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Exchange flow between a canopy and open water

Published online by Cambridge University Press:  25 September 2008

MIRMOSADEGH JAMALI ,
XUEYAN ZHANG  and
HEIDI M. NEPF
MIRMOSADEGH JAMALI
Affiliation:
Department of Civil Engineering, Sharif University of Technology, Azadi Avenue, Teheran, Iran
XUEYAN ZHANG
Affiliation:
Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
HEIDI M. NEPF
Affiliation:
Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
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Abstract

This paper theoretically and experimentally investigates the exchange flow due to temperature differences between open water and a canopy of aquatic plants. A numerical model is used to study the interfacial shape, frontal velocity and total volumetric exchange, and their dependence on a dimensionless vegetation drag parameter. The numerical predictions are consistent with the laboratory measurements. There is a short initial period in which the force balance is between buoyancy and inertia, followed by drag-dominated flow for which there is a balance between buoyancy and drag forces. After the initial stage, the gravity current propagating into the canopy takes a triangular shape whereas the current propagating into the open water has almost the classic unobstructed horizontal profile, but with a slowly decreasing depth. Near the edge of the canopy, but in the open region, the flow is found to be critical with a unit internal Froude number. The exchange flow rate and the front speed in the canopy decrease slowly with time whereas the gravity current in the open water has a constant speed. The magnitude of the exchange flow decreases as the canopy drag increases. Empirical equations for the flow properties are presented. A movie is available with the online version of the paper.

JFM classification

Geophysical and Geological Flows: Gravity currents
Type
Papers
Information
Journal of Fluid Mechanics , Volume 611 , 25 September 2008 , pp. 237 - 254
Copyright
Copyright © Cambridge University Press 2008

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Jamali et al. supplementary movie

Movie 1. This animation shows the temporal evolution of lock-exchange flow in a half-canopy, corresponding to figure 5 in the paper. The vegetated area (initially containing cold water) is on the right-hand side, and the open water (initially containing warm water) on the left-hand side. The drag parameter (Cbar) is 13.2.

Download Jamali et al. supplementary movie(Video)
Video 3.6 MB