Numerical Simulation of the Interaction between aFree Falling Circular Cylinder and the Fluid

• Main Authors: Pei-Ju Wang, 王佩如
• Other Authors: Shain-Woei Jeng
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/03171641998907449856

碩士 === 逢甲大學 === 土木及水利工程所 === 92 === Uniform flow past a circular cylinder is a classical fluid dynamic problem. There are two rows of vortices shedding alternatively behind the cylinder at Reynolds number between 40 and 200 which are named Karman vortex street. The periodically vibrating drag and lift forces, induced by the Karman vortex street, have important effect on engineering structures. A primitive-variable method was used to solve for the pressure and the velocity of the flow field of a free falling cylinder. The equation of motion is adopted to compute the motion of the cylinder. After adding artificial disturbances to the flow in the first stage, the constructed model successfully simulates the alternative shedding of the vortex behind a fixed cylinder. In the second stage, the fixed cylinder is released, and the flow field is then interacting with the cylinder. Results show that the cylinder rotates back and forth and moves along a figure of eight path in a coordinate moving with the time-averaged cylinder velocity. The amplitude of the cylinder vibration increases with the inverse of cylinder density and with Reynolds number. The time-averaged drag coefficient decreases with the amplitude of the cylinder vibration. The motion of the free falling cylinder, the evolution of the flow field, the effect of density ratio and the effect of Reynolds number were studied. The dynamic forces, stability of cylinder, fluid damping and two-bubble phenomenon are discussed also.