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Turbulent separation upstream of a forward-facing step

Turbulent separation upstream of a forward-facing step
Turbulent separation upstream of a forward-facing step
The turbulent flow over a forward-facing step is studied using two-dimensional time-resolved particle image velocimetry. The structure and behaviour of the separation region in front of the step is investigated using conditional averages based on the area of reverse flow present. The relation between the position of the upstream separation and the two-dimensional shape of the separation region is presented. It is shown that when of ‘closed’ form, the separation region can become unstable resulting in the ejection of fluid over the corner of the step. The separation region is shown to grow simultaneously in both the wall-normal and streamwise directions, to a point where the maximum extent of the upstream position of separation is limited by the accompanying transfer of mass over the step corner. The conditional averages are traced backwards in time to identify the average behaviour of the boundary-layer displacement thickness leading up to such events. It is shown that these ejections are preceded by the convection of low-velocity regions from upstream, resulting in a three-dimensional interaction within the separation region. The size of the low-velocity regions, and the time scale at which the separation region fluctuates, is shown to be consistent with the large boundary layer structures observed in the literature. Instances of a highly suppressed separation region are accompanied by a steady increase in velocity in the upstream boundary layer.
boundary layer separation, turbulent boundary layers
0022-1120
284-304
Pearson, D.S.
6bb65bfe-346b-4cae-9afd-d2dd05342607
Goulart, P.J.
50939b66-9531-465f-8e42-08380f55c8f8
Ganapathisubramani, B.
5e69099f-2f39-4fdd-8a85-3ac906827052
Pearson, D.S.
6bb65bfe-346b-4cae-9afd-d2dd05342607
Goulart, P.J.
50939b66-9531-465f-8e42-08380f55c8f8
Ganapathisubramani, B.
5e69099f-2f39-4fdd-8a85-3ac906827052

Pearson, D.S., Goulart, P.J. and Ganapathisubramani, B. (2013) Turbulent separation upstream of a forward-facing step. Journal of Fluid Mechanics, 724, 284-304. (doi:10.1017/jfm.2013.113).

Record type: Article

Abstract

The turbulent flow over a forward-facing step is studied using two-dimensional time-resolved particle image velocimetry. The structure and behaviour of the separation region in front of the step is investigated using conditional averages based on the area of reverse flow present. The relation between the position of the upstream separation and the two-dimensional shape of the separation region is presented. It is shown that when of ‘closed’ form, the separation region can become unstable resulting in the ejection of fluid over the corner of the step. The separation region is shown to grow simultaneously in both the wall-normal and streamwise directions, to a point where the maximum extent of the upstream position of separation is limited by the accompanying transfer of mass over the step corner. The conditional averages are traced backwards in time to identify the average behaviour of the boundary-layer displacement thickness leading up to such events. It is shown that these ejections are preceded by the convection of low-velocity regions from upstream, resulting in a three-dimensional interaction within the separation region. The size of the low-velocity regions, and the time scale at which the separation region fluctuates, is shown to be consistent with the large boundary layer structures observed in the literature. Instances of a highly suppressed separation region are accompanied by a steady increase in velocity in the upstream boundary layer.

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More information

e-pub ahead of print date: 29 April 2013
Published date: June 2013
Keywords: boundary layer separation, turbulent boundary layers
Organisations: Aerodynamics & Flight Mechanics Group

Identifiers

Local EPrints ID: 354993
URI: http://eprints.soton.ac.uk/id/eprint/354993
ISSN: 0022-1120
PURE UUID: 77b1266a-f229-4761-b0c8-7a4e05eaed1f
ORCID for B. Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

Catalogue record

Date deposited: 12 Aug 2013 10:41
Last modified: 09 Nov 2021 03:23

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Contributors

Author: D.S. Pearson
Author: P.J. Goulart

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