient air is investigated experimentally. We consider the transitional regime, that is, Reynolds numbers at which the jet is initially laminar. In the first part of the paper it is demonstrated by several different experiments that, for sufficiently low Reynolds number and a ratio of jet exit to ambient density below approximately 0.7, global oscillations of the ‘jet column’ become self-excited, a behaviour which is related to local absolute instability in the potential core region. The onset of the global oscillations is identified as a Hopf bifurcation and two axisymmetric global modes are observed below the critical density ratio. Finally, it is shown that in the (self-excited) limit-cycle regime the spreading of the hot jet is intermittently quite spectacular, with half-angles in excess of 45°. Using flow visualization, this large spreading of low-density jets is related to the generation of strong ‘side jets’ emanating from the jet column.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 213 , April 1990 , pp. 611 - 639
Copyright
© 1990 Cambridge University Press

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