The Effects of Forest Canopy Models on Damping of Turbulent Energy in a Flow

本研究主要由三个部分组成；(1)第一种是介质风洞实验，(2)第二种是大风洞实验，(3)第三种是有限差分法和分子动力学等冠粒动力学的数值模拟。(1)本试验冠层模型叶面积指数为6.6。利用CTA测量了模型下游区域的流向速度分量分布。单个树模型之间的流动不同于树的下游流动。冠层模型的下游水流表现出较强的三维特征。(2) 1998年1月在宫崎大学建造的大型风洞进行了试验。冠层模型的叶面积指数为9.0。林冠上剪切层的时间平均速度和湍流强度随不同节距的排列而变化。(3)采用FDM-SMAC方法对流场进行模拟。冠层的冠层由大量的粒子近似而成，这些粒子通过弹簧和阻尼器与邻近的粒子相连接。气流的运动和冠内粒子的运动在时间上是联系在一起的。对不同稀疏冠层和稠密冠层的流场进行了数值计算。这些结果与风洞试验结果吻合较好。

This research is composed of three parts ; (1) the first is the experiments with the medium wind tunnel, (2) the second is that with the large wind tunnel, and (3) the third is the numerical simulation with the finite difference method and the crown-particle dynamics like the molecular dynamics.(1) The canopy model in this testing has the leaf area index of 6.6. Distributions of streamwise velocity components in the downstream region of the model are measured with the CTA.Flows between individual tree models are different from flows downstream of trees. Flows downstream of the canopy models showed strong three-dimensional characteristics.(2) This testing is experimented with the large wind tunnel constructed in Miyazaki University on January 1998. The canopy model has the leaf area index of 9.0. Distributions of the time-averaged velocity and intensity of turbulence in the shear-layer above the canopy are changed with the different pitch from arrangement of individual tree models.(3) Flow fields are simulated with the FDM-SMAC method. The crowns of canopy are approximated with a lot of particles that are connected with neighbor particles by spring and damper. The motion of air flows and the motion of particles in the crown are linked in the time-marching. Flow fields around the canopies of various sparse and dense crowns are calculated numerically. These results are good agreement with the results of the experiments with the wind tunnel testing.