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標題: 撓性尾鰭下游之流場結構與推力之實驗探討
Experimental Study on Flow Characteristics and Thrust of Flexible Oscillating Fin
作者: 謝偉麟
Hsieh, Wei-Lin
關鍵字: flexible fin;可撓性魚鰭;rigid fin;thrust;efficiency;reversed Karman vortex street;硬式魚鰭;推力;效率;逆卡門渦列
出版社: 機械工程學系所
引用: 參考文獻 1. J.-M. Miao , M.-H. Ho , “Effect of flexure on aerodynamic propulsive efficiency of flapping flexible airfoil”, Journal of Fluids and Structures , Vol.22 , pp. 401-419 , 2006 2. K. Taylor , L. Nudds , L. R. Thomas , “Flying and swimming animals cruise at a Strouhal number tuned for high power efficiency”, NATURE , Vol.425 , pp. 707-711 , 2003 3. O. M. Griffin , M. S. Hall , “Review-vortex Shedding Lock-on and Flow Control in Bluff Body Wakes” , Journal of Fluids Engineering , Vol.113 , pp. 526-537 , 1991 4. 丁上杰 , “魚類操控式游動之流體物理與仿生學研究”, 國立清華大學 , 動力機械工程學系博士論文, 2009 5. J. Young , C.S. Lai , “Mechanisms Influencing the Efficiency of Oscillating Airfoil Propulsion” , AIAA Journal , Vol. 45 , No. 7 , pp. 1695-1702 , July 2007 6. J. C. S. Lai , M. F. Platzer , “Jet Characteristics of a Plunging Airfoil” , AIAA Journal , Vol.37 , No.12 , pp.1529-1537 , December 1999 7. R. Müller, A. Oyama, K. Fujii, H. Hoeijmakers,“Propulsion by an Oscillating Thin Airfoil at Low Reynolds Number”, JAXA Institute of Space and Astronautical Science , 2008 8. J. Young and J. C. S. Lai ,“Vortex Lock-In Phenomenon in the Wake of a Plunging Airfoil”, AIAA Journal , Vol.45 , No.2 , pp. 485-490 , February 2007 9. W. Gu, C. Chyu, and D. Rockwell ,“Timing of vortex formation from an oscillating cylinder”, Phys. Fluids 6 (11) , pp.3677-3682 , November 1994 10. Y. Lian and W. Shyy ,“Laminar-Turbulent Transition of a Low Reynolds Number Rigid or Flexible Airfoil”, AIAA Journal , Vol.45 , No.7 , pp.1501-1513 , July 2007 11. S. Heathcote and I. Gursul ,“Jet switching phenomenon for a periodically plunging airfoil”, Physics of Fluids , Vol.19 , 027104-1~027104-12 , February 2007 12. H. Dong , R. Mittal , M. Bozkurttas and F. Najjar ,“Wake Structure and Performance of Finite Aspect-Ratio Flapping Foils”, AIAA Journal , 2005-0081
本論文的目的是研究搖擺魚鰭附近及下游的流場結構、推力與效率等特性。實驗之魚鰭分為可撓性與硬式兩種。在以入流速為5 cm/s(相當於雷諾數等於1000)、旋轉振幅為±10°、魚尾鰭長度為7cm以及擺動頻率介於0.4至1.5Hz的情況下,當史卓荷數大於0.192,魚尾前渦漩領先魚尾後渦漩,此時尾流結構為卡門渦列,且推力為負值。當史卓荷數大於0.243時,在週期擺動過程中,尾流呈現逆卡門渦列的形式,且推力變成正值。當史卓荷數介於0.243~0.292時,魚尾前渦漩與魚尾後渦漩在魚尾鰭後緣同時結合。當史卓荷數增加至0.34~0.486時,魚尾後渦漩領先魚尾前渦漩。此時,兩個渦漩的結合並不是很完整,呈現兩個渦漩分散的逆卡門渦列。當史卓荷數大於0.438時,魚尾前渦漩的結構被魚尾鰭所破壞,下游處只見魚尾後渦漩。本文中,可撓性魚鰭在史卓荷數等於0.34擁有最高的效率,約為30.6%;而硬式魚鰭則在史卓荷數等於0.389擁有最高的效率,約為26.2%。當史卓荷數小於0.4時,可撓性魚鰭的效率高於硬式魚鰭的效率;當史卓荷數大於0.4時,可撓性魚鰭與硬式魚鰭效率均開始下降,且可撓性魚鰭的效率低於硬式魚鰭的效率。

This study investigates the flow structures behind of an oscillating fin, the thrust force and propulsive efficiency by experiment. One rigid and one flexible fin are employed. The Reynolds number, based on the oscillating amplitude, is about 1000. The length of fin is 7 cm, the oscillating amplitude is and the oscillating frequency ranges from 0.4 Hz to 1.5 Hz. For both fins, while the Struohal number is smaller than 0.192, the leading vortex leads the trailing vortex. In such cases, the wake flow structure is the traditional Karman vortex street and the thrust is negative. As the Strouhal number is greater than 0.243, the wake shows the reversed Karman vortex street and the thrust force becomes positive during the oscillating cycle. As the Strouhal number ranges between 0.243 and 0.292, the leading and trailing vortices synchronously combine together near the trailing edge of the oscillating fin. As the Strouhal number increases from 0.34 to 0.486, the trailing edge vortex leads the leading edge vortex. During the evolution process, synchronization of these two vortices is not perfect; and they combine as a large scale reversed vortex street with diffused appearance. At even higher Strouhal number, leading edge vortex is destroyed near the trailing edge by the oscillating fin. In such cases, only the trailing vortices are shed downstream in form of a reversed Karman vortex street. The maximum propulsive efficiency for the flexible fin is about 30.6% at Strouhal number 0.34; and that for the rigid fin is about 26.2% at Strouhal number of 0.389. The reversed Karman vortex street is formed at relatively smaller Strouhal number for the flexible fin than for the rigid fin. For Strouhal number smaller than 0.4, the efficiency is higher for the flexible fin than for the rigid one; and vice versa for Strouhal number greater than 0.4.
其他識別: U0005-2508201016191800
Appears in Collections:機械工程學系所

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