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Direct numerical simulation of turbulent channel flow over a surrogate for Nikuradse-type roughness

Direct numerical simulation of turbulent channel flow over a surrogate for Nikuradse-type roughness
Direct numerical simulation of turbulent channel flow over a surrogate for Nikuradse-type roughness
A tiled approach to rough surface simulation is used to explore the full range of roughness Reynolds numbers, from the limiting case of hydrodynamic smoothness up to fully rough conditions. The surface is based on a scan of a standard grit-blasted comparator, subsequently low-pass filtered and made spatially periodic. High roughness Reynolds numbers are obtained by increasing the friction Reynolds number of the direct numerical simulations, whereas low roughness Reynolds numbers are obtained by scaling the surface down and tiling to maintain a constant domain size. In both cases, computational requirements on box size, resolution in wall-units and resolution per minimum wavelength of the rough surface are maintained. The resulting roughness function behaviour replicates to good accuracy the experiments of Nikuradse (VDI-Forschungsheft 361, 1933), suggesting that the processed grit-blasted surface can serve as a surrogate for his sandgrain roughness, the precise structure of which is undocumented. The present simulations also document a monotonic departure from hydrodynamic smooth wall results, which is fitted with a geometric relation, the exponent of which is found to be inconsistent with both the Colebrook formula and an earlier theoretical argument based on low-Reynolds number drag relations.
0022-1120
Thakkar, M.
0c465d92-64b4-4c9e-b34f-4095c89a240f
Busse, A.
0430b320-341b-4c73-9cb5-f35632d562a4
Sandham, N.D.
0024d8cd-c788-4811-a470-57934fbdcf97
Thakkar, M.
0c465d92-64b4-4c9e-b34f-4095c89a240f
Busse, A.
0430b320-341b-4c73-9cb5-f35632d562a4
Sandham, N.D.
0024d8cd-c788-4811-a470-57934fbdcf97

Thakkar, M., Busse, A. and Sandham, N.D. (2018) Direct numerical simulation of turbulent channel flow over a surrogate for Nikuradse-type roughness. Journal of Fluid Mechanics, 837, [R1]. (doi:10.1017/jfm.2017.873).

Record type: Article

Abstract

A tiled approach to rough surface simulation is used to explore the full range of roughness Reynolds numbers, from the limiting case of hydrodynamic smoothness up to fully rough conditions. The surface is based on a scan of a standard grit-blasted comparator, subsequently low-pass filtered and made spatially periodic. High roughness Reynolds numbers are obtained by increasing the friction Reynolds number of the direct numerical simulations, whereas low roughness Reynolds numbers are obtained by scaling the surface down and tiling to maintain a constant domain size. In both cases, computational requirements on box size, resolution in wall-units and resolution per minimum wavelength of the rough surface are maintained. The resulting roughness function behaviour replicates to good accuracy the experiments of Nikuradse (VDI-Forschungsheft 361, 1933), suggesting that the processed grit-blasted surface can serve as a surrogate for his sandgrain roughness, the precise structure of which is undocumented. The present simulations also document a monotonic departure from hydrodynamic smooth wall results, which is fitted with a geometric relation, the exponent of which is found to be inconsistent with both the Colebrook formula and an earlier theoretical argument based on low-Reynolds number drag relations.

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Accepted/In Press date: 24 November 2017
e-pub ahead of print date: 28 December 2017
Published date: 25 February 2018

Identifiers

Local EPrints ID: 415984
URI: http://eprints.soton.ac.uk/id/eprint/415984
ISSN: 0022-1120
PURE UUID: 1be75f81-5bd4-41cd-92d0-c5c08e57a453
ORCID for N.D. Sandham: ORCID iD orcid.org/0000-0002-5107-0944

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Date deposited: 29 Nov 2017 17:30
Last modified: 07 Oct 2020 05:36

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