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標題: | 邊牆對等速球所受形狀阻力及壓力場之影響 Influence of adjacent walls on the form drag and pressure field of a constantly moving immersed solid sphere |
作者: | Jia-Chi Chang 張嘉棋 |
指導教授: | 沈弘俊 |
共同指導教授: | 楊馥菱 |
關鍵字: | 低雷諾數,邊壁效應,影響距離,形狀阻力,PIV 實驗, low Reynolds number,wall effect,influence distance,form drag,PIV, |
出版年 : | 2013 |
學位: | 碩士 |
摘要: | This thesis experimentally investigates the influence of adjacent walls on the flow field around an immersed solid sphere when the two solid surfaces approach constantly at low Reynolds number (Re=0~50). When an upstream wall approaches the sphere, it squeezes the liquid between the two surfaces can cause changes, known as the “wall effects”, in the flow dynamics when the wall is far away. The wall effect includes rise in the flow velocity and pressure filed in the interstitial gap, augmentation of the surface pressure distribution that in turn gives a higher form drag. In this experiment, a steel sphere is fixed in the middle of a constantly-rising water tank filled with glycerol-water mixture. We used different tank velocity to achieve flows at different Reynolds numbers, Re. The flow field is monitored by the technique of PIV. When the wall is close enough to modify the flow field, we use the interstitial gap between the wall and the sphere to define an “influence distance”. We further use the rise of the form drag to quantify this influence distance to study how it varies with Re. In addition, we also moved the sphere to an eccentric position closer to a tank side-wall to examine the side-wall influence on flow field and the influence distance of the upstream wall.
The results show that the influence distance decreases monotonically with Re when Re<20 but it asymptotes to a constant value about 0.5 diameter(D) when Re≧20.With a nearby lateral wall at 2D away, the trend remains nearly identical when Re≦20 but gives a higher influence distance, by 0.1D, from that without the lateral wall. This is because the additional wall has stronger decelerating effect on the interstitial liquid motion at higher Re. The same constant influence distance is found for Re≧20 when the lateral wall is moved to an even smaller lateral distance 1D; however, a smaller value is obtained at Re=5 and 10. This error is attributed an induced local flow by natural convection when the liquid is consistently heated by the PIV laser. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/61214 |
全文授權: | 有償授權 |
顯示於系所單位: | 應用力學研究所 |
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