Mechanism of the Lift for a Rotationally Oscillating Cylinder

• Main Authors: Yung-lin Liu, 劉勇麟
• Other Authors: Shain-Woei Jeng
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/03399379054226236543

碩士 === 逢甲大學 === 水利工程與資源保育研究所 === 96 === The lift of the flow past a rationally oscillating circular cylinder is studied by numerical model. A Primitive method is used to solve the Navier-Stokes equations for the flow field. First, method of vortex observation were studied, according to the process of the vortices shedding. Second, changed the cylinder rotation frequency, and observed how it affected the strength, the formation, and process of vortices, thus affected the pressure distribution on cylinder surface, and final affected the lift. After comparing the streamline, pressure, and vorticity figures, it was found that the bubble of the streamline figure was not a suitable representation for attached vortex. Absolute pressure figure was good for observing the process of the vortex shedding. Pressure of the vortex center accumulated up to peak and then decayed. The peak was higher at higher rotational frequency of the cylinder in the lock-on region. The center of the vortex first approached the center line in flow direction, and then left the center line. The longitudinal distance between two consecutive vortices gradually became bigger, and then reached a constant. This distance was inversely proportional to the rotational frequency. The higher the frequency, the higher the absolute pressure value of the vortex center.