仿生可撓性翼在高效率史徹赫數下的流場分析

Abstract

本實驗是研究以NACA0012可撓性翼為主體，並在以水為工作流體的流場下，作周期性的擺尾動作，並配合周期性的昇降運動及定速的拖曳運動，並觀察其在可撓性翼尾端(Trailing edge)所產生的渦漩及流場行為，另外在流場外、拖曳平台的側邊，設置一CCD高速攝影機，用以拍攝流場，且設定和可撓性翼作同步昇降運動。 其中昇降運動的角頻率、拖曳運動的行進速度皆為控制變因，為固定值不變，其中昇降角頻率為配合史徹赫數為0.1時而設定，對應之角頻率為0.49 rad/s；拖曳運動的行進速度為配合雷諾數為8000而設定，其對應之行進速度為5 cm/s ；而擺尾角頻率為以史徹赫數0.1為基底，每0.05作一次觀察，直到史徹赫數至0.45，這其中包括了水中生物最佳效率之史徹赫數範圍。 將實驗數據利用PTV(Particle Tracking Velocity)粒子軌跡測速法做分析，實驗結果發現，當史徹赫數在0.2~0.35之間(即一般生物最佳巡弋效率下)，流場渦流結構不僅完整且集中，渦度值也夠強，所產生的噴流速度及方向，相對於其他史徹赫數亦是最佳；另外當相位角相差180度時，由於昇降與擺動的相對運動，更加強其渦度值，且渦流結構更集中，比較不會散溢，噴流速度亦是最大。

The experiment based on NACA0012 flexible airfoil was to explore the periodical heave, pitch and steady towing velocity in a free surface container of still water. The behavior of flow field and the vortices behind the Trailing edge were observed by CCD synchronized with heave. The heave angular frequency was adjusted to St = 0.1 (ω1 = 0.49 rad/s), and the towing velocity was adjusted to Re = 8000 (U = 5cm/s). The pitch angular frequency was investigated in 0.05 increments (Max. 0.45). The experiment data was analyzed by PTV (Particle Tracking Velocimetry). According to the results, the phenomena of strong and concentrated vortices and the perfect jet between optimal St (0.2~0.35) were found. The opposite motion between heave and pitch (phase angle equals to 1800) strengthened the vorticity and concentrated the structure.