University of Illinois Urbana-Champaign

Properties of mean wake recirculation region in two-dimensional bluff body wakes

Balachandar, S.; Mittal, Rajat; Najjar, Fady M.

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https://hdl.handle.net/2142/112540

Description

Title
Properties of mean wake recirculation region in two-dimensional bluff body wakes
Author(s)
  • Balachandar, S.
  • Mittal, Rajat
  • Najjar, Fady M.
Issue Date
1996-12
Keyword(s)
  • Mean Wake Recirculation Region
  • Two-dimensional Bluff Body
Abstract
The properties of the time- and span-averaged mean wake recirculation region are investigated in separated flows over several different two-dimensional bluff bodies. Ten different cases are considered and they divide into two groups: cylindrical geometries of circular, elliptic & square cross-section and the normal plate. A wide Reynolds number range from 250 to 140000 is considered, but in all the cases the attached portion of the boundary layer remains laminar until separation. The lower Reynolds number data are from direct numerical simulations, while the data at the higher Reynolds number are obtained from large eddy simu lation and the experimental work of Cantwell & Coles ( 1983), Krothapalli ( 1996), Leder (1991) and Lyn et al. (1994). Unlike supersonic and subsonic separations with a splitter plate in the wake, in all the cases considered here, there is strong interaction between the shear layers resulting in Karman vortex shedding. Impact of this fundamental difference on the distribution of Reynolds stress components and pressure in relation to the mean wake recirculation region (wake bubble) is considered. It is observed that in all cases the contribution from Reynolds normal-stress to force balance of the wake bubble is significant. In fact, in the cylinder geometries this contribution can outweigh the net force from the shear-stress, so that the net pressure force tends to push the bubble away from the body. In contrast, in the case of normal plate, owing to the longer wake, the net contribution from shear-stress outweighs that from the normal-stress. At higher Reynolds numbers, separation of the Reynolds stress components into coherent and incoherent contributions provides more insight. The behavior of the coherent contribution, arising from the dominant vortex shedding, is similar to that at lower Reynolds numbers. The incoherent contribution to Reynolds stress, arising from small scale activity is compared with that of a canonical free shear layer. Based on these observations a simple extension of the wake model (Sychev 1982 and Roshko 1993a, 1993b) is proposed.
Publisher
Department of Theoretical and Applied Mechanics. College of Engineering. University of Illinois at Urbana-Champaign
Series/Report Name or Number
  • TAM R 838
  • 1996-6025
ISSN
0073-5264
Type of Resource
text
Language
eng
Permalink
http://hdl.handle.net/2142/112540
Copyright and License Information
Copyright 1996 Board of Trustees of the University of Illinois

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