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Characterisation of drag and wake properties of canopy patches immersed in turbulent boundary layers

Characterisation of drag and wake properties of canopy patches immersed in turbulent boundary layers
Characterisation of drag and wake properties of canopy patches immersed in turbulent boundary layers
The wakes and the drag forces of canopy patches with different densities, immersed in turbulent boundary layers, are investigated experimentally. The patches are circular (with outer diameter D) and are made of several identical circular cylinders (height, H and diameter, d). The bulk aspect ratio of all the patches (AR = H~D) was fixed at 1 and the patch density (? = Ncd2~D2, also referred to as solidity) is altered by varying the number of cylinders (Nc) in the patch. Drag measurements show that the patch drag coefficient increases with increasing density. However, the drag coefficient of the highest investigated density (? =0.25) is greater than the drag coefficient of a solid patch (i.e. ? = 1, which is a solid cylinder with AR = 1). PIV measurements were carried out along streamwise-wall-normal (x - y) plane along the centreline of patch and in the streamwise-spanwise (x - z) plane at its mid height (i.e. y = H~2). Mean velocity fields show that the porosity of the patch promotes bleeding along all directions. It was observed that bleeding along the vertical/horizontal direction increases/decreases with increasing ?. Furthermore, it was also observed that bleeding along the lateral direction dictates the point of flow separation along the sides of the patch and makes it independent of ?. All these aspects make wakes for porous patches markedly different from their solid counterpart and provide a rational basis to explain the observed trends in the drag coefficient.
0022-1120
1-22
Taddei, Sonia
d24c8712-7423-4f0a-a2df-5dab24f77a36
Ganapathisubramani, Bharath
5e69099f-2f39-4fdd-8a85-3ac906827052
Manes, Costantino
7d9d5123-4d1b-4760-beff-d82fe0bd0acf
Taddei, Sonia
d24c8712-7423-4f0a-a2df-5dab24f77a36
Ganapathisubramani, Bharath
5e69099f-2f39-4fdd-8a85-3ac906827052
Manes, Costantino
7d9d5123-4d1b-4760-beff-d82fe0bd0acf

Taddei, Sonia, Ganapathisubramani, Bharath and Manes, Costantino (2016) Characterisation of drag and wake properties of canopy patches immersed in turbulent boundary layers. Journal of Fluid Mechanics, 1-22. (In Press)

Record type: Article

Abstract

The wakes and the drag forces of canopy patches with different densities, immersed in turbulent boundary layers, are investigated experimentally. The patches are circular (with outer diameter D) and are made of several identical circular cylinders (height, H and diameter, d). The bulk aspect ratio of all the patches (AR = H~D) was fixed at 1 and the patch density (? = Ncd2~D2, also referred to as solidity) is altered by varying the number of cylinders (Nc) in the patch. Drag measurements show that the patch drag coefficient increases with increasing density. However, the drag coefficient of the highest investigated density (? =0.25) is greater than the drag coefficient of a solid patch (i.e. ? = 1, which is a solid cylinder with AR = 1). PIV measurements were carried out along streamwise-wall-normal (x - y) plane along the centreline of patch and in the streamwise-spanwise (x - z) plane at its mid height (i.e. y = H~2). Mean velocity fields show that the porosity of the patch promotes bleeding along all directions. It was observed that bleeding along the vertical/horizontal direction increases/decreases with increasing ?. Furthermore, it was also observed that bleeding along the lateral direction dictates the point of flow separation along the sides of the patch and makes it independent of ?. All these aspects make wakes for porous patches markedly different from their solid counterpart and provide a rational basis to explain the observed trends in the drag coefficient.

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Accepted/In Press date: 3 May 2016
Organisations: Aeronautics, Astronautics & Comp. Eng

Identifiers

Local EPrints ID: 393760
URI: https://eprints.soton.ac.uk/id/eprint/393760
ISSN: 0022-1120
PURE UUID: 61fe46d0-f3e5-4b96-94ab-88643fd2c0af
ORCID for Bharath Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

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Date deposited: 04 May 2016 10:34
Last modified: 06 Jun 2018 12:33

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