林带冬季相疏透度与透风系数的换算

Conversion of Porosity and Permeability of Shelter Belts with Winter Facies

为得到较为准确的林带冬季相疏透度与透风系数换算公式,利用阻力形成的物理机制推导不同行数圆柱体栅栏的疏透度与透风系数近似换算公式,揭示不同行数林带防风效应物理机制的一致性和数值差异规律。结果表明,疏透度β相同的林带,行数越少透风系数α越小,防风效果越好。以几何相似程度接近为原则,给出林带冬季相透风系数α与疏透度β的近似换算关系:单行林带为α=β0.7,2行林带为α=β0.6,多行林带为α=β0.55,比忽略行数和季相的影响而采用宽高比近于1的林带实验模拟公式α=β0.4更符合实际,有助于准确理解和运用防风效应原理进行林带和林网的结构设计。

In order to get more accurate forest winter facies porosity and permeability conversion formula, the physical mechanism of the resistance formation was used to deduce an approximate conversion formula of cylindrical fence porosity and permeability with different rows of trees, for revealing the consistency and the numerical variation rule of windbreak effect and the physical mechanism with different row numbers. The results showed that with the shelterbelt with the same porosity β, the less the row number, the smaller the permeability α, and the better the windbreak effect. With geometry similarity approaching as the principle, approximate conversion relationships between the forest winter phase permeability a, and porosity β were developed： single belt α=β^0.7, two belt α=β^0.6, for multiple belts α=β^0.55, which was more actual than the belt simulation formula α=β^0.4 which ignores rows and seasonal aspect effects, and assumes the ratio of length and height close to 1. The new relationships conduced to accurately understanding and applying windbreak effect principle and structure design of forest shelter belts.