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Similarity behaviour of momentumless turbulent wakes

Published online by Cambridge University Press:  29 March 2006

Michael L. Finson
Affiliation:
Avco Everett Research Laboratory, Inc., Everett, Massachusetts 02149 Present address: Physical Sciences Inc., Wakefield, Massachusetts 01880.

Abstract

Similarity solutions are determined for the turbulent wake of a self-propelled body (thrust = drag). The momentumless wake is shown to behave in a manner intermediate to homogeneous grid turbulence and more familiar free-shear flows such as the drag wake or jet. In essence the decay of momentumless-wake turbulence is similar to that of grid turbulence, but proceeds at a somewhat greater rate owing to lateral diffusion. The mean velocity difference is coupled to the difference $\overline{u^2}-\overline{v^2}$ between the axial and radial components of the mean-square fluctuating velocity. It is necessary to consider governing relations for various second-order turbulence quantities. Previously developed closure approximations yield far-wake decay rates that agree well with available measurements. Production of turbulent energy is negligible asymptotically; thus there is no balance between production and dissipation, and the far-wake behaviour does not become independent of the initial (near-wake) conditions. Even the radial profiles depend on the initial conditions, and there is no natural length scale with which to characterize the far wake.

Type
Research Article
Copyright
© 1975 Cambridge University Press

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