Numerical Simulation On Sheltering Effect Of Coastal Protective Forest

In order to have a better understanding of sheltering effect of coastal shelter forest system,we simulate the sheltering effect by combining the momentum extraction model proposed byJ.D Wilson and CFD software-FLUENT based on the data of forest community structurecollected from field surveys. Specific forest structure we have simulated in this thesis areforests with different width, mixed types, shrub site. Also, we simulated how did air flow passthrough several Metasequoia glyptostroboides forest shelterbelts. The results showed that:(1) sheltering effects of Metasequoia glyptostroboides forest with different widthThe airflow speed slowly decreased when it is approaching the shelterbelt. But the trendof decreasing is getting faster after4H ahead of the shelterbelt. The reverse flow in theshelterbelt with the width of0.75H appeared further than shelterbelt with the width of2.5H.Moreover, airflow speed behind forest with width of0.75H recovered in a much slower rate theforest with the width of2.5H. Also, the effective sheltering distance of forest with width of0.75H is2H longer than foerst with width of2.5H.(2) sheltering effects of Metasequoia glyptostroboides forest with different communitystructurePerfomance of the airflow in front of the shelterbelt is like other shelterbelts, and thedifference is mainly happened behind the shelterbelt. The reverse flow appeared both in theforest with multiple layers and nonundergrown trees, and the intensity of reverse flow behindthe multiple-layered forest is smaller than forest with nonundergrown trees. Airflow speedbehind multiple-layered forest recovered slower than pure forest, which also means theeffective sheltering distance is longer than pure forest.(3) sheltering effects of Metasequoia glyptostroboides forest with shrub in different siteBecause the height of shrubs is only0.1H, so the sheltering effect of shrubs are limited onthis level. We could find that the airflow speed near the front of forest is almost decreased to0,while the wind speed near the edge of shelterbelt with no shrubs remains the same because ofthe big porosity of lower trunk with no sticks and leaves. Like other types, forest with shrubs both planted in the front and back have reverse flow behind its downward. And the intensity ofthe flow is much stronger when the height is lower. Peak reverse flow behind the forest withfront shrubs is lower than forest with shrubs behind the Metasequoia glyptostroboides forest.Moreover, we also find that forest with shrubs planted in front of it got a higher value in theeffective sheltering distance.(4) Sheltering effects of Metasequoia glyptostroboides forest networkThe turbulence of the airflow is significantly decreased by forest network. We find that thewind speed dreased faster in4H ahead the shelterbelt. What is more, the reverse flow is almostexisted behind every single shelterbelt, and the intensity is not only dominated by the porosityof forest, but also impacted by the vertical height. The reverse flow is much more intensivewhen the porosity is much smaller or approaching the ground. Moreover, we find the effectivesheltering distance in this study is almost10H, therefore we concluded that it is appropriate toset the distance between each shelterbelt as15H.