| Summary: | 碩士 === 逢甲大學 === 水利工程所 === 95 === A flow past a rotationally oscillating circular cylinder is studied by a numerical model. The main non-dimensional parameters are Reynolds number, Re, amplitude of oscillation, , and frequency ratio , where represents the frequency of oscillating cylinder, and is the natural frequency of vortex shedding. The ranges considered are , , and . The purpose of this paper is to discuss the effect of these non-dimensional parameters on the flow field. Two-dimensional incompressible Navier-Stokes equations are solved by primitive-variable method. According to the characteristic of the shedding vortices, the frequencies of the oscillating cylinder could be divided into lock-on, buffer, and unaffected regions. In the lock-on region, the shedding vortex was strengthened. In the buffer region, the vortex was weakened. As Reynolds number and amplitude of oscillating increased, the energy, the pressure, and the vorticity of the vortices increased. As the amplitude increased, the lock-on region increased, the minimum of the vortex energy dropped, the peaks of the drag, the lift, and the vortex energy increased, and all the respective frequencies of the minimum and the peaks decreased. When the amplitude is lower than about 2°, the lock-on region shrunk to a line, i.e..
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