Gaseous Plume Diffusion Characteristics within Model Peg Canopies

摘要

A point source of an air-helium mixture was released continuously at various positions within a simulated canopy composed of 9 cm high pegs, 0.48 cm diameter, spaced in several arrays (2.54 x 2.54, 3.55 x 3.55, and 5.08 x 5.08 cm). Variations of the vertical location of the source revealed the strongly nonisotropic character of diffusion within a canopy with respect to the relative diffusion rates in the lateral and vertical directions. When the source was placed at various downstream distances from the edge of the canopy, it displayed a tendency to exhale the plume near the front of the model canopy and to inhale the plume at distances further downstream. Calculations of the turbulent diffusion coefficient, K, within and above the canopy from the experimental data, reveal both a constant region and a region of linear increase with height increase as suggested by previous authors. (Author)