A Second-Order Closure for Neutrally Stratified Vegetative Canopy Flows

Ayotte, Keith W.; Finnigan, John; Raupach, Michael

doi:10.1023/a:1001722609229

Cited by 97 publications

(88 citation statements)

References 27 publications

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“…Common approaches use the squared arithmetic mean of the streamlined wind speed ð" u 2 Þ for U 2 . This has the consequence that, deep in the canopy where the mean velocity is low but turbulence levels remain high, the loss of kinetic energy is underestimated (Ayotte et al 1999). An alternative averaging scheme replaces U 2 with the averaged product of the absolute instantaneous wind intensity U j j and instantaneous longitudinal wind component u (see Cescatti and Marcolla 2004).…”

Section: Velocity Scale Umentioning

confidence: 99%

Wind fields in heterogeneous conifer canopies: parameterisation of momentum absorption using high-resolution 3D vegetation scans

et al. 2011

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Applications of flow models to tall plant canopies are limited, amongst other factors, by the lack of detailed information on vegetation structure. A method is presented to record 3D vegetation structure and make this information applicable to the derivation of turbulence parameters suitable for flow models. The relationship between wind speed, drag coefficient (C D ) and plant area density (PAD) was experimentally investigated in a mixed conifer forest in the lower part of the Eastern Ore Mountains. Essential information was gathered by collecting multi-level high-frequency wind velocity measurements and a dense 3D representation of the forest was obtained from terrestrial laser scanner data. Wind speed dependence or streamlining was observed for most of the wind directions. Edge effects, i.e. the influence of the here not regarded pressure gradient and the advective terms of the momentum equation, are assumed to cause this heterogeneity. Contrary to the hypothetic shelter effect, which would reduce the drag on sheltered plant parts, the calculated profiles of drag coefficients revealed an increasing C D with PAD (i.e. a dependence on canopy and plant structure).

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Section: Velocity Scale Umentioning

confidence: 99%

Wind fields in heterogeneous conifer canopies: parameterisation of momentum absorption using high-resolution 3D vegetation scans

et al. 2011

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“…Identifying the minimum turbulence closure model necessary to efficiently simulate the mean flow and measures of second-order flow statistics is a logical research question (Wilson et al, 1998). In principle, second-order closure models can predict such flow statistics (Meyers andPaw U, 1986, 1987;Meyers, 1987;Wilson, 1988;Paw and Meyers, 1989;Albertson, 1998, 1999;Ayotte et al, 1999;Katul and Chang, 1999). However, they are computationally expensive and require complex numerical algorithms for three-dimensional transport problems (especially if multiple scalar species must be treated).…”

Section: Introductionmentioning

confidence: 99%

ONE- and TWO-Equation Models for Canopy Turbulence

Katul

Mahrt

Poggi

et al. 2004

Boundary-Layer Meteorology

338

223

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Abstract. The predictive skills of single-and two-equation (or K-e) models to compute profiles of mean velocity (U), turbulent kinetic energy (K), and Reynolds stresses ðu 0 w 0 Þ are compared against datasets collected in eight vegetation types and in a flume experiment. These datasets range in canopy height h from 0.12 to 23 m, and range in leaf area index (LAI) from 2 to 10 m 2 m À2 . We found that for all datasets and for both closure models, measured and modelled U, K, and u 0 w 0 agree well when the mixing length (l m ) is a priori specified. In fact, the root-mean squared error between measured and modelled U, K, and u 0 w 0 is no worse than published values for second-and third-order closure approaches. Within the context of onedimensional modelling, there is no clear advantage to including a turbulent kinetic dissipation rate (e) budget when l m can be specified instead. The broader implication is that the added complexity introduced by the e budget in K-e models need not translate into improved predictive skills of U, K, and u 0 w 0 profiles when compared to single-equation models.

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“…Although there has been some work testing second-order closure model for homogeneous canopy flows (e.g. Ayotte et al, 1999;Pinard and Wilson, 2001), this has not yet been applied to inhomogeneous canopies, and so it is not possible to do the same comparison as BXH between analytical solution and second-order numerical model for the present problem.…”

Section: Impact Of the Closure Assumptionsmentioning

confidence: 99%

Boundary‐layer flow within and above a forest canopy of variable density

Ross

2011

Quart J Royal Meteoro Soc

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An analytical model is developed for flow within and above a forest canopy with a slowly varying canopy density. Results are compared with existing analytical models for flow over a surface with slowly varying roughness length, and also with numerical simulations. The results show that the analytical solution is successful in capturing the behaviour of the flow for small and slowly changing variations in canopy density. Previous models which only vary the roughness length and neglect changes in displacement height fail to capture the near-surface flow accurately. Including changes in displacement height as well as roughness length changes gives results closer to those obtained with the full canopy model, but even then the flow induced in the canopy leads to significant differences. The analytical model also highlights the sensitivity of the results to the parametrization of the vertical component of the turbulent stress tensor, τ zz . For shorter wavelength variations in the canopy density, the analytical model breaks down as the more rapid changes in density induce larger flow perturbations which lead to increased flow into and out of the canopy. This kind of idealised analytical study provides important insights into the role of canopy heterogeneities on boundary-layer flow. This is important both for understanding near-surface winds and transport, and also for parametrizing the effects of surface heterogeneities in large-scale weather and climate models.

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A Second-Order Closure for Neutrally Stratified Vegetative Canopy Flows

Cited by 97 publications

References 27 publications

Wind fields in heterogeneous conifer canopies: parameterisation of momentum absorption using high-resolution 3D vegetation scans

Wind fields in heterogeneous conifer canopies: parameterisation of momentum absorption using high-resolution 3D vegetation scans

ONE- and TWO-Equation Models for Canopy Turbulence

Boundary‐layer flow within and above a forest canopy of variable density

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