Spanwise structure and scale growth in turbulent boundary layers

Tomkins, Christopher D.; Adrian, Ronald J.

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https://hdl.handle.net/2142/980 Copy

Description

Title

Spanwise structure and scale growth in turbulent boundary layers

Author(s)

• Tomkins, Christopher D.
• Adrian, Ronald J.

Issue Date

2003

Keyword(s)

Boundary layer turbulence

Abstract

Spanwise structure and growth mechanisms in a turbulent boundary layer are investigated experimentally. PIV measurements are obtained in the streamwise– spanwise (x–z)-plane from the buffer layer to the top of the logarithmic region at Reθ =1015 and 7705. The dominant motions of the flow are shown to be large-scale regions of momentum deficit elongated in the streamwise direction. Throughout the logarithmic layer, the regions are consistently bordered by vortices organized in the streamwise direction, offering strong support for a vortex packet model. Additionally, evidence is presented for the existence and organization of hairpin vortices in the region y+ <60. Statistical evidence is also presented for two important aspects of the vortex packet paradigm: vortex organization in the streamwise direction, and the clear association of the hairpin signature with local minima in streamwise velocity. Several spanwise lengthscales are shown to vary linearly with distance from the wall, revealing self-similar growth of spanwise structure in an average sense. Inspection of the data, however, suggests that individual structures do not grow strictly self-similarly in time. It is proposed that additional scale growth occurs by the merging of vortex packets on an eddy-by-eddy basis via a vortex re-connection mechanism similar to that suggested by Wark & Nagib (1989). The proposed mechanism provides a link between vortex-pairing concepts and the observed coalescence of streaky low-speed regions in the inner layer.

Publisher

Cambridge University Press

Type of Resource

text

Language

en

Permalink

http://hdl.handle.net/2142/980

DOI

https://doi.org/10.1017/S0022112003005251

Has Version(s)

Previously published as TAM Report 1006. http://hdl.handle.net/2142/274.

Copyright and License Information

Copyright owned by Cambridge University Press 2003.

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