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Scale interactions in velocity and pressure within a turbulent boundary layer developing over a staggered-cube array

Scale interactions in velocity and pressure within a turbulent boundary layer developing over a staggered-cube array
Scale interactions in velocity and pressure within a turbulent boundary layer developing over a staggered-cube array
We experimentally investigate the surface drag characteristics of a staggered-distributed cube array and its interaction with the turbulent structure of the overlying flow. Instantaneous maps of the pressure field, inferred from in-plane velocity data are used to estimate the forces acting on a target roughness element. Coupled statistics of the force in combination with conditional flow analysis and extended proper orthogonal decomposition (POD) of the pressure field, based on the velocity POD modes, elucidate the relevant mechanisms responsible for surface drag generation. The results show that turbulent motions, at different scales, leave an imprint on the pressure field. Specifically, positive and negative fluctuations are generally associated with flow regions experiencing a local deceleration and acceleration, respectively. Although large-scale motions were found to be the single greatest contributor to the fluctuating pressure field, their direct influence on the surface drag fluctuations appears to be mitigated by the relative size of the considerably smaller roughness obstacles. We hypothesise that a pressure wave induced by the passage of alternating high- and low-momentum regions evenly affects the flow field over a broad region, coupling the forces on the windward and leeward sides of the cube, which, in turn, partially cancel each other out. Uncorrelated, intermediate and small-scale pressure events are thus more important to the overall drag fluctuations. While the direct influence of the large-scale structures on the surface drag may be smaller than expected, the results suggest that they are still significant for the role they play in modulating the small-scale pressure events in the canopy region.
boundary layer structure, flow-structure interactions, turbulent boundary layers
0022-1120
Ferreira, M.A.
bdfedfb9-85f6-4dbb-b031-a977cb8f145d
Ganapathisubramani, B.
5e69099f-2f39-4fdd-8a85-3ac906827052
Ferreira, M.A.
bdfedfb9-85f6-4dbb-b031-a977cb8f145d
Ganapathisubramani, B.
5e69099f-2f39-4fdd-8a85-3ac906827052

Ferreira, M.A. and Ganapathisubramani, B. (2021) Scale interactions in velocity and pressure within a turbulent boundary layer developing over a staggered-cube array. Journal of Fluid Mechanics, 910, [A48]. (doi:10.1017/jfm.2020.999).

Record type: Article

Abstract

We experimentally investigate the surface drag characteristics of a staggered-distributed cube array and its interaction with the turbulent structure of the overlying flow. Instantaneous maps of the pressure field, inferred from in-plane velocity data are used to estimate the forces acting on a target roughness element. Coupled statistics of the force in combination with conditional flow analysis and extended proper orthogonal decomposition (POD) of the pressure field, based on the velocity POD modes, elucidate the relevant mechanisms responsible for surface drag generation. The results show that turbulent motions, at different scales, leave an imprint on the pressure field. Specifically, positive and negative fluctuations are generally associated with flow regions experiencing a local deceleration and acceleration, respectively. Although large-scale motions were found to be the single greatest contributor to the fluctuating pressure field, their direct influence on the surface drag fluctuations appears to be mitigated by the relative size of the considerably smaller roughness obstacles. We hypothesise that a pressure wave induced by the passage of alternating high- and low-momentum regions evenly affects the flow field over a broad region, coupling the forces on the windward and leeward sides of the cube, which, in turn, partially cancel each other out. Uncorrelated, intermediate and small-scale pressure events are thus more important to the overall drag fluctuations. While the direct influence of the large-scale structures on the surface drag may be smaller than expected, the results suggest that they are still significant for the role they play in modulating the small-scale pressure events in the canopy region.

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Scale interactions in velocity and pressure within a turbulent boundary layer developing over a staggered-cube array - Accepted Manuscript
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Accepted/In Press date: 5 November 2020
e-pub ahead of print date: 21 January 2021
Published date: 10 March 2021
Keywords: boundary layer structure, flow-structure interactions, turbulent boundary layers

Identifiers

Local EPrints ID: 446811
URI: http://eprints.soton.ac.uk/id/eprint/446811
ISSN: 0022-1120
PURE UUID: 4f6e4b24-d84e-462e-b86f-b4d952660e91
ORCID for M.A. Ferreira: ORCID iD orcid.org/0000-0002-2428-0284
ORCID for B. Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

Catalogue record

Date deposited: 23 Feb 2021 17:32
Last modified: 26 Nov 2021 05:58

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Author: M.A. Ferreira ORCID iD

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