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

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, R1-1. (doi: 10.1017/jfm.2017.873)

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 (1933 VDI-Forschungsheft, vol. 361), suggesting that the processed grit-blasted surface can serve as a surrogate for his sand-grain 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.

• Item Type: Articles
• Additional Information: This work was supported by EPSRC grant EP/I032576/1. The authors acknowledge the use of the IRIDIS high performance computing facility at the University of Southampton. Compute time on the ARCHER facility (http://www.archer.ac.uk) is also acknowledged through support from the UK Turbulence Consortium under EPSRC grant EP/L000261/1.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Busse, Professor Angela
• Authors: Thakkar, M., Busse, A., and Sandham, N.D.
• College/School: College of Science and Engineering > School of Engineering > Autonomous Systems and Connectivity
• Journal Name: Journal of Fluid Mechanics
• Publisher: Cambridge University Press
• ISSN: 0022-1120
• ISSN (Online): 1469-7645
• Published Online: 28 December 2017
• Copyright Holders: Copyright © 2017 Cambridge University Press
• First Published: First published in Journal of Fluid Mechanics 837:R1-1-R1-11
• Publisher Policy: Reproduced under a Creative Commons License