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摘要
The interactions of two like-signed vortices in viscous fluid are investigated using two-dimensional numerical simulations performed across a range of vortex strength ratios, Lambda = Gamma(1)/Gamma(2) <= 1, corresponding to vortices of circulation, Gamma(i), with differing initial size and/or peak vorticity. In all cases, the vortices evolve by viscous diffusion before undergoing a primary convective interaction, which ultimately results in a single vortex. The post-interaction vortex is quantitatively evaluated in terms of an enhancement factor, epsilon = Gamma(end)/Gamma(2,start), which compares its circulation, Gamma(end), to that of the stronger starting vortex, Gamma(2,start). Results are effectively characterized by a mutuality parameter, MP = (S/omega)(1)/(S/omega)(2), where the ratio of induced strain rate, S, to peak vorticity, omega, for each vortex, (S/omega)(i), is found to have a critical value, (S/omega)(cr) approximate to 0.135, above which core detrainment occurs. If MP is sufficiently close to unity, both vortices detrain and a two-way mutual entrainment process leads to epsilon > 1, i.e. merger. In asymmetric interactions and mergers, generally one vortex dominates; the weak/no/strong vortex winner regimes correspond to MP <, =, >1, respectively. As MP deviates from unity, decreases until a critical value, MPcr is reached, beyond which there is only a one-way interaction; one vortex detrains and is destroyed by the other, which dominates and survives. There is no entrainment and epsilon similar to 1, i.e. only a straining out occurs. Although (S/omega)(cr) appears to be independent of Reynolds number, MPcr shows a dependence. Comparisons are made with available experimental data from Meunier (2001, PhD thesis, UniversitE de Provence-Aix-Marseille I).
- 出版日期2017-10
