DBPapers
DOI:10.5593/SGEM2013/BC3/S12.054

VELOCITY DISTRIBUTION IN NON-UNIFORM/UNSTEADY FLOWS AND THE VALIDITY OF LOG LAW

I. Alfadhli, Sh.Q. Yang, M. Sivakumar
Monday 5 August 2013 by Libadmin2013

References: 13th SGEM GeoConference on Water Resources. Forest, Marine And Ocean Ecosystems, www.sgem.org, SGEM2013 Conference Proceedings, ISBN 978-619-7105-02-5 / ISSN 1314-2704, June 16-22, 2013, 425 - 432 pp

ABSTRAC

This study investigates the longitudinal velocity profiles in steady and unsteady nonuniform
open channel flows by analyzing the data available in the literature. It was found
that for steady/unsteady flow the Log law is applicable only in the inner region where
y / h  0.2 when compared with the measured longitudinal velocity. However, in the main
flow, the measured velocity deviates significantly from the Log law’s prediction. The detail
assessment shows that the deviation is negative when a flow is accelerating, and positive
when decelerating. The reason for this deviation is explained by linking these deviations
with the presence of wall–normal velocity. A new equation was developed to express the
velocity in non-uniform flow which is valid for uniform flows (Log law) and accelerating
and decelerating steady/unsteady flows, in which Log law, Cole’s Wake law and Dip law
have been combined together to reflect the influence of acceleration on the velocity profile.
This modification has been verified with experimental data sets available in the literature,
and a reasonable agreement between the measured and predicted mean velocity profile is
obtained.

Keywords: uniform/non-uniform flows; velocity distribution; Log-Wake–Dip law;
steady/unsteady flows; accelerating/decelerating flows.