基于格子-玻尔兹曼方法的三维虚拟树冠阻力特性

Resistance Characteristics of 3D Virtual Tree Canopy Based on Lattice-Boltzmann Method

为了给预测实际树冠的风阻提供理论依据,运用Visual Basic程序设计语言建立三维虚拟树冠模型,使用基于格子-玻尔兹曼方法(Lattice-Boltzmann method,LBM)的计算流体动力学软件——XFlow进行模拟计算,研究不同叶面积指数和风速条件下,树冠对空气流动阻力特性的影响。采用叶面积指数表征树冠的形态结构特征,讨论其对树冠流动阻力的影响规律,并提出阻力系数与叶面积指数、风速之间的关联表达式。利用风洞对人工树模型进行试验,测试结果与关联表达式的预测结果吻合较好。研究结果表明:树冠的阻力系数与叶面积指数、风速呈指数函数关系;当风速大于5m/s时,阻力系数接近常数,风速对阻力系数的影响不再显著。

To provide a theoretical basis for predicting the wind resistance of the actual canopy,the resistance of the canopy on the airflow was studied by XFlow which was based on the Lattice-Boltzmann method(LBM)under different leaf area indexes and wind speeds.The models used in the simulation were 3 D virtual canopy models,which were established by Visual Basic for Application(VBA).Leaf area index could represent the morphological structure of the canopy,and its influence on the flow resistance of canopy was studied.The related expression of drag coefficient with leaf area index and wind speed was put forward.An experiment was carried out on the artificial trees in the wind tunnel,and the experimental results were in good agreement with the predictions of the expressions.The study shows that the exponential function is able to describe the relationship among the drag coefficient of the canopy and leaf area index and the wind speed.The drag coefficient is close to the constant when the wind speed is greater than 5 m/s,which means that the effect of the wind speed on the drag coefficient is not significant.