Journal article

Friction factor decomposition for rough-wall flows: theoretical background and application to open-channel flows

V Nikora, T Stoesser, SM Cameron, M Stewart, K Papadopoulos, P Ouro, R McSherry, A Zampiron, I Marusic, RA Falconer

Journal of Fluid Mechanics | Cambridge University Press (CUP) | Published : 2019


A theoretically based relationship for the Darcy–Weisbach friction factor 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. T..

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University of Melbourne Researchers


Awarded by EPSRC/UK

Awarded by Australian Research Council

Funding Acknowledgements

Financial support was provided by the EPSRC/UK project 'Bed friction in rough-bed free-surface flows: a theoretical framework, roughness regimes, and quantification' (grants EP/K041088/1 and EP/K04116/1). I.M. acknowledges the support of the Australian Research Council (grant FL120100017). The large-eddy simulations were carried out at Cardiff University's high performance computer, which is part of the Supercomputing Wales project. Useful and stimulating discussions with M. Fletcher (Arup), P. Samuels (HR Wallingford), T. Schlicke (Scottish Environment Protection Agency) and J. Wicks (Jacobs) have been instrumental for this project and are gratefully acknowledged. The editor and three reviewers provided insightful comments and helpful suggestions that have been gratefully incorporated in the final version.