Jelly, T. O., Ramani, A., Nugroho, B., Hutchins, N. and Busse, A. (2022) Impact of spanwise effective slope upon rough-wall turbulent channel flow. Journal of Fluid Mechanics, 951, A1. (doi: 10.1017/jfm.2022.823)
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Abstract
Whereas streamwise effective slope (ESx) is accepted as a key topographical parameter in the context of rough-wall turbulent flows, the significance of its spanwise counterpart (ESy) remains largely unexplored. Here, the response of turbulent channel flow over irregular, three-dimensional rough walls with systematically varied values of ESy is studied using direct numerical simulation. All simulations were performed at a fixed friction Reynolds number 395, corresponding to a viscous-scaled roughness height k+ ≈ 65.8 (where k is the mean peak-to-valley height). A surface generation algorithm is used to synthesise a set of ten irregular surfaces with specified ESy for three different values of ESx. All surfaces share a common mean peak-to-valley height and are near-Gaussian, which allows this study to focus on the impact of varying ESy, since roughness amplitude, skewness and ESx can be eliminated simultaneously as parameters. Based on an analysis of firstand second-order velocity statistics, as well as turbulence co-spectra and the fractional contribution of pressure and viscous drag, the study shows that ESy can strongly affect the roughness drag penalty – particularly for low-ESx surfaces. A secondary observation is that particular low-ESy surfaces in this study can lead to diminished levels of outer-layer similarity in both mean flow and turbulence statistics, which is attributed to insufficient scale separation between the outer length scale and the in-plane spanwise roughness wavelength.
| Item Type: | Articles |
|---|---|
| Additional Information: | Funding: We gratefully acknowledge support by the United Kingdom Engineering and Physical Sciences Research Council via grant no. EP/P009875/1, and by the Australian Research Council. This work used the Cirrus UK National Tier-2 HPC Service at EPCC (http://www.cirrus.ac.uk) funded by the University of Edinburgh and EPSRC (EP/P020267/1). T.O.J. gratefully acknowledges the financial support of the University of Melbourne Early Career Researcher Award. A.B. gratefully acknowledges support via a Leverhulme Trust Research Fellowship. |
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Busse, Professor Angela |
| Authors: | Jelly, T. O., Ramani, A., Nugroho, B., Hutchins, N., and Busse, A. |
| College/School: | College of Science and Engineering > School of Engineering > Systems Power and Energy |
| Journal Name: | Journal of Fluid Mechanics |
| Publisher: | Cambridge University Press |
| ISSN: | 0022-1120 |
| ISSN (Online): | 1469-7645 |
| Published Online: | 28 October 2022 |
| Copyright Holders: | Copyright © The Author(s) 2022 |
| First Published: | First published in Journal of Fluid Mechanics 951: A1 |
| Publisher Policy: | Reproduced under a Creative Commons License |
| Data DOI: | 10.25392/leicester.data.21324765 |
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