A numerical study of near-field dispersion within and above forest canopies

Pheromone releases are used by forest managers as an anti-aggregation technique to protect high value forest stands against the bark beetle.  As a result, near-field pheromone dispersion patterns are of interest for developing forest management techniques.  Recent field campaigns have studied the dispersion of a tracer gas released from a point source in several different types of forest canopies.  The objective of this paper is to investigate the feasibility of simulating turbulent transport within a forest canopy using a commercial Computational Fluid Dynamics (CFD) code.  As a first step, Fluent was used to predict near-field concentrations of a tracer gas in a Lodgepole Pine canopy.  Two different turbulence closure models, the k-ε model and the Reynolds Stress Model (RSM), were used in the simulations.  A porous media based on the Leaf Area Index (LAI) profiles, was used to simulate the effects of the canopy.  Solar radiation effects on the canopy and ground were used to account for the development of a convective boundary layer above the canopy. Normalized concentrations for different downstream distances were compared to experimental results as a basis for evaluation of the model performance.