Large-eddy simulation of low-level jet-like flow in a canopy |
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Authors: | Shaolin Mao Z -G Feng Efstathios E Michaelides |
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Institution: | (1) Department of Mechanical and Energy Engineering, University of North Texas, Denton, TX 76203, USA |
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Abstract: | The computational method of Large-Eddy Simulations has been used to study the weak, neutrally stable drainage flow within
tree canopies. The computational results show that a secondary velocity maximum that resembles a jet is formed within the
canopy under the nocturnal flow conditions. This jet-like flow is important in the analysis and measurements of the net ecosystem-atmosphere
exchange (NEE) for carbon dioxide (CO2). A uniformly distributed, plane source was placed within the canopy in order to simulate the nocturnal production of CO2. The NEE is calculated as the sum of the integration of the rate of change of the concentration of CO2 over the computational domain, the vertical turbulent flux measured directly by eddy-covariance (EC) method, and the advection
terms, which are not taken into account in the EC method. Numerical results of the velocity and concentration fields, within
and above the canopy, are presented and their impact on the CO2 transport is investigated in detail. The computational results show that 15–20% of NEE is drained out by the advection process
under the canopy. The results also show that the turbulent fluctuations in the lateral direction are also significant and
may result in 2–5% CO2 transport. |
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Keywords: | Large-Eddy Simulation (LES) Canopy Stable boundary layer Nocturnal conditions Net ecosystem exchange |
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