基于流体仿真的椭球型树冠抗风性能研究

近年来,随着全球气候频繁变化,台风等极端灾害性天气发生频率加剧,森林正面临着潜在的巨大损害。台风产生的风压、风速、湍流强度施加于林木上,使得林木风倒频繁发生。因此,研究树木的抗风性能有着重要意义。使用计算机仿真数值模拟方法对流场在林分中的运动进行求取,主要方法如下:首先通过GAMBIT对三维树冠进行树木建模并进行网格划分,其次使用标准k-ε方程组对三维树冠的流场分布进行模拟。最后通过模拟计算得到不同叶面积指数对应的树冠周围压力场、风速、湍动能分布。结果表明:对于单株树,当树冠孔隙度从0.25变化到0.75,即叶面积指数从2.77变化到0.58时,冠内风速在树冠内的波动幅度从8.0 m/s下降到4.0m/s,树冠内压力的波动幅度从229.0 Pa下降到到143.5 Pa,湍流强度的波动幅度从6.03%降到3.40%;对于林冠来说,当孔隙度从0.25变化到0.75,即叶面积指数从2.77变化到0.58时,在林冠前后的风速差从17.67 m/s变化为15.89 m/s,压力差从180.38 Pa变化到117.38 Pa,湍流强度的变化幅度从4.0%变化到2.4%。由于树冠前后压差过大和树冠内风速差过大会导致树的结构遭到破坏,因此,越稀疏的林冠,抗风性能越好。

Research on wind resistance of tree with ellipsoid shape crown based on fluid simulation

In recent years, due to the frequent changes in global climate, the frequency and strength of typhoon, as well as the extremely weather disasters have terrified. At the same time, forests are suffered tremendous damages.Wind pressure, speed and turbulence intensity generated by typhoon are applied to trees in forest, causing wind strength fall frequently. Therefore, it is of great significance to investigate the wind resistance of trees. In this study, the numerical method of computer simulation was used to analyze the movement of the flow field in the forest. The main methods were as follows:firstly, the three-dimensional canopy was modeled and meshed by GAMBIT, and then the standard k-ε equations were used to simulate the flow field of three-dimensional canopy. Finally, the distributions of the pressure, wind speed, and turbulent intensity were calculated by the simulated calculation. The results showed that, for a single tree, when the crown s porosity changed from 0.25 to 0.75, the leaf area index ( I LAI ) varied from 2.77 to 0.58, and the wind speed fluctuation within the canopy decreased from 8.0 m/s to 4.0 m/s.The fluctuation range of the internal pressure dropped from 229.0 Pa to 143.5 Pa, and the fluctuation of turbulence intensity dropped from 6.03% to 3.40%. For three tree crowns constituting a forest canopy, when the porosity changed from 0.25 to 0.75 , the I LAI changed from 2.77 to 0.58. At the same time, the wind speed difference before and after canopies changed from 17.67 m/s to 15.89 m/s,the pressure difference was changed from 180.38 Pa to 117.38 Pa, and the range of turbulence intensity was changed from 4.0% to 2.4%. As the large pressure difference between the front and the rear of the canopy and the large wind speed difference in the canopy would cause the structure of the tree to be destroyed, it can be seen that the sparser canopy was, the better the wind resistance performance could be obtained.