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Article

Drag on a Square-Cylinder Array Placed in the Mixing Layer of a Compound Channel

1
CERIS, Instituto Superior Técnico, Universidade de Lisboa, PT-1049-001 Lisboa, Portugal
2
Hydraulics Lab., Department of Civil Engineering, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece
3
Laboratório Nacional de Engenharia Civil, PT-1700-066 Lisboa, Portugal
4
CERIS, PT-1049-001 Lisboa, Portugal
*
Author to whom correspondence should be addressed.
Academic Editor: Renato Morbidelli
Water 2021, 13(22), 3225; https://doi.org/10.3390/w13223225
Received: 20 October 2021 / Revised: 8 November 2021 / Accepted: 11 November 2021 / Published: 14 November 2021
(This article belongs to the Section Hydraulics and Hydrodynamics)
There are no studies specifically aimed at characterizing and quantifying drag forces on finite cylinder arrays in the mixing layer of compound channel flows. Addressing this research gap, the current study is aimed at characterizing experimentally drag forces and drag coefficients on a square-cylinder array placed near the main-channel/floodplain interface, where a mixing layer develops. Testing conditions comprise two values of relative submergence of the floodplain and similar ranges of Froude and bulk Reynolds numbers. Time-averaged hydrodynamic drag forces are calculated from an integral analysis: the Reynolds-averaged integral momentum (RAIM) conservation equations are applied to a control volume to compute the drag force, with all other terms in the RAIM equations directly estimated from velocity or depth measurements. This investigation revealed that, for both tested conditions, the values of the array-averaged drag coefficient are smaller than those of cylinders in tandem or side by side. It is argued that momentum exchanges between the flow in the main channel and the flow in front of the array contributes to reduce the pressure difference on cylinders closer to the interface. The observed drag reduction does not scale with the normalized shear rate or the relative submersion. It is proposed that the value of the drag coefficient is inversely proportional to a Reynolds number based on the velocity difference between the main-channel and the array and on cylinder spacing. View Full-Text
Keywords: drag coefficient; square cylinder array; mixing layer; compound channel drag coefficient; square cylinder array; mixing layer; compound channel
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MDPI and ACS Style

Ferreira, R.M.L.; Gymnopoulos, M.; Prinos, P.; Alves, E.; Ricardo, A.M. Drag on a Square-Cylinder Array Placed in the Mixing Layer of a Compound Channel. Water 2021, 13, 3225. https://doi.org/10.3390/w13223225

AMA Style

Ferreira RML, Gymnopoulos M, Prinos P, Alves E, Ricardo AM. Drag on a Square-Cylinder Array Placed in the Mixing Layer of a Compound Channel. Water. 2021; 13(22):3225. https://doi.org/10.3390/w13223225

Chicago/Turabian Style

Ferreira, Rui M.L., Miltiadis Gymnopoulos, Panayotis Prinos, Elsa Alves, and Ana M. Ricardo. 2021. "Drag on a Square-Cylinder Array Placed in the Mixing Layer of a Compound Channel" Water 13, no. 22: 3225. https://doi.org/10.3390/w13223225

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