The Effects of Vegetation Density on Coherent Turbulent Structures within the Canopy Sublayer: A Large-Eddy Simulation Study

Huang, Jing; Cassiani, Massimo; Albertson, J. D.

doi:10.1007/s10546-009-9423-1

Cited by 41 publications

(51 citation statements)

References 46 publications

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“…This structure has been compared to the longitudinal roll vortex observed in field studies (Wilson 1996). The coherent structures within the canopy sublayer (CSL) have been demonstrated to be similar to those found in the ABL in the sense that they also consist of a strong sweep or ejection motion framed between a pair of streamwise vortices (Finnigan and Shaw 2000;Huang et al 2009b). However, the coherent structures represent a greater fraction of the TKE in the canopy sublayer than in the atmospheric surface layer (ASL) (Finnigan and Shaw 2000).…”

Section: Introductionmentioning

confidence: 89%

Coherent Turbulent Structures Across a Vegetation Discontinuity

Huang

Cassiani

Albertson

2011

Boundary-Layer Meteorol

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The study of turbulent flow across a vegetation discontinuity is of significant interest as such landscape features are common, and as there is no available theory to describe this regime adequately. We have simulated the three-dimensional dynamics of the airflow across a discontinuity between a forest (with a leaf area index of 4) and a clearing surface using large-eddy simulation. The properties of the bulk flow, as well as the large-scale coherent turbulent structures across the forest-to-clearing transition and the clearing-toforest transition, are systematically explored. The vertical transport of the bulk flow upstream of the leading edge gives rise to the enhanced gust zone around the canopy top, while the transport downstream of the trailing edge leads to the formation of a recirculation zone above the clearing surface. The large-scale coherent structures across the two transitions exhibit both similarities with and differences from those upstream of the corresponding transition. For example, the ejection motion is dominant over the sweep motion in most of the region 1 < z/ h < 2 (h is the canopy height) immediately downstream of the trailing edge, much as in the forested area upstream. Also, the streamwise vortex pair, which has previously been observed within the canopy sublayer and the atmospheric boundary layer, is consistently found across both transitions. However, the inflection observed both in the mean streamwise velocity, as well as in the vertical profiles of the coherent structures in the forested area, disappears gradually across the forest-to-clearing transition. The coherence of the turbulence, quantified by the percentage of the total turbulence kinetic energy that the coherent structures capture from the flow, decreases sharply immediately downstream of the trailing edge 123 2 J. Huang et al.of the forest and increases downstream of the leading edge of the forest. The effects of the ratio of the forest/clearing lengths under a given streamwise periodicity on flow statistics and coherent turbulent structures are presented as well.

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Section: Introductionmentioning

confidence: 89%

Coherent Turbulent Structures Across a Vegetation Discontinuity

Huang

Cassiani

Albertson

2011

Boundary-Layer Meteorol

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“…Poggi and Katul (2007b) and Ross and Vosper (2005) have shown that the analytical model fails to model the flow pattern on dense canopies on narrow hills. Third, even though turbulence closure models and large eddy simulation models have been used to simulate flow within and above the canopy in numerous published studies, most numerically reproduced canopy flow is confined to idealized cases: either neutral (Ross and Vosper, 2005;Dupont et al, 2008;Ross, 2008) or weakly unstable (Wang, 2010) atmospheric conditions, or flat terrain with a homogeneous and extensive canopy (Huang et al, 2009;Dupont et al, 2010).…”

Section: Xu Et Al: Stably Stratified Canopy Flow In Complex Terrainmentioning

confidence: 99%

Stably stratified canopy flow in complex terrain

Kutter

2015

Atmos. Chem. Phys.

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Abstract. Stably stratified canopy flow in complex terrain has been considered a difficult condition for measuring net ecosystem-atmosphere exchanges of carbon, water vapor, and energy. A long-standing advection error in eddy-flux measurements is caused by stably stratified canopy flow. Such a condition with strong thermal gradient and less turbulent air is also difficult for modeling. To understand the challenging atmospheric condition for eddy-flux measurements, we use the renormalized group (RNG) k-ε turbulence model to investigate the main characteristics of stably stratified canopy flows in complex terrain. In this twodimensional simulation, we imposed persistent constant heat flux at ground surface and linearly increasing cooling rate in the upper-canopy layer, vertically varying dissipative force from canopy drag elements, buoyancy forcing induced from thermal stratification and the hill terrain. These strong boundary effects keep nonlinearity in the two-dimensional NavierStokes equations high enough to generate turbulent behavior. The fundamental characteristics of nighttime canopy flow over complex terrain measured by the small number of available multi-tower advection experiments can be reproduced by this numerical simulation, such as (1) unstable layer in the canopy and super-stable layers associated with flow decoupling in deep canopy and near the top of canopy; (2) sub-canopy drainage flow and drainage flow near the top of canopy in calm night; (3) upward momentum transfer in canopy, downward heat transfer in upper canopy and upward heat transfer in deep canopy; and (4) large buoyancy suppression and weak shear production in strong stability.

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“…Patton and Katul (2009) explored the spatial perturbations of the first and second moments of the velocity and pressure fields for flow over a train of gentle hills covered by sparse or dense vegetation represented by uniformly arrayed rods each with a height that is comparable to the hill height. The proper orthogonal decomposition (POD) technique was used by Huang et al (2009) to study the effects of vegetation density on basic flow statistics and large-scale coherent turbulent structures within the canopy sublayer using five different vegetation densities varying from an extremely sparse canopy to an extremely dense canopy. All of the above approaches used large-eddy simulation (LES); unfortunately it is numerically demanding when a more detailed investigation at a plant or even at a branch level is desired.…”

Section: Introductionmentioning

confidence: 99%

Modelling the Effect of Tree Foliage on Sprayer Airflow in Orchards

Endalew

Debaer²,

Rutten³

et al. 2010

Boundary-Layer Meteorol

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The effect of tree foliage on sprayer airflow through pear trees in a fruit orchard was studied and modelled in detail. A new three-dimensional (3-D) computational fluid dynamics model that integrates the 3-D canopy architecture with a local closure model to simulate the effect of the stem and branches and leaves of trees separately on airflow was developed. The model was validated with field observations made in an experimental orchard (pcfruit, Sint-Truiden, Belgium) in spring and summer 2008 and was used to investigate the airflow from three air-assisted orchard sprayers (Condor V, Duoprop and AirJet quatt). Velocity magnitudes were measured before and behind leafless and fully-leafed pear canopies across the row while the operating sprayers are passing along the row, and were compared with the simulations. The simulation results predicted the measured values well with all the local relative errors within 20%. The effect of foliar density on airflow from the three air assisted sprayers was manifested by changing the magnitude and direction of the sprayers' air velocity behind the canopy, especially at the denser regions of the canopy and by changing the pattern of velocity decay horizontally along the jet. The developed methodology will also allow a thorough investigation of atmospheric airflow in canopy structures.

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The Effects of Vegetation Density on Coherent Turbulent Structures within the Canopy Sublayer: A Large-Eddy Simulation Study

Cited by 41 publications

References 46 publications

Coherent Turbulent Structures Across a Vegetation Discontinuity

Coherent Turbulent Structures Across a Vegetation Discontinuity

Stably stratified canopy flow in complex terrain

Modelling the Effect of Tree Foliage on Sprayer Airflow in Orchards

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