Numerical simulation of turbulent kinetic energy downwind of varying-width shelters

摘要

Windbreaks and shelterbelts appear in many agricultural and forestry scenarios. In a forestry situation where cutblocks alternate with stands, often there is concern about wind-throw both in the remaining trees and for the regrowth. There is strong evidence (Gardiner, 1994) that it is the gustiness, or turbulence, rather than mean wind, which knocks over the trees. Recently Wilson and Flesch (1999) conducted a numerical simulation of varying width shelterbelts within successive cutblocks. One of the conclusions from their work was that turbulence in the cleared area downwind of the wider shelter was greater than behind the narrower belt. They explain this phenomenon by suggesting that perhaps the wider shelter provides greater mean wind reduction, leading to greater shear stress and its consequent turbulent energy production. The purpose of this study was to examine the effect of shelterbelt width on both mean and turbulent variables. A wind tunnel model was used in which we generated upstream turbulence resembling an equilibrated forest flow. This was followed by a clearing of 10h (where h is tree height), and then the windbreaks, consisting of model trees. Four treatments were run, consisting of 1, 2, 4 and 8-rows of trees. These same configurations were also simulated using the numerical model developed by Wilson et al. (1998).