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Manipulation of free shear flows using piezoelectric actuators

Published online by Cambridge University Press:  26 April 2006

John M. Wiltse  and
Ari Glezer
John M. Wiltse
Affiliation:
Department of Aerospace and Mechanical Engineering, The University of Arizona, Tucson, AZ 85721, USA
Ari Glezer
Affiliation:
Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
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Abstract

An air jet emanating from a square conduit having an equivalent diameter of 4.34 cm and a centreline velocity of 4 m/s is forced using four resonantly driven piezoelectric actuators placed along the sides of the square exit. Excitation is effected via amplitude modulation of the resonant carrier waveform. The flow is normally receptive to time–harmonic excitation at the modulating frequency but not at the resonant frequency of the actuators. When the excitation amplitude is high enough, the excitation waveform is demodulated by a nonlinear process that is connected with the formation and coalescence of nominally spanwise vortices in the forced segments of the jet shear layer. As a result, the modulating and carrier wave trains undergo spatial amplification and attenuation, respectively, downstream of the exit plane. Strong instabilities of the jet column are excited when the jet is forced at phase relationships between actuators that correspond (to lowest order) to the azimuthal modes m = 0, ±1, ±2, and −1 of an axisymmetric flow. The streamwise velocity component is measured phase locked to the modulating signal in planes normal to the mean flow. Resonantly driving the actuators with different carrier amplitudes results in a distorted mean flow having a featureless spectrum that can be tailored to provide favourable conditions for the introduction and propagation of desirable low-frequency disturbances.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 249 , April 1993 , pp. 261 - 285
Copyright
© 1993 Cambridge University Press

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