The Study of Using Corrected Core Spreading Vortex Method for Simulating The Merging Process of Co-ratating Vortices
Date Issued
2005
Date
2005
Author(s)
Chen, Shou-Te
DOI
zh-TW
Abstract
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.
Subjects
渦漩法
渦泡分裂
渦泡融合
共轉渦漩
Vortex Method
Core Spreading
Vortex Splitting
Vortex Merging
Co-rotating Vortices
Type
thesis
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