Hydrodynamic effects of body-undulation kinematics on thrust production and wake-structure formation in a batoid fish (cownose ray, Rhinoptera bonasus)

• Main Authors: Sen-Hsien Yang, 楊森先
• Other Authors: Jing-Tang Yang
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/83665567062384919825

碩士 === 國立臺灣大學 === 機械工程學研究所 === 100 === This work presents a numerical three-dimension wake-structure of a quasi-steady swimming batoid fish(cownose ray, Rhinoptera bonasus) with constant swimming speed. The three-dimensional, unsteady, viscous and incompressible Navier-Stokes equations were solved with a finite-volume method. A realistic cownose ray body is modeled. Under the condition of zero net forces for an undulation cycle, the performance of thrust coefficient and the transformation of three-dimension flow pattern are reported through alternating the flapping modes of the pectoral fin. Alteration of the body-undulation kinematics was established by varying the undulation amplitudes in both stream-wise and span-wise aspects. Thrust production is found to decrease significantly by 35% when flapping amplitude of leading edge is diminished without changing the span-wise undulation amplitude, fin-tip flapping amplitude and flapping frequency. The fin-tip vortices were found capable of pushing the leading edge vortices back and forth in the span-wise aspect. As the size of the leading edge vortices is diminished by reducing the stream-wise undulation amplitude along the leading edge, the wake-structure formation behind the fish body enforced the pressure difference between snout and tail, this effect further caused the variation of thrust production. This study contained wake-structure visualization and strategy of adjusting thrust performance, it could provide a new maneuvering concept to future underwater vehicle.