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Population trends of spanwise vortices in wall turbulence

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Title: Population trends of spanwise vortices in wall turbulence
Author(s): Wu, Yanhua; Christensen, Kenneth T.
Subject(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.
Issue Date: 2006-01
Series/Report: TAM Reports 1083
Genre: ArticleTechnical Report
Type: Text
Language: English
URI: http://hdl.handle.net/2142/185
Publication Status: published or submitted for publication
Peer Reviewed: is peer reviewed
Date Available in IDEALS: 2007-01-15
Is Version Of: Published as: Yanhua Wu and K.T. Christensen. Population trends of spanwise vortices in wall turbulence. Journal of Fluid Mechanics, Vol. 568, 2006, pp.55-76. DOI: 10.1017/S002211200600259X. Copyright 2006 Cambridge University Press.
 

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  • Theoretical and Applied Mechanics (TAM) Technical Reports
    TAM technical reports include manuscripts intended for publication, theses judged to have general interest, notes prepared for short courses, symposia compiled from outstanding undergraduate projects, and reports prepared for research-sponsoring agencies.

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