- 學位論文
鈍體後方渦旋與魚身擺動間相位對流場之影響
Effect of Phase between The Vortex Shedding and The Field Swimming upon The Flow Field
摘要
本研究主要透過計算流體力學軟體(ANSYS-FLUENT)模擬三維流場中阻礙物後方的魚隻擺動，探討魚在圓柱後方尾流區游動時與逸散渦流間之互動關係。文章中，固定圓柱與魚隻之間距(0.2m)，讓魚隻在流場速度0.9m/s之自由流中游動，魚隻擺動周期為0.45秒，以1/6週期(0.075秒)為一個單位，並施以六種延遲，觀察其流場特性及觀察游動功率變化。 研究結果顯示，在 (0.000秒、0.075秒、0.150秒、0.225秒、0.300秒、0.375秒) 等六個不同之起始擺動時間點下， (0.075秒、0.225秒、0.300秒、0.375秒)等起始擺動時間點有較小之游動功率，而0.000秒及0.150秒等之起始擺動時間點有較大之游動功率。由壓力圖得知，前三個時間點(0.000s,0.075s,0.150s)之壓力分佈圖趨勢較為類似，但0.075秒之壓力數值較另外兩個時間點小了許多，反而與0.225秒、0.300秒、0.375秒之壓力數據較接近。其原因推測為魚隻前方渦漩與魚尾渦漩相互抵消，且魚隻擺動時高壓區位於擺動方向另一側。
並列摘要
This research simulated the characteristics of the flow field with an undulating fish behind a blunt body in three-dimension. A CFD software (ANSYS-FLUENT) was used to analyze the interaction of flow field induced by the vortex behind a blunt body and the vertical flow initiated by an undulating fish. Parameters included in this study were, the velocity of the fish swimming (0.4m / s), the distance between the blunt body and the fish (0.2m), the undulating period of swimming (0.45s). One sixth period of increment was used in analyzing the effect of various delay offset on the characteristics of the flow field and the variation of power required for swimming. The results show that in six different starting undulating delays (0.000s, 0.075s, 0.150s, 0.225s, 0.300s, 0.375s) , the following four cases (0.075s, 0.225s, 0.300s, 0.375s) showed smaller swimming power required, while the other two (0.000s, 0.150s) needed higher swimming power. Results indicated that the first three cases exhibiting similar trend in pressure variations. However, the pressure variation of the case with delay of 0.075 was milder than the other two. Similar results were also observed in second group. It could be caused by the cancelling of vortex on one side of fish and the high pressure on the other side.