Population trends of spanwise vortices in wall turbulence

Wu, Yanhua; Christensen, Kenneth T.

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https://hdl.handle.net/2142/1711 Copy

Description

Title

Population trends of spanwise vortices in wall turbulence

Author(s)

• Wu, Yanhua
• Christensen, Kenneth T.

Issue Date

2006

Keyword(s)

• Wall turbulence
• Vortices

Date of Ingest

2007-07-24T13:35:54Z

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 Reτ ≡ u∗δ/ν = 570, 1185 and 1760 and a zero-pressure-gradient turbulent boundary layer at Reτ = 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. Appropriate Reynolds-number scalings for outer- and inner-scaled population densities of prograde and retrograde vortices are determined. However, the Reτ = 570 channel-flow case deviates from these scalings, indicating that it suffers from low-Re effects. When the population densities are recast in terms of fractions of resolved prograde and retrograde spanwise vortices, similarity is observed for 100

Publisher

Cambridge University Press

Type of Resource

text

Genre of Resource

Article

Language

en

Permalink

http://hdl.handle.net/2142/1711

DOI

https://doi.org/10.1017/S002211200600259X

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Copyright owned by Cambridge University Press 2006.

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