LES study on the turbulent flow fields over complex terrain covered by vegetation canopy

Liu, Zhengqing; Ishihara, Takeshi; He, Xuhui; Niu, Huawei

doi:10.1016/j.jweia.2016.05.002

Cited by 53 publications

(24 citation statements)

References 16 publications

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“…; Ross and Harman, ; Liu et al . ). However, a limited number of studies have been devoted to scalar exchanges and how they may be impacted by such recirculation zone.…”

Section: Introductionmentioning

confidence: 98%

“…The potential impact of flow separation and the consequent recirculation zone within the canopy on the transport of gases and even particles such as seeds, pollen, or aerosols has been discussed by many authors (e.g. Finnigan and Belcher, 2004;Katul et al, 2006;Katul and Poggi, 2010;Xu and Yi, 2013;Trakhtenbrot et al, 2014;Ross and Harman, 2015;Liu et al, 2016). However, a limited number of studies have been devoted to scalar exchanges and how they may be impacted by such recirculation zone.…”

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confidence: 99%

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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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“…; Ross and Harman, ; Liu et al . ). However, a limited number of studies have been devoted to scalar exchanges and how they may be impacted by such recirculation zone.…”

Section: Introductionmentioning

confidence: 98%

mentioning

confidence: 99%

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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“…Most of these features have been supported by LES studies of idealized topography such as isolated ridges (Dupont et al, 2008) and hills (Liu et al, 2019; Patton & Katul, 2009). The few studies that include real topography have focused on steeper slopes, for which separation would occur even in the absence of canopy cover (e.g., Grant et al, 2015, 2016; Liu et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Effects of Gentle Topography on Forest‐Atmosphere Gas Exchanges and Implications for Eddy‐Covariance Measurements

2020

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The interpretation of tower‐based eddy‐covariance (EC) turbulent flux measurements above forests hinges on three key assumptions: (1) steadiness in the flow statistics, (2) planar homogeneity of scalar sources or sinks, and (3) planar homogeneity in the flow statistics. Large eddy simulations (LESs) were used to control the first two so as to explore the break‐down of the third for idealized and real gentle topography such as those encountered in Amazonia. The LES runs were conducted using uniformly distributed sources inside homogeneous forests covering complex terrain to link the spatial patterns of scalar turbulent fluxes to topographic features. Results showed strong modulation of the fluxes by flow features induced by topography, including large area with negative fluxes compensating “chimney” regions with fluxes almost an order of magnitude larger than the landscape flux. Significant spatial heterogeneity persisted up to at least two canopy heights, where most eddy‐covariance measurements are performed above tall forests. A heterogeneity index was introduced to characterize and contrast different scenarios, and a topography categorization was shown to have predictive capabilities in identifying regions of negative and enhanced fluxes.

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“…The time-dependent terms of the equations are interpolated by the second order implicit scheme. The coupling between pressure and velocity in momentum equation is implemented by SIMPLE algorithm, which was shown by Liu et al (2016).…”

Section: Fluid Dynamicsmentioning

confidence: 99%

Coupled Analysis of Unsteady Aerodynamics and Vehicle Motion of a Passenger Car in Crosswind Condition

Huang

Feng

2017

JAFM

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High-speed passenger car requires a lighter weight for improving power performance and reducing fuel consumption; a car with higher-speed and lighter weight will lead to the passenger car more sensitive to the crosswind, which will affect the stability and drivability of the passenger car. This study employs the fully-coupled method to investigate a passenger car subjected "1-cos" crosswind with consideration of the vehicle motion. Large eddy simulation (LES) and dynamic mesh is adopted to investigate the unsteady aerodynamic, and the vehicle is treated as a three-freedom-system and driver's control is considered to investigate the vehicle dynamic. The one-way simulation and quasi-steady simulation are also conducted to compare with the fully-coupled simulation. The results of the three simulation methods show large difference. The peak value of the lateral displacement in fully-coupled simulation is the smallest between the three simulation approaches. While the change of aerodynamic loads and vehicle motion in fully-coupled simulation is more complicated than in one-way and quasi-steady simulation. These results clearly indicate the significance of including of the unsteady aerodynamic loads in passenger car moving analysis.

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LES study on the turbulent flow fields over complex terrain covered by vegetation canopy

Cited by 53 publications

References 16 publications

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

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

Effects of Gentle Topography on Forest‐Atmosphere Gas Exchanges and Implications for Eddy‐Covariance Measurements

Coupled Analysis of Unsteady Aerodynamics and Vehicle Motion of a Passenger Car in Crosswind Condition

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