摘要
【目的】研究强风力扰动下不同林冠形状的森林内部风场分布情况,为防风林营造与种植过程中树种的选择提供理论依据。【方法】首先建立3种不同冠形林分模型(其中冠部为多孔介质模型),并根据冠形对应树种的消光系数确定多孔介质的孔隙率与叶面积指数(leaf area index, LAI)的关系;然后以k-ε湍流模型为基础,在动量方程中添加源项,建立三维树冠流计算模型,计算3种冠形在强风力下林分内部各处风速、风压与湍流动能强度。【结果】圆锥形林冠林内风速最小值(0.047 m/s)与圆台形林冠林内风速最小值(0.076 m/s)相差0.029 m/s。椭球形林冠林内风速最小值为0.940 m/s,且波动大于其他冠形。圆锥形林冠林内压差与湍流动能强度均最小,分别为30.22 Pa和0.17%。椭球形林冠林内压差最大,压差均值为62.14 Pa。圆台形林冠林内湍流强度最大,最大值为25.19%。【结论】结合湍流动能强度对树木抗风安全性的影响,以及风速的降低和压差减少作用,在构建防风林体系时,应选择与圆锥形林冠特点相似树冠的树种,使得防风林的抗风效果更强。
【Objective】 Studying the distribution of wind fields inside forests with different canopy shapes under strong wind disturbance can provide a theoretical basis for the selection of tree species in windbreak forest construction and planting.【Method】 First, we established three different forest models with different canopy shapes, in which the canopy structure was simulated using porous media. The relationship between the porosity of the medium and the leaf area index(LAI) was determined from the extinction coefficient of the corresponding tree species. Then, based on the k-ε equation turbulence model, we added source terms into the momentum equation to calculate wind velocity, pressure, and turbulent energy intensity of different canopy shapes under strong wind loads. 【Result】The difference between the minimum wind speed in the conical canopy forest(0.047 m/s) and the minimum wind speed in the truncated-conical canopy forest(0.076 m/s) was 0.029 m/s. The minimum wind speed in the ellipsoidal canopy was 0.940 m/s, and the fluctuation was greater than for other crowns. The conical canopy forest had the lowest difference in pressure(30.22 Pa) and turbulent kinetic energy(0.17%). The pressure difference in the ellipsoidal canopy forest was the largest(mean: 62.14 Pa). Turbulence intensity in the truncated-conical canopy forest was the largest, with a maximum of 25.19%.【Conclusion】The method proposed in this paper solved the problem that wind factors such as turbulent kinetic energy intensity and differential pressure at real time cannot obtain due to the complexity of the tree canopy. Because of the influence of turbulent energy intensity on the wind-resistant safety of trees and the reduction of wind speed and pressure difference, crowns with characteristics similar to the conical canopy should be selected when constructing a wind-proof forest system.
引文
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