| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 94 === The purpose of this study is to numerically investigate how the various intervals of the two-section windbreak fences will affect the flow of wind around it and set a simulation mode. In order to ensure the accuracy of the numerical simulation, this study employed 2 scaled models for wind tunnel experiments. The fences had a height (H) of 9cm and sectionalized into 2 sections with 4.5cm of height. In addition, the wind tunnel experiment is to use a method of testing and verifying the differences in numerical simulation. In each test, 30% of the windbreak fences will allow ventilation, and we have simulated the test with the Reynolds number (7.2×104 ), the thickness of the boundary layer ( 5.33H ), and the n index of the Power Law (0.157).After handling and analyzing the data of the test with the software, we then proved the mode is applicable by confirming and verifying the results. Moreover, seven sets of research cases were chosen to test the numerical simulation to study the impact of flow variation on windbreak effect.
The conclusions of this study are:
1. The difference between two-section type of windbreak and the tradition vertical type depends on the shape variation. The air flow through the upper half grid will be further raised by the air flow through the lower half grid. That will consequently widen the range of low wind speed area, thus will achieve the windbreak effect.
2. The windbreak effect of various intervals of the two-section windbreak fence: In case of the interval of two-section type of windbreak increases, the low wind speed zone in lee side becomes longer, which will increase the protection distance and the windbreak effect near the earth surface. In this study, when the interval equals to 2H, the protection distance reaches its maximum value, which is 1.48 times longer than that of the single windbreak grid. As the interval decrease to H/3, the more the rising air flowing through the lower half grid, the less the air passing through the construction, the reflux area of down-stream is the largest with the best windbreak effect, while the protection index (P.I.) is 1.18 times than that of the single wind-break grid.
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