University of Illinois Urbana-Champaign

Population trends of spanwise vortices in wall turbulence

Wu, Yanhua; Christensen, Kenneth T.

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https://hdl.handle.net/2142/185

Description

Title
Population trends of spanwise vortices in wall turbulence
Author(s)
  • Wu, Yanhua
  • Christensen, Kenneth T.
Issue Date
2006-01
Keyword(s)
  • Boundary layer turbulence
  • Vortices
Abstract
The present effort documents the population trends of prograde and retrograde spanwise vortex cores in wall turbulence outside the buffer layer. Large ensembles of instantaneous velocity fields are acquired by particle-image velocimetry in the streamwise{wall-normal plane of both turbulent channel flow at Ret = 570, 1185 and 1760 and a zero-pressure-gradient turbulent boundary layer at Ret = 1400, 2350 and 3450. Substantial numbers of prograde spanwise vortices are found to populate the inner boundary of the log layer of both flows and most of these vortices have structural signatures consistent with the heads of hairpin vortices. In contrast, retrograde vortices are most prominent at the outer edge of the log layer, often nesting near clusters of prograde vortices. Resolved prograde population densities display Ret3/2 dependence in the region 100 < y+ < 0.5d+ while their retrograde counterparts display a similar dependence for y < 0.35d, except for the Ret = 570 case. In addition, similarity in the fractions of resolved prograde and retrograde spanwise vortices is observed for 100 < y+< 0.8d+ in channel flow and in both flows for 100 < y+< 0.3d+ over the Ret range studied. The fraction of retrograde vortices increases slightly with Ret beyond the log layer in both flows, suggesting that they may play an increasingly important role at higher Reynolds numbers. Finally, while the overall prograde and retrograde population trends of channel flow and the boundary layer show little difference for y < 0.45d, the retrograde populations differ considerably beyond this point, highlighting the influence of the opposing wall in channel flow.
Series/Report Name or Number
TAM Reports 1083
Type of Resource
text
Language
en
Permalink
http://hdl.handle.net/2142/185

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