Martins Afonso Marco, Mitra Dhrubaditya, Vincenzi Dario
Centro de Matemática (Faculdade de Ciências) da Universidade do Porto, Rua do Campo Alegre 687, Porto 4169-007, Portugal.
Nordita, KTH Royal Institute of Technology and Stockholm University, Stockholm, Sweden.
Proc Math Phys Eng Sci. 2019 Mar;475(2223):20180591. doi: 10.1098/rspa.2018.0591. Epub 2019 Mar 6.
We consider the kinematic fluctuation dynamo problem in a flow that is random, white-in-time, with both solenoidal and potential components. This model is a generalization of the well-studied Kazantsev model. If both the solenoidal and potential parts have the same scaling exponent, then, as the compressibility of the flow increases, the growth rate decreases but remains positive. If the scaling exponents for the solenoidal and potential parts differ, in particular if they correspond to typical Kolmogorov and Burgers values, we again find that an increase in compressibility slows down the growth rate but does not turn it off. The slow down is, however, weaker and the critical magnetic Reynolds number is lower than when both the solenoidal and potential components display the Kolmogorov scaling. Intriguingly, we find that there exist cases, when the potential part is smoother than the solenoidal part, for which an increase in compressibility increases the growth rate. We also find that the critical value of the scaling exponent above which a dynamo is seen is unity irrespective of the compressibility. Finally, we realize that the dimension = 3 is special, as for all other values of the critical exponent is higher and depends on the compressibility.
我们考虑在一种随时间呈白噪声的随机流动中的运动学涨落发电机问题,该流动具有螺线管分量和势分量。这个模型是对经过充分研究的卡赞采夫模型的推广。如果螺线管分量和势分量都具有相同的标度指数,那么随着流动压缩性的增加,增长率会降低但仍保持为正。如果螺线管分量和势分量的标度指数不同,特别是如果它们对应于典型的柯尔莫哥洛夫值和伯格斯值,我们再次发现压缩性的增加会减缓增长率,但不会使其变为零。然而,这种减缓作用较弱,并且临界磁雷诺数低于螺线管分量和势分量都呈现柯尔莫哥洛夫标度时的情况。有趣的是,我们发现存在这样的情况,即当势分量比螺线管分量更平滑时,压缩性的增加会提高增长率。我们还发现,无论压缩性如何,发电机出现时标度指数的临界值都是1。最后,我们认识到三维是特殊的,因为对于所有其他维度值,临界指数更高且依赖于压缩性。