Effects of spanwise spacing on large-scale secondary flows in rough-wall turbulent boundary layers
Effects of spanwise spacing on large-scale secondary flows in rough-wall turbulent boundary layers
Large-scale secondary flows can sometimes appear in turbulent boundary layers formed over rough surfaces, creating low- and high-momentum pathways along the surface (Barros & Christensen, J. Fluid Mech., vol. 748, 2014, R1). We investigate experimentally the dependence of these secondary flows on surface/flow conditions by measuring the flows over streamwise strips of roughness with systematically varied spanwise spacing. We find that the large-scale secondary flows are accentuated when the spacing of the roughness elements is roughly proportional to the boundary layer thickness ${\it\delta}$?, and do not appear for cases with finer spacing. Cases with coarser spacing also generate ${\it\delta}$?-scale secondary flows with tertiary flows in the spaces in between. These results show that the ratio of the spanwise length scale of roughness heterogeneity to the boundary layer thickness is a critical parameter for the occurrence of these secondary motions in turbulent boundary layers over rough walls.
boundary layer structure, turbulent boundary layers, turbulent flows
1-12
Vanderwel, Christina
fbc030f0-1822-4c3f-8e90-87f3cd8372bb
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
2 July 2015
Vanderwel, Christina
fbc030f0-1822-4c3f-8e90-87f3cd8372bb
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Vanderwel, Christina and Ganapathisubramani, Bharathram
(2015)
Effects of spanwise spacing on large-scale secondary flows in rough-wall turbulent boundary layers.
Journal of Fluid Mechanics, 774, .
(doi:10.1017/jfm.2015.292).
Abstract
Large-scale secondary flows can sometimes appear in turbulent boundary layers formed over rough surfaces, creating low- and high-momentum pathways along the surface (Barros & Christensen, J. Fluid Mech., vol. 748, 2014, R1). We investigate experimentally the dependence of these secondary flows on surface/flow conditions by measuring the flows over streamwise strips of roughness with systematically varied spanwise spacing. We find that the large-scale secondary flows are accentuated when the spacing of the roughness elements is roughly proportional to the boundary layer thickness ${\it\delta}$?, and do not appear for cases with finer spacing. Cases with coarser spacing also generate ${\it\delta}$?-scale secondary flows with tertiary flows in the spaces in between. These results show that the ratio of the spanwise length scale of roughness heterogeneity to the boundary layer thickness is a critical parameter for the occurrence of these secondary motions in turbulent boundary layers over rough walls.
Text
Vanderwel_JFM2015_eprints.pdf
- Accepted Manuscript
More information
Accepted/In Press date: 19 May 2015
e-pub ahead of print date: May 2015
Published date: 2 July 2015
Keywords:
boundary layer structure, turbulent boundary layers, turbulent flows
Organisations:
Aerodynamics & Flight Mechanics Group
Identifiers
Local EPrints ID: 377569
URI: http://eprints.soton.ac.uk/id/eprint/377569
ISSN: 0022-1120
PURE UUID: 887926f5-3012-4a79-8953-055fc4020996
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Date deposited: 16 Jun 2015 09:55
Last modified: 15 Mar 2024 03:50
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