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Topology of fine-scale motions in turbulent channel flow

Published online by Cambridge University Press:  26 April 2006

Hugh M. Blackburn
Affiliation:
Department of Mechanical Engineering, Monash University, Clayton, Vic 3168, Australia Current address: CSIRO, Division of Building, Construction and Engineering, PO Box 56, Highett, Vic 3190, Australia.
Nagi N. Mansour
Affiliation:
NASA Ames Research Center, Mail Stop 202A-1, Moffett Field, CA 94035, USA
Brian J. Cantwell
Affiliation:
Department of Aeronautics and Astronautics, Stanford University, Stanford, CA 94305, USA

Abstract

An investigation of topological features of the velocity gradient field of turbulent channel flow has been carried out using results from a direct numerical simulation for which the Reynolds number based on the channel half-width and the centreline velocity was 7860. Plots of the joint probability density functions of the invariants of the rate of strain and velocity gradient tensors indicated that away from the wall region, the fine-scale motions in the flow have many characteristics in common with a variety of other turbulent and transitional flows: the intermediate principal strain rate tended to be positive at sites of high viscous dissipation of kinetic energy, while the invariants of the velocity gradient tensor showed that a preference existed for stable focus/stretching and unstable node/saddle/saddle topologies. Visualization of regions in the flow with stable focus/stretching topologies revealed arrays of discrete downstream-leaning flow structures which originated near the wall and penetrated into the outer region of the flow. In all regions of the flow, there was a strong preference for the vorticity to be aligned with the intermediate principal strain rate direction, with the effect increasing near the walls in response to boundary conditions.

Information

Type
Research Article
Copyright
© 1996 Cambridge University Press

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