Vortical structures in the near wake of tabs with various geometries

A. M. Hamed, A. Pagan-Vazquez, D. Khovalyg, Z. Zhang, L. P. Chamorro

Research output: Contribution to journalArticle

Abstract

The vortical structures and turbulence statistics in the near wake of rectangular, trapezoidal, triangular and ellipsoidal tabs were experimentally studied in a refractive-index-matching channel. The tabs share the same bulk dimensions, including a 17Â mm height, a 28Â mm base width and a inclination angle. Measurements were performed at two Reynolds numbers based on the tab height, (laminar incoming flow) and 13Â 000 (turbulent incoming flow). Three-dimensional, three-component particle image velocimetry (PIV) was used to study the mean flow distribution and dominant large-scale vortices, while complementary high-spatial-resolution planar PIV measurements were used to quantify high-order statistics. Instantaneous three-dimensional fields revealed the coexistence of a coherent counter-rotating vortex pair (CVP) and hairpin structures. The CVP and hairpin vortices (the primary structures) exhibit distinctive characteristics and strength across and tab geometries. The CVP is coherently present in the mean flow field and grows in strength over a significantly longer distance at the low due to the lower turbulence levels and the delayed shedding of the hairpin vortices. These features at the low are associated with the presence of Kelvin-Helmholtz instability that develops over three tab heights downstream of the trailing edge. Moreover, a secondary CVP with an opposite sense of rotation resides below the primary one for the four tabs at the low . The interaction between the hairpin structures and the primary CVP is experimentally measured in three dimensions and shows complex coexistence. Although the CVP undergoes deformation and splitting at times, it maintains its presence and leads to significant mean spanwise and wall-normal flows.

Original languageEnglish (US)
Pages (from-to)167-188
Number of pages22
JournalJournal of Fluid Mechanics
Volume825
DOIs
StatePublished - Aug 25 2017

Fingerprint

near wakes
Vortex flow
vortices
counters
Geometry
geometry
horseshoe vortices
particle image velocimetry
low level turbulence
flow distribution
Velocity measurement
statistics
Turbulence
Kelvin-Helmholtz instability
trailing edges
Higher order statistics
laminar flow
turbulent flow
inclination
Reynolds number

Keywords

  • vortex flows
  • vortex interactions
  • wakes

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Cite this

Vortical structures in the near wake of tabs with various geometries. / Hamed, A. M.; Pagan-Vazquez, A.; Khovalyg, D.; Zhang, Z.; Chamorro, L. P.

In: Journal of Fluid Mechanics, Vol. 825, 25.08.2017, p. 167-188.

Research output: Contribution to journalArticle

Hamed, A. M. ; Pagan-Vazquez, A. ; Khovalyg, D. ; Zhang, Z. ; Chamorro, L. P. / Vortical structures in the near wake of tabs with various geometries. In: Journal of Fluid Mechanics. 2017 ; Vol. 825. pp. 167-188.
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