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Three-dimensional wave packets and instability waves in free shear layers and their receptivity

Published online by Cambridge University Press:  26 April 2006

Thomas F. Balsa
Thomas F. Balsa
Affiliation:
Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721, USA
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Abstract

In this paper, we study the evolution of strongly three-dimensional disturbances which are generated by a point force in a parallel mixing layer. When the input force is a pulse, a wave packet develops whose wavefronts are approximately parallel to the spanwise direction. This is in sharp contrast to a wave packet in a wall boundary layer for which the wavefronts are strongly curved. On the other hand, when the input disturbance is oscillating harmonically in time, a spatially growing instability wave develops in a downstream wedge of (x, z)-space. The size of this wedge, as a function of excitation frequency and velocity ratio, is determined. The receptivity of the shear layer to pulse-type and harmonic excitation is also studied. It is found that the shear layer is especially sensitive to relatively high-frequency forcing on its centreline.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 201 , April 1989 , pp. 77 - 97
Copyright
© 1989 Cambridge University Press

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