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

TL;DR

This paper introduces an ordinary differential equation based on Reynolds-Averaged Navier-Stokes equations to model velocity distribution and the dip-phenomenon in open channel flows, providing semi-analytical solutions and comparing them with experimental data.

Contribution

It presents a novel differential equation and two approximation laws to predict the velocity dip phenomenon, improving accuracy over existing models.

Findings

The dip correction is less effective for small Coles' parameters.

The simple dip-modified-log-wake law offers intermediate accuracy.

The full dip-modified-log-wake law accurately predicts velocity profiles.

Abstract

An ordinary differential equation for velocity distribution in open channel flows is presented based on an analysis of the Reynolds-Averaged Navier-Stokes equations and a log-wake modified eddy viscosity distribution. This proposed equation allows to predict the velocity-dip-phenomenon, i.e. the maximum velocity below the free surface. Two different degrees of approximations are presented, a semi-analytical solution of the proposed ordinary differential equation, i.e. the full dip-modified-log-wake law and a simple dip-modified-log-wake law. Velocity profiles of the two laws and the numerical solution of the ordinary differential equation are compared with experimental data. This study shows that the dip correction is not efficient for a small Coles' parameter, accurate predictions require larger values. The simple dip-modified-log-wake law shows reasonable agreement and seems to be an interesting tool of intermediate accuracy. The full dip-modified-log-wake law, with a parameter for dip-correction obtained from an estimation of dip positions, provides accurate velocity profiles.