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Identification and Analysis of Vortical Structures in a Ribbed Channel

[+] Author Affiliations
Lei Wang, Bengt Sundén

Lund University, Lund, Sweden

Mirko Salewski

Technical University of Denmark, Roskilde, Denmark

Paper No. FEDSM2008-55055, pp. 293-301; 9 pages
doi:10.1115/FEDSM2008-55055
From:
  • ASME 2008 Fluids Engineering Division Summer Meeting collocated with the Heat Transfer, Energy Sustainability, and 3rd Energy Nanotechnology Conferences
  • Volume 1: Symposia, Parts A and B
  • Jacksonville, Florida, USA, August 10–14, 2008
  • Conference Sponsors: Fluids Engineering Division
  • ISBN: 978-0-7918-4840-1 | eISBN: 0-7918-3832-3
  • Copyright © 2008 by ASME

abstract

Vortical motions, usually called sinews and muscles of fluid motions, constitute important features of turbulent flows and form the base for large-scale transport processes. In this study, we present a variety of flow decomposition techniques to identify and analyze the vortical structures in a ribbed channel. To this end, the instantaneous velocity fields are measured by means of a two-dimensional particle image velocimetry (PIV). Firstly, the implementation of Galilean-, Reynolds- and large-eddy simulation (LES) decompositions on the instantaneous flow fields allows one to perceive the coherent vortices embedded in the separated shear layer. In addition, the proper orthogonal decomposition (POD) is employed to extract the underlying flow features out of the fluctuating velocity and vorticity fields, respectively. For velocity-based decomposition, the first two POD modes show that the shear layer is highly unstable and associated with the ‘flapping’ motion. For vorticity-based decomposition, the first two POD modes are characterized by the distinct horizontal bands which manifest the coherent structures in the shear layer. In order to interpret the flow structures in a convenient way, a linear combination of POD modes (reconstruction) is also carried out in the present study. The result shows that a large-scale, pronounced vortex is recognizable in the region downstream of rib.

Copyright © 2008 by ASME

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