Numerical Simuiation of Kármán vortex streets

• Main Authors: Hurng, Muh-Jyuu, 洪木舉
• Other Authors: Tsai, Chung-Tien
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/71841205917517970692

碩士 === 國立屏東科技大學 === 機械工程系 === 90 === Abstract Fluid flows passing obstacles are common in engineering applications. They generate Von Kármán vortex streets for Reynolds number roughly between 40 and 300. The frequencies of the vortex streets are critical importance in the structure’s safety. In the study Cosmos’s FlowPlus is applied to numerically simulate fluid flows passing circular cylinders. We analyzed the frequencies of the vortex streets. Results show that the frequencies can be read directly from average-flow-velocity diagram, creating automatically by FlowPlus, for a circular cylinder. Some cases for two circular cylinders are also studied. Because the gap ratio（G/D）will affect the flow, wake flows behind the respective cylinders interfere with each other. The flow fields show drastic difference in the numerical results; therefore the frequencies of flows are more difficult to get. We try many ways, we finally choose an observation point far behind cylinders in the vortex path and record the velocities in the streamline and perpendicular directions. Then Fast Fourier Transform (FFT) is applied to find frequencies; the commercial software, Tecplot, is used to plot the spectra. Comparing with experimental data from former researchers, our numerical results show errors within 10 percents. As the result, the direct numerical simulations by FlowPlus can be used to find vortex’s releasing frequencies for two circular cylinders within reasonable accuracies.