| Summary: | 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.
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