eprintid: 10076698
rev_number: 20
eprint_status: archive
userid: 608
dir: disk0/10/07/66/98
datestamp: 2019-06-26 15:51:44
lastmod: 2021-09-17 22:29:41
status_changed: 2019-06-26 15:51:44
type: article
metadata_visibility: show
creators_name: Nikora, VI
creators_name: Stoesser, T
creators_name: Cameron, SM
creators_name: Stewart, M
creators_name: Papadopoulos, K
creators_name: Ouro, P
creators_name: McSherry, R
creators_name: Zampiron, A
creators_name: Marusic, I
creators_name: Falconer, RA
title: Friction factor decomposition for rough-wall flows: theoretical background and application to open-channel flows
ispublished: pub
divisions: UCL
divisions: B04
divisions: C05
divisions: F44
keywords: hydraulics, turbulent flows, waves/free-surface flows
note: © Cambridge University Press 2019. This is an Open Access article, distributed under the terms of the Creative Commons Attribution
licence (http://creativecommons.org/licenses/by/4.0/).
abstract: A theoretically based relationship for the Darcy–Weisbach friction factor f for rough-bed open-channel flows is derived and discussed. The derivation procedure is based on the double averaging (in time and space) of the Navier–Stokes equation followed by repeated integration across the flow. The obtained relationship explicitly shows that the friction factor can be split into at least five additive components, due to: (i) viscous stress; (ii) turbulent stress; (iii) dispersive stress (which in turn can be subdivided into two parts, due to bed roughness and secondary currents); (iv) flow unsteadiness and non-uniformity; and (v) spatial heterogeneity of fluid stresses in a bed-parallel plane. These constitutive components account for the roughness geometry effect and highlight the significance of the turbulent and dispersive stresses in the near-bed region where their values are largest. To explore the potential of the proposed relationship, an extensive data set has been assembled by employing specially designed large-eddy simulations and laboratory experiments for a wide range of Reynolds numbers. Flows over self-affine rough boundaries, which are representative of natural and man-made surfaces, are considered. The data analysis focuses on the effects of roughness geometry (i.e. spectral slope in the bed elevation spectra), relative submergence of roughness elements and flow and roughness Reynolds numbers, all of which are found to be substantial. It is revealed that at sufficiently high Reynolds numbers the roughness-induced and secondary-currents-induced dispersive stresses may play significant roles in generating bed friction, complementing the dominant turbulent stress contribution.
date: 2019-08-10
date_type: published
official_url: https://doi.org/10.1017/jfm.2019.344
oa_status: green
full_text_type: pub
language: eng
primo: open
primo_central: open_green
article_type_text: Journal Article
verified: verified_manual
elements_id: 1666517
doi: 10.1017/jfm.2019.344
language_elements: English
lyricists_name: Stoesser, Thorsten
lyricists_id: TSTOE28
actors_name: Flynn, Bernadette
actors_id: BFFLY94
actors_role: owner
full_text_status: public
publication: Journal of Fluid Mechanics
volume: 872
pagerange: 626-664
issn: 1469-7645
citation:        Nikora, VI;    Stoesser, T;    Cameron, SM;    Stewart, M;    Papadopoulos, K;    Ouro, P;    McSherry, R;             ... Falconer, RA; + view all <#>        Nikora, VI;  Stoesser, T;  Cameron, SM;  Stewart, M;  Papadopoulos, K;  Ouro, P;  McSherry, R;  Zampiron, A;  Marusic, I;  Falconer, RA;   - view fewer <#>    (2019)    Friction factor decomposition for rough-wall flows: theoretical background and application to open-channel flows.                   Journal of Fluid Mechanics , 872    pp. 626-664.    10.1017/jfm.2019.344 <https://doi.org/10.1017/jfm.2019.344>.       Green open access   
 
document_url: https://discovery.ucl.ac.uk/id/eprint/10076698/7/Stoesser_Friction%20factor%20decomposition%20for%20rough-wall%20flows.%20Theoretical%20background%20and%20application%20to%20open-channel%20flows_VoR.pdf