Drag, turbulence, and diffusion in flow through emergent vegetation

Nepf, Heidi

doi:10.1029/1998wr900069

Cited by 1,118 publications

(1,170 citation statements)

References 34 publications

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“…The first condition requires a high Reynolds number (not just the existence of the "-5/3" region which can be an artifact), and the second condition requires low turbulence level, Cru/g < 0.10 from my experience. It is unlikely that these two conditions are satisfied in the experiments as the Reynolds numbers were very low, while the ratio Cru/g > 0.10 was high [Nepf, 1999, Figure 9]. The estimates of e are crucial for the paper, and therefore it would be useful for the author to clarify this problem.…”

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confidence: 99%

Comment on “Drag, turbulence, and diffusion in flow through emergent vegetation” by H. M. Nepf

Nikora¹

2000

Water Resources Research

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In a recent paper, Nepf [1999, p. 479] presented a model "... to describe the drag, turbulence, and diffusion for flow through emergent vegetation which for the first time captures the relevant underlying physics .... "The author also presented a set of laboratory and field experiments and claimed that they support the model. Although this paper may be considered as a valuable and stimulating contribution to the quickly developing field of ecohydraulics, it contains a number of points which require clarifications and comments.1. The Nepf model is heavily based on the turbulence energy balance, which includes the wake production term Pw. .g., Figures 7, 8, and 9). The velocity spectrum in Figure 4 clearly shows that the total turbulence energy k t is much larger than the contribution from wakes at scale d, that is, k t >> k. There is a strong low-frequency maximum at •0.1 Hz, which is, most probably, due to shear turbulence, though its origin is not completely clear as Nepf presented insufficient information on background conditions of experimental runs. Such a shape of the spectrum disagrees with the author's interpretation of (4) and (5), as well as with a statement on page 1985

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confidence: 99%

Comment on “Drag, turbulence, and diffusion in flow through emergent vegetation” by H. M. Nepf

Nikora¹

2000

Water Resources Research

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“…[2011] took an applied numerical modeling approach to flow through emergent vegetation, comparing RANS and a coarse LES utilizing wall functions. They showed that RANS modeling is highly dependent on bespoke, empirical parameterization of the closure scheme representing the forcing due to vegetation, highlighting both the importance of experimental work on salient processes [Nepf, 1999;Nepf and Vivoni, 2000] and the need to consider fluvial RANS closures from a fresh perspective, informed by experiment and theory [King et al, 2012]. The multiple relevant length scales (flow depth, stem diameter, plant height, and canopy scales) and the development of turbulence by mean shear and interactions with the canopy, highlight the complexity of the forcing and the possible need to consider alternative means of conceptualizing the physics (see below).…”

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confidence: 99%

Flow resistance in natural, turbulent channel flows: The need for a fluvial fluid mechanics

Keylock

2015

Water Resources Research

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In fluvial environments, feedbacks among flow, bed forms, sediment, and macrophytes result in a complex fluid dynamics. The assumptions underpinning standard tools in hydraulics are commonly violated and alternative approaches must be formulated. I argue that we should question the assumption that classical notions in fluid mechanics provide the foundations for the techniques of the future. Recent work on turbulent dissipation, interscale modulation of the dynamics, intermittency, and the role of complex forcings is discussed. An agenda for future work is proposed that involves improving our characterization of complex forcings and developing better understanding of the behavior of the velocity gradient tensor in complex, fluvial environments. This leads to the formulation of modeling tools relevant to fluvial fluid mechanics, rather than a reliance on methods developed elsewhere. One avenue by which such methods might be developed is suggested based on the stretched spiral vortex as a baseline topology. This would result in a nonequilibrium model for turbulence that has greater potential to capture the dynamics in which we are interested. Although these ideas are raised in the context of a future fluvial fluid mechanics, they are applicable to any situation where turbulent flows are forced in complicated ways.

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“…과거의 연구들을 보면 실험수로 전단면에 걸쳐 정 수 및 침수식생을 배열하고 항력계수를 측정하거나 식생 역내의 확산에 관한 연구가 수행되었다 (Nepf, 1999;Nepf and Vivoni, 2000;Stone and Shen, 2002;Tanino and Nepf, 2008). 침수식생을 통과하는 경우에는 식생높이 부 근에서 비등방성에 의한 강한 와가 발생한다.…”

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Numerical Simulation of Flow Characteristics behind a Circular Patch of Vegetation using a Two-Dimensional Numerical Model

Kim¹,

Park²

2015

Journal of Korea Water Resources Association

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This paper presents numerical simulations of flow around a circular patch of vegetation using a depthaveraged two-dimensional numerical model which is capable of simulating flow structure in vegetated open channel. In order to account for vegetation effect, drag force terms are included in governing equations. Numerical simulations are conducted with various solid volume fractions (SVF). Flow passes through a circular patch and low velocity region, which is called wake region, is formed downstream of the patch. When SVF is larger than 0.08, a recirculation is observed. The location of the recirculation is moved further downstream as SVF decreases. Von-Kármán vortex street is developed beyond the wake region due to interaction between two shear layers induced by a circular patch of vegetation. The vortex is developed as SVF is larger than 0.08, and the location of the vortex is consistent with the maximum of turbulence kinetic energy. The location of the peak of turbulence kinetic energy is moved further downstream as SVF decreases.

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Drag, turbulence, and diffusion in flow through emergent vegetation

Cited by 1,118 publications

References 34 publications

Comment on “Drag, turbulence, and diffusion in flow through emergent vegetation” by H. M. Nepf

Comment on “Drag, turbulence, and diffusion in flow through emergent vegetation” by H. M. Nepf

Flow resistance in natural, turbulent channel flows: The need for a fluvial fluid mechanics

Numerical Simulation of Flow Characteristics behind a Circular Patch of Vegetation using a Two-Dimensional Numerical Model

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