Reynolds number dependence of Reynolds and dispersive stresses in turbulent channel flow past irregular near-Gaussian roughness

Jelly, T. O. and Busse, A. (2019) Reynolds number dependence of Reynolds and dispersive stresses in turbulent channel flow past irregular near-Gaussian roughness. International Journal of Heat and Fluid Flow, 80, 108485. (doi: 10.1016/j.ijheatfluidflow.2019.108485)

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Abstract

Direct numerical simulations of fully-developed turbulent channel flow with irregular rough walls have been performed at four friction Reynolds numbers, namely, 180, 240, 360 and 540, yielding data in both the transitionally- and fully-rough regime. The same roughness topography, which was synthesised with an irregular, isotropic and near-Gaussian height distribution, is used in each simulation. Particular attention is directed towards the wall-normal variation of flow statistics in the near-roughness region and the fluid-occupied region beneath the crests, i.e. within the roughness canopy itself. The goal of this study is twofold. (i) Provide a detailed account of first- and second-order double-averaged velocity statistics (including profiles of mean velocity, dispersive stresses, Reynolds stresses, shear stress gradients and an analysis of the mean force balance) with the overall aim of understanding the relative importance of “form-induced” and “turbulence-induced” quantities as a function of the friction Reynolds number. (ii) Investigate the possibility of predicting the levels of streamwise dispersive stress using a phenomenological closure model. Such an approach has been applied successfully in the context of idealised vegetation canopies (Moltchanov & Shavit, 2013, Water Resour. Res., vol. 49, pp. 8222-8233) and is extended here, for the first time, to an irregular rough surface. Overall, the results reveal that strong levels of dispersive stress occur beneath the roughness crests and, for the highest friction Reynolds number considered in this study, show that the magnitude (and gradient) of these “form-induced” stresses exceed their Reynolds stress counterparts. In addition, this study emphasises that the dominant source of spatial heterogeneity within the irregular roughness canopy are “wake-occupied” regions and that a suitable parameterisation of the wake-occupied area is required to obtain an accurate prediction of streamwise dispersive stress.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Jelly, Mr Thomas and Busse, Dr Angela
Authors: Jelly, T. O., and Busse, A.
College/School:College of Science and Engineering > School of Engineering
College of Science and Engineering > School of Engineering > Aerospace Sciences
Journal Name:International Journal of Heat and Fluid Flow
Publisher:Elsevier
ISSN:0142-727X
ISSN (Online):1879-2278
Published Online:28 October 2019
Copyright Holders:Copyright © 2020 The Authors
First Published:First published in International Journal of Heat and Fluid Flow 80:108485
Publisher Policy:Reproduced under a Creative Commons Licence

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
173479Fluid dynamic properties of irregular, multi-scale rough surfacesAngela BusseEngineering and Physical Sciences Research Council (EPSRC)EP/P004687/1ENG - Aerospace Sciences
173614Surface-specific Moody diagram: A new paradigm to predict drag penalty of realistic rough surfaces with applications to maritime transportAngela BusseEngineering and Physical Sciences Research Council (EPSRC)EP/P009875/1ENG - Aerospace Sciences