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Scalar dispersion by coherent structures in uniformly sheared flow generated in a water tunnel

Scalar dispersion by coherent structures in uniformly sheared flow generated in a water tunnel
Scalar dispersion by coherent structures in uniformly sheared flow generated in a water tunnel
In order to investigate the role of coherent structures as mechanisms of scalar dispersion, we studied measurements of a passive scalar plume released in a uniformly sheared turbulent flow generated in a water tunnel. The flow had homogeneous turbulence properties in the measurement domain and contained hairpin vortices similar to those in boundary layers, and so was an ideal test bed to study the effects of coherent structures on turbulent dispersion, free from the effects of inhomogeneities or boundaries. Measurements of the velocity and concentration fields were acquired simultaneously using stereo particle image velocimetry and planar laser-induced fluorescence. We found that dye was preferentially located far away from vortices and was less likely to appear in close proximity to vortices, which is attributed to the high dissipation at the periphery of the vortices. However, we also found that dye was not directly correlated with the uniform momentum zones in the flow, suggesting a more complex relationship exists between these zones, the locations of vortices, and dye transport. Considering scalar flux events rather than simply the presence of dye as our condition of interest, a conditional eddy analysis demonstrated that hairpin vortices are responsible for the large scalar flux events as well as the large Reynolds stress events in the flow. The fact that the Reynolds stress was correlated with the scalar flux further confirmed that coherent structures are dominant mechanisms for scalar transport. Furthermore, we found that the scalar flux vector was preferentially inclined by 155° and ?25° with respect to the streamwise direction, and was thus approximately orthogonal to the planes of the legs of the most common upright and inverted hairpin structures in the flow. These findings demonstrate that coherent structures play an important and intricate role in turbulent diffusion.
passive scalar turbulance, turbulant mixing, homogeneous turbulence
1468-5248
1-18
Vanderwel, Christina
fbc030f0-1822-4c3f-8e90-87f3cd8372bb
Tavoularis, Stavros
9800ff44-e983-4293-a2b1-f29eec90d359
Vanderwel, Christina
fbc030f0-1822-4c3f-8e90-87f3cd8372bb
Tavoularis, Stavros
9800ff44-e983-4293-a2b1-f29eec90d359

Vanderwel, Christina and Tavoularis, Stavros (2016) Scalar dispersion by coherent structures in uniformly sheared flow generated in a water tunnel. Journal of Turbulence, 1-18. (doi:10.1080/14685248.2016.1155713).

Record type: Article

Abstract

In order to investigate the role of coherent structures as mechanisms of scalar dispersion, we studied measurements of a passive scalar plume released in a uniformly sheared turbulent flow generated in a water tunnel. The flow had homogeneous turbulence properties in the measurement domain and contained hairpin vortices similar to those in boundary layers, and so was an ideal test bed to study the effects of coherent structures on turbulent dispersion, free from the effects of inhomogeneities or boundaries. Measurements of the velocity and concentration fields were acquired simultaneously using stereo particle image velocimetry and planar laser-induced fluorescence. We found that dye was preferentially located far away from vortices and was less likely to appear in close proximity to vortices, which is attributed to the high dissipation at the periphery of the vortices. However, we also found that dye was not directly correlated with the uniform momentum zones in the flow, suggesting a more complex relationship exists between these zones, the locations of vortices, and dye transport. Considering scalar flux events rather than simply the presence of dye as our condition of interest, a conditional eddy analysis demonstrated that hairpin vortices are responsible for the large scalar flux events as well as the large Reynolds stress events in the flow. The fact that the Reynolds stress was correlated with the scalar flux further confirmed that coherent structures are dominant mechanisms for scalar transport. Furthermore, we found that the scalar flux vector was preferentially inclined by 155° and ?25° with respect to the streamwise direction, and was thus approximately orthogonal to the planes of the legs of the most common upright and inverted hairpin structures in the flow. These findings demonstrate that coherent structures play an important and intricate role in turbulent diffusion.

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Accepted/In Press date: 13 February 2016
e-pub ahead of print date: 19 April 2016
Keywords: passive scalar turbulance, turbulant mixing, homogeneous turbulence
Organisations: Aerodynamics & Flight Mechanics Group

Identifiers

Local EPrints ID: 393026
URI: http://eprints.soton.ac.uk/id/eprint/393026
ISSN: 1468-5248
PURE UUID: a0c2219e-f1fc-4347-974b-b7ff2bfec154
ORCID for Christina Vanderwel: ORCID iD orcid.org/0000-0002-5114-8377

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Date deposited: 20 Apr 2016 10:08
Last modified: 15 Mar 2024 05:30

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Author: Stavros Tavoularis

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