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The effects of excitation on the coherent and random motion in a plane wall jet

Published online by Cambridge University Press:  26 April 2006

M. D. Zhou ,
C. Heine  and
I. Wygnanski
M. D. Zhou
Affiliation:
Department of Aerospace Engineering, The University of Arizona, AZ 85721, USA
C. Heine
Affiliation:
Department of Aerospace Engineering, The University of Arizona, AZ 85721, USA
I. Wygnanski
Affiliation:
Department of Aerospace Engineering, The University of Arizona, AZ 85721, USA
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Abstract

Three components of velocity fluctuations were measured in a plane turbulent wall jet which was modulated periodically by a sinusoidal pressure fluctuation in its settling chamber. The experiment was carried out in a closed-loop wind tunnel in the absence of an external stream at Reynolds number Rej = Ujb/v = 6900 and Strouhal number Stj = fb/Uj = 9.5 × 10−3, where b is the width of the slot from which the jet emerges at an efflux velocity Uj. A detailed comparison is provided with similar measurements made in a natural, unexcited turbulent wall jet. One of the purposes of this experiment was to establish the kinetic energy transfers which take place in the wall jet under controlled perturbations. More specifically, we were interested in determining the interactions occurring between the steady mean flow, the coherent eddies and the ‘random’ turbulent fluctuations. We used the triple decomposition of the equations of motion as suggested by Hussain (1983) and quickly observed that the usefulness of this decomposition depends on the definition of coherent motion, which is ambiguous in the presence of phase jitter. Two such definitions were considered and the results are discussed in the experimental case-study provided. An attempt is made to define quantitatively the intensities of the coherent motion in externally excited, wallbounded flows. It is a case-study and not a parametric investigation aimed at maximizing the effects of period oscillations on the wall jet.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 310 , 10 March 1996 , pp. 1 - 37
Copyright
© 1996 Cambridge University Press

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