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

Abstract

In a recent paper published in this journal, Bonakdari et al. (Environ Fluid Mech

An ordinary differential equation for velocity distribution and dip-phenomenon in open channel flows

“…1a), it is assumed that the vertical gradients (d/dy) are dominating, allowing to therefore neglect the horizontal gradients (d/dz) (Yang et al 2004). Since for large values of y the viscous part (νdU/dy) of the shear stress τ/ρ=(ν dU/dy) v u , where ρ is fluid density, is small versus the turbulent part  v u (Absi 2008), Eq.…”

Investigation of Velocity Distribution in Open Channel Flows Based on Conditional Average of Turbulent Structures

“…Thus, to plot the velocity distribution in the entire flow region using the proposed theoretical equation, it was necessary to determine the value of in (30) accurately. The values of and V + in (30) can be easily calculated using (17) and (21), respectively, from a given data set of upflow velocities. We also note that * in (30) is the mean shear stress; that is, * = √ .…”

“…Bonakdari et al [20] also proposed a new formulation of the vertical velocity profile in open channel flows based on an analysis of the Navier-Stoke equations. On the basis of this law and of the suggestions of Absi [21], a new analytical procedure was presented by Pu et al [22].…”

Analytical methods for velocity distribution and dip-phenomenon in narrow open-channel flows

“…For steady uniform open-channel flows, using the continuity equation, the Reynolds-averaged Navier-Stokes (RANS) momentum equation becomes in the streamwise direction x (1) where x, y and z are respectively the streamwise, vertical and lateral directions and U, V and W the three corresponding mean velocities (u, v and w are the turbulent fluctuations), ν the fluid kinematic viscosity, g the gravitational acceleration, and θ is the angle of the channel bed to the horizontal axis [1] [2].…”

“…Comparison of dip-modified log law profiles (Eq. 2)[6] for different values of coefficient α with experimental data; dashed lines: α = 0 log law profile, solid lines: α = 1.3 exp (-Ar/2) proposed by Yang et al[6], dash-dotted lines: α = 0.5; Symbols: measurements[4] for (a) C4, Ar = 4.68 and S = 0.00401, (b) C3, Ar = 4.68 and S = 0.00296.3.2 A simple dip-modified log-wake lawFigure(1) shows that log law profiles (dashed lines) are valid only in the inner region (ξ = y/h < 0.2). In the outer region (ξ > 0.2) log law deviates from experimental data.…”