Estimation of the three-dimensional aerodynamic structure of a green ash shelterbelt

摘要

The three-dimensional aerodynamic structure of a tree shelterbelt is described by two structural descriptors: vegetative surface area density (vegetative surface area per unit canopy volume) and cubic density (vegetative volume per unit canopy volume). Based on destructive measurements, estimates of both descriptors for a two-row 31-year-old green ash (Fraxinus pennsylvanica Marsh.) shelterbelt are developed. In order to estimate the structural descriptors in three dimensions based on data measured in two dimensions, equations to predict vegetative surface area and volume, their marginal distribution with height, and their marginal distribution across width at a given height are derived for each tree component: trunk, branches, leaves and seeds. Theprocedure to use these equations to estimate the structure of the green ash shelterbelt either in three dimensions or in the width and height dimensions is demonstrated. The estimated structure can be used to test current models of turbulence through atree shelterbelt under a field conditions, and to simulate the wind fields as influenced by the actual structure of a tree shelterbelt. The developed equation can be used to generate the three-dimensional structure of a shelterbelt with a design similarto the sampled shelterbelts or a shelterbelt of green ash mixed with other species similar to those in the sampled shelterbelts. Thus, the boundary-layer flows as influenced by the overall structure of tree shelterbelts with different designs can be numerically simulated. These simulated results can provide guidance for shelterbelt design.