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Self-excited jet: upstream modulation and multiple frequencies

Published online by Cambridge University Press:  20 April 2006

Michael Lucas  and
Donald Rockwell
Michael Lucas
Affiliation:
Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, Pennsylvania 18015
Donald Rockwell
Affiliation:
Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, Pennsylvania 18015
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Abstract

The self-excited oscillation of a planar jet impinging upon a wedge can give rise to not simply a single, but as many as seven well-defined frequency components in the range of Reynolds-number (based on nozzle width and mean velocity) 250 ≤ Re ≤ 1150. All of these components are traceable to the nonlinear distortion/interaction (i.e. sum and difference) frequencies of two primary components: the most stable frequency of the jet shear layer (β); and a low-frequency modulating component ($\frac{1}{3}$β).

The modulating component $\frac{1}{3}$β arises from vortex-vortex interaction at the impingement edge. This interaction involves vortices of both like and opposite sense; the vortices of opposite sense to those of the incident shear layer arise from eruption of the viscous layer at the edge and tend to form counter-rotating vortex pairs with the incident vortices. The details of the vortex-vortex interaction pattern vary with Reynolds number; however, the pattern adjusts itself to maintain the modulating component $\frac{1}{3}$β. Its upstream influence strongly modulates the sensitive region of the shear layer at the jet nozzle lip. Consequently, the linear-growth region of the disturbance near the lip is dominated by the component $\frac{1}{3}$β, which eventually gives way to the most unstable component β further downstream.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 147 , October 1984 , pp. 333 - 352
Copyright
© 1984 Cambridge University Press

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