The Study of Using Corrected Core Spreading Vortex Method for Simulating The Merging Process of Co-ratating Vortices

• Main Authors: Shou-Te Chen, 陳壽德
• Other Authors: 黃美嬌
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/88399417119641602092

碩士 === 國立臺灣大學 === 機械工程學研究所 === 94 === Simulations for a pair of equal-strength co-rotating vortices in use of improved core spreading vortex method is discussing in the thesis. The core spreading vortex methods generally have the problem of no correct convergence to the Navier-Stokes equations. To be correct, the core size of simulated vortex elements cannot be too large. The technique of splitting a fat vortex element into some thin ones in order to fix the convergence problem is convenient and efficient. In particular, it keeps the method purely Lagrangian. A new splitting method in which several weaker child vortices surround a thinned but still strong parent vortex is proposed. The computational amount on the other hand is kept reasonably large by merging similar and close-by vortices. According to previous experiment research, it is found that complete merging undergoes four stages with physical meaning. The second (convective) stage represents the heart of the vortex merging process. The vortices become markedly deformed, and closer. It is also found that the time required for merging is inversely proportional to the square root of the Reynolds number. If one observes the streamlines in a rotating reference frame(observer moves with the vortices), then one finds the central saddle point vanishes, despite the fact that the vorticity still has two distinct peaks and mergers is not complete. We think that it is concerned with the rotating speed of the observer. Eventually, we try to find out the relationship between the rotating speed of the observer and the streamline patterns.