Exchange flow between open water and floating vegetation

Zhang, Xueyan; Nepf, Heidi

doi:10.1007/s10652-011-9213-4

Cited by 37 publications

(29 citation statements)

References 23 publications

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“…In many situations, there are substantive obstacles to gravity currents, and in these situations, the drag forces that these obstacles impose can dominate both inertial forces and the drag due to the boundaries of the flow domain. Gravity currents may become drag‐dominated where they propagate into partially or fully vegetated channels, which have been simulated in laboratory experiments by arrays of rigid cylindrical obstacles (Hatcher et al ., ; Tanino et al ., ; Zhang & Nepf, , ). Hatcher et al .…”

Section: Introductionmentioning

confidence: 99%

Sediment deposition from turbidity currents in simulated aquatic vegetation canopies

et al. 2017

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A laboratory flume experiment was carried out in which the hydrodynamic and sedimentary behaviour of a turbidity current was measured as it passed through an array of vertical rigid cylinders. The cylinders were intended primarily to simulate aquatic vegetation canopies, but could equally be taken to represent other arrays of obstacles, for example forests or offshore wind turbines. The turbidity currents were generated by mixing naturally sourced, poly‐disperse sediment into a reservoir of water at concentrations from 1·0 to 10·0 g l−1, which was then released into the experimental section of the flume by removing a lock gate. For each initial sediment concentration, runs with obstacle arrays with solid plant fractions of 1·0% and 2·5%, and control cases with no obstacles, were carried out. The progress of the current along the flume was characterized by the array drag term, CDaxc (where CD is the array drag coefficient, at the frontal area of cylinders per unit volume, and xc is the position of the leading edge of the current along the flume). The downward depositional flux of sediment out of the current as it proceeded was measured at 13 traps along the flume. Analysis of these deposits divided them into fine (2·2 to 6·2 μm) and coarse (6·2 to 104 μm) fractions. At the beginning of their development, the gravity currents proceeded in an inertia‐dominated regime until CDaxc = 5. For CDaxc > 5, the current transitioned into a drag‐dominated regime. For both fine and coarse sediment fractions, the rate of sediment deposition tended to decrease gradually with distance from the source in the inertial regime, remained approximately constant at the early drag‐dominated regime, and then rose and peaked at the end of the drag‐dominated stage. This implies that, when passing through arrays of obstacles, the turbidity currents were able to retain sufficient sediment in suspension to maintain their flow until they became significantly influenced by the drag exerted by the obstacles.

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Section: Introductionmentioning

confidence: 99%

Sediment deposition from turbidity currents in simulated aquatic vegetation canopies

et al. 2017

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“…Turbidity currents encounter arrays of screens that favour local sediment deposition (Oehy & Schleiss 2007). Finally, a case of considerable importance for environmental applications is when a gravitationally driven current propagates into a partially or fully vegetated channel (Tanino, Nepf & Kulis 2005;Zhang & Nepf 2011). Such fluid motions are driven by differences in the temperature of water masses associated with different solar heating in emergent and submerged vegetative regions (Coates & Ferris 1994;Chimney, Wenkert & Pietro 2006) or with different concentrations of phytoplankton that alter the penetration of solar radiation through the water column (Edwards, Wright & Platt 2004).…”

Section: Introductionmentioning

confidence: 99%

Lock-exchange gravity currents propagating in a channel containing an array of obstacles

2015

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Large eddy simulation (LES) is used to investigate the evolution of Boussinesq gravity currents propagating through a channel of height H containing a staggered array of identical cylinders of square cross-section and edge length D. The cylinders are positioned with their axes horizontal and perpendicular to the (streamwise) direction along which the lock-exchange flow develops. The effects of the volume fraction of solids, φ, the Reynolds number and geometrical parameters describing the array of obstacles on the structure of the lock-exchange flow, total drag force acting on the gravity current, front velocity and global energy budget are analysed. Simulation results show that the currents rapidly transition to a state in which the extra resistance provided by the cylinders strongly retards the motion and dominates the dissipative processes. A shallow layer model is also formulated and similarity solutions for the motion are found in the regime where the driving buoyancy forces are balanced by the drag arising from the interaction with the cylinders. The numerical simulations and this shallow layer model show that low-Reynolds-number currents transition to a drag-dominated regime in which the resistance is linearly proportional to the flow speed and, consequently, the front velocity, U f , is proportional to t −1/2 , where t is the time measured starting at the gate release time. By contrast, high-Reynolds-number currents, for which the cylinder Reynolds number is sufficiently high that the drag coefficient for most of the cylinders can be considered constant, transition first to a quadratic drag-dominated regime in which the front speed determined from the simulations is given by U f ∼ t −0.25 , before undergoing a subsequent transition to the aforementioned linear drag regime in which U f ∼ t −1/2 . Meanwhile, away from the front, the depth-averaged gravity current velocity is proportional to t −1/3 , a result that is in agreement with the shallow water model. It is suggested that the difference between these two is due to mixing processes, which are shown to be significant in the numerical simulations, especially close to the front of the motion. Direct estimation of the drag coefficient C D from the numerical simulations shows that the combined drag parameter for the porous medium, Γ D = C D φ(H/D)/(1 − φ), is the key dimensionless grouping of variables that determines the speed of propagation of the current within arrays with different C D , φ and D/H.

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“…The surface excess concept was further developed by Chandesris and Jamet [75]. Zhang and Nepf [78] reported experimental and numerical work on the exchange flow between open water and floating vegetation. Jamet and Chandesris [77] showed that the two-domain and discontinuous one-domain approach are equivalent, provided that the latter is interpreted in the sense of distributions.…”

Section: -4 / Vol 135 June 2013mentioning

confidence: 99%

An Historical and Topical Note on Convection in Porous Media

Nield

Кузнецов

2013

Journal of Heat Transfer

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This note deals with three main themes. The first is a discussion of the early literature on convection in porous media. The second is a brief overview of current analytical modeling of single-phase convection in saturated porous media and in composite fluid/ porous-medium domains. The third is a brief discussion of some pertinent recent studies involving nanofluids, cellular porous materials, bidisperse and tridisperse porous media.

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Exchange flow between open water and floating vegetation

Cited by 37 publications

References 23 publications

Sediment deposition from turbidity currents in simulated aquatic vegetation canopies

Sediment deposition from turbidity currents in simulated aquatic vegetation canopies

Lock-exchange gravity currents propagating in a channel containing an array of obstacles

An Historical and Topical Note on Convection in Porous Media

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