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Environmental Fluid Mechanics

, Volume 8, Issue 4, pp 389–394 | Cite as

Comments on “turbulent velocity profile in fully-developed open channel flows”

  • Rafik Absi
Original Article

Abstract

In a recent paper published in this journal, Bonakdari et al. (Environ Fluid Mech 8:1–17, 2008) presented a new formulation of the vertical velocity profile in the central portion of steady fully developed turbulent open-channel flows which is based on an analysis of the Navier–Stokes equations. The predicted mean streamwise velocity profiles presented by the authors represent dip phenomenon (maximum velocity below the free surface). The discusser would like to point out some contradictions and an error in the main demonstration. This error appears in the right-hand side term of the main Eq. 22 (Environ Fluid Mech 8:1–17, 2008) in the parameter α. Our corrected demonstration shows that α is equal to \({\frac{ghsin \theta}{u_*^2}}\) and not to \({\frac{gh sin \theta}{u_*^2} - 1}\) as obtained by the authors (Environ Fluid Mech 8:1–17, 2008). The values of α used by the authors are under-estimated by 1, this difference has a significant effect on velocities and therefore will involve a difference between measured and predicted velocity profiles. Finally, the assumption of \({\frac{\partial U}{\partial z} = 0}\) at the free surface is in contradiction with predicted velocity profiles.

Keywords

Free surface flow Velocity profile Eddy viscosity Dip phenomenon Central portion 

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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  1. 1.EBI, Institute Polytechnic St-LouisCergy UniversityCergy-Pontoise CedexFrance

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