Scalar Transport over Forested Hills

Ross, Andrew

doi:10.1007/s10546-011-9628-y

Cited by 29 publications

(34 citation statements)

References 26 publications

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“…Chen et al [60] Pollutant dispersion in the built environment Exp/Num − Sc t = 1.0 and corrected from wind tunnel data Hassan et al [65] Supersonic crossflow Exp/Num − Sc t = 1.0 and adaptive Sc t Galeazzo et al [64] Jet in crossflow Exp/Num − Sc t = 0.3-0.9 Goldberg et al [70] Different type of air flows Exp/Num − Sc t variable Ross [71] Flow over forested hills Exp/Num − Sc t = Sc t (z)…”

Section: Environmental Flow Commentsmentioning

confidence: 99%

“…Ross [71] performed numerical simulations of scalar transport in neutral flow over forested hills using both a 1.5-order mixing-length closure scheme and LES. He found that the common assumption that momentum and scalars are transported in the same way is not valid within and just above the canopies, with strong variations in Sc t in the vertical direction and across the hill.…”

Section: Environmental Flow Commentsmentioning

confidence: 99%

“…A second group of studies investigated the question if Sct is a constant or it is varying inside the flow domain [66,[70][71][72]. Koeltzsch [66] carried out wind tunnel experiments in a turbulent boundary layer above a flat plate.…”

Section: Contaminant Dispersion Due To Transverse Turbulent Mixing Inmentioning

confidence: 99%

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On the Values for the Turbulent Schmidt Number in Environmental Flows

Gualtieri

Angeloudis

Bombardelli

et al. 2017

Fluids

171

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Computational Fluid Dynamics (CFD) has consolidated as a tool to provide understanding and quantitative information regarding many complex environmental flows. The accuracy and reliability of CFD modelling results oftentimes come under scrutiny because of issues in the implementation of and input data for those simulations. Regarding the input data, if an approach based on the Reynolds-Averaged Navier-Stokes (RANS) equations is applied, the turbulent scalar fluxes are generally estimated by assuming the standard gradient diffusion hypothesis (SGDH), which requires the definition of the turbulent Schmidt number, Sc t (the ratio of momentum diffusivity to mass diffusivity in the turbulent flow). However, no universally-accepted values of this parameter have been established or, more importantly, methodologies for its computation have been provided. This paper firstly presents a review of previous studies about Sc t in environmental flows, involving both water and air systems. Secondly, three case studies are presented where the key role of a correct parameterization of the turbulent Schmidt number is pointed out. These include: (1) transverse mixing in a shallow water flow; (2) tracer transport in a contact tank; and (3) sediment transport in suspension. An overall picture on the use of the Schmidt number in CFD emerges from the paper.

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Section: Environmental Flow Commentsmentioning

confidence: 99%

Section: Environmental Flow Commentsmentioning

confidence: 99%

See 1 more Smart Citation

On the Values for the Turbulent Schmidt Number in Environmental Flows

Gualtieri

Angeloudis

Bombardelli

et al. 2017

Fluids

171

View full text Add to dashboard Cite

show abstract

“…() found that gentle topography (sinusoidal ridges) led to significant spatial variability in fluxes of C O 2 at the canopy top when photosynthetic sinks and soil respiration sources are considered together. Two‐dimensional model runs reported by Ross () using a uniform gas source within the entire canopy volume confirms the existence of enhanced fluxes in the separation region. Their results also showed that the efficiency of gas transport out of the canopy is enhanced by topography, leading to lower in‐canopy concentrations when compared to flat terrain.…”

Section: Introductionmentioning

confidence: 97%

Effects of topography on in‐canopy transport of gases emitted within dense forests

Chen

Chamecki

Katul

2019

Quart J Royal Meteoro Soc

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The significance of air flow within dense canopies situated on hilly terrain is not in dispute given its relevance to a plethora of applications in meteorology, wind energy, air pollution, atmospheric chemistry and ecology. While the mathematical description of such flows is complex, progress has proceeded through an interplay between experiments, mathematical modelling, and more recently large‐eddy simulations (LESs). In this contribution, LES is used to investigate the topography‐induced changes in the flow field and how these changes propagate to scalar transport within the canopy. The LES runs are conducted for a neutral atmospheric boundary layer above a tall dense forested canopy situated on a train of two‐dimensional sinusoidal hills. The foliage distribution is specified using leaf area density measurements collected in an Amazon rain forest. A series of LES runs with increasing hill amplitude are conducted to disturb the flow from its flat‐terrain state. The LES runs successfully reproduce the recirculation region and the flow separation on the lee‐side of the hill within the canopy region in agreement with prior laboratory and LES studies. Simulation results show that air parcels released inside the canopy have two preferential pathways to escape the canopy region: a “local” pathway similar to that encountered in flat terrain and an “advective” pathway near the flow‐separation region. Further analysis shows that the preferential escape location over the flow‐separation region leads to a “chimney”‐like effect that becomes amplified for air parcel releases near the forest floor. The work here demonstrates that shear‐layer turbulence is the main mechanism exporting air parcels out the canopy for both pathways. However, compared to flat terrain, the mean updraught at the flow separation induced by topography significantly shortens the in‐canopy residence time for air parcels released in the lower canopy, thus enhancing the export fraction of reactive gases.

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“…BLASIUS has previously been used for other studies of canopy flow, both as a one-and-a-half order mixing-length closure model (Ross and Vosper, 2005;Ross, 2011), and as a large-eddy simulation (LES) model (Ross, 2008(Ross, , 2011. Here the model is run with the one-and-a-half order mixing-length closure scheme.…”

Section: Long and Short Wavelength Variations In Canopy Densitymentioning

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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Scalar Transport over Forested Hills

Cited by 29 publications

References 26 publications

On the Values for the Turbulent Schmidt Number in Environmental Flows

On the Values for the Turbulent Schmidt Number in Environmental Flows

Effects of topography on in‐canopy transport of gases emitted within dense forests

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

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