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Numerical Research Of The Characteristics Of Wind Flow Near The Forest Underlying Surface

Posted on:2016-07-02Degree:MasterType:Thesis
Country:ChinaCandidate:A JiangFull Text:PDF
GTID:2180330461967212Subject:Engineering Mechanics
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Vegetation underlying surface has great effect on controlling soil erosion and sand blown, so the study of the flow field near vegetation underlying surface has great theoretical and practical value. Because of the complexity of the vegetation underlying surface vegetation, most studies of flow field were experimental observations. Based on previous work, this paper improved the calculation model of flow field near and in vegetation underlying surface, and the characteristics of the flow field were studied. In addition, the influences of leaf area index and stand density on aerodynamic roughness length, zero-displacement, friction velocity were researched. The main contents are as follows:1. First, the mathematical model for calculating the flow field around vegetation underlying surface was introduced in detail. Two parts were contained in this section. First, the time-averaged turbulence equations and turbulence model were presented. Then, the space-average method was used to transform the time-averaged turbulence equations, and new equations which can be used for calculating flow field in vegetation were obtained. The solve method for the control equations was explained.2. Because of the various of leaf area density along the vegetation height, the drag force at different height of the vegetation will be different. The mathematical model mentioned above was used to get the relationship between leaf area density and drag coefficient, and the drag coefficient in additional terms is substituted by function of leaf area density. Then, the flow fields of airflow enter and leave the forest were simulated, the results of wind velocity and turbulence intensity had good agreement with experiment results.3. Leaf area index and stand density are very important characteristics of forest. Aerodynamic roughness length, zero-displacement, and friction velocity of different forests, which have different leaf area index and stand density, were calculated. The variations of aerodynamic roughness length, zero-displacement, and friction velocity with leaf area index and planting density were got. The results of aerodynamic roughness length and zero-displacement show a linear relationship between them. This study is consistent with the results of Shaw & Pereira and Nakai et al.. But the two-dimensional calculation ignores the effect of the trunk, which needs further study.
Keywords/Search Tags:leaf area density, leaf area index, stand density, drag coefficient, flow field around forest, aerodynamic roughness length
PDF Full Text Request
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