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Turbulence memory in self-preserving wakes

Published online by Cambridge University Press:  19 April 2006

Paul M. Bevilaqua  and
Paul S. Lykoudis
Paul M. Bevilaqua
Affiliation:
School of Aeronautics, Astronautics and Engineering Sciences, Purdue University, West Lafayette, Indiana 47907 Present address: Rockwell International, Columbus Aircraft Division, Columbus, Ohio 43216.
Paul S. Lykoudis
Affiliation:
School of Aeronautics, Astronautics and Engineering Sciences, Purdue University, West Lafayette, Indiana 47907 Present address: School of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907.
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Abstract

The persistence of the large vortices formed at the origin of wakes and mixing layers constitutes a kind of memory of initial conditions by the turbulence. In order to study the fading of this turbulence memory, and its effect on the rate of approach to the fully developed state, two wakes with different initial conditions have been examined experimentally. The wake of a sphere was compared with the wake of a porous disk which had the same drag, but did not exhibit vortex shedding. Measurements were made of the mean and fluctuating velocities, the anisotropy of the turbulence, and the intermittency. It was found that the wake of the sphere developed self-preserving behaviour more rapidly than the wake of the disk, and that even after both wakes became self-preserving there were differences between them in the structure of the turbulence and the scale of the mean flow. From this it is concluded that the behaviour of self-preserving wakes does not depend on the drag alone, but also on the structure of the dominant eddies. Generalizing these results, it is suggested that reported differences in the value of the entrainment constant of jets, wakes, and mixing layers are due to differences in the structure of the dominant eddies, rather than differences in the type of flow.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 89 , Issue 3 , 13 December 1978 , pp. 589 - 606
Copyright
© 1978 Cambridge University Press

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