Numerical Simulation of the Airflow Across Trees in a Windbreak

Abstract

The flow across a three-dimensional (3-D) windbreak comprising individual cypress trees is studied to establish the significance and extent of the 3-D flow patterns. The cypress tree is modelled as a solid cylindrical stem and a conic porous canopy. Cases with a single row of trees or two rows of trees with different distances between the rows are considered; in the case of a single row, several densities of the canopy are used. The steady Reynoldsaveraged Navier-Stokes (RANS) approximation is solved using a commercial computational fluid dynamics (CFD) package and a high-resolution mesh. Three-dimensional flow is found in the vicinity of the windbreak up to a leeward distance of 1-2 tree-heights, depending on the density of the canopy, and is manifest as significant lateral variations and reduced vertical flow. At larger leeward distances, a two-dimensional (2-D) flow is established with characteristics similar to existing 2-D studies; the flow leeward of the last row is insensitive to the distance between the rows. Homogeneous 2-D windbreak models are found to be inaccurate in the vicinity of the windbreak. This is exactly the region that needs to be sheltered in many cases, since the inner vegetation is anyway protected by the outer vegetation.

PIV analysis on the shelter effect of a bank of real fir trees

“…For a windbreak with porosity similar to that featured in the present study, air flow in the lower part of the canopy was inclined upward to the upper part, whereas a large-scale recirculation zone was not observed (Gross, 1987;Melese et al, 2009;Rosenfeld et al, 2010). This flow features different from the present study is mainly caused by the configuration of a real three-dimensional (3-D) tree.…”

“…For an accurate understanding of the shelter effect of natural windbreaks, windbreak of non-uniform porosity with finite thickness should be investigated systematically. This kind of demand on basic academic research has been mentioned by many researchers (Wang et al, 2001;Zhou et al, 2004;Rosenfeld et al, 2010). To our knowledge, however, no attempt has been made to conduct an in-depth investigation of windbreaks.…”

Structural design of a natural windbreak using computational and experimental modeling

“…Wilson [18] analyzed the use of several models, and concluded that results are nearly insensitive to the turbulence model. The turbulence model chosen for this study, as available in the commercial software, has its standard formulation, and then does not includes the extrasource terms [11,13], necessary to account for the influence of vegetation on the turbulence budget, as used by Rosenfeld et al [10].…”

Numerical Simulation of Airflow Structure and Dust Emissions behind Porous Fences Used to Shelter Open Storage Piles

“…The RNG k-ε turbulence model was judged to be suitable to compute the separated shear flow (Kim et al, 1997). Airflow is assumed to be viscous, incompressible, isothermal, and steady (Chen et al, 2012), and the governing equations used to determine the continuous flow are as follows (Rosenfeld et al, 2010).…”