Rotationally induced coherence in turbulent kinematic dynamos


Dallas, V
Tobias, S

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We consider rotating, kinematic dynamos at low $Pm$. We show that the
inclusion of rotation leads to an increase in spatio-temporal coherence and a
modification of the turbulent spectrum. These effects make the flow more
efficient in driving the dynamo, in the sense that the energy injection rate
required to reach the critical value of the magnetic Reynolds number $Rm_c$
reduces in comparison with a non-rotating dynamo (Seshasayanan et al. 2017).
For random dynamos it is known that the growth-rate would largely be determined
by the spectral index of the flow at the resistive scale. Here, however, we
demonstrate that the dynamo growth-rate in rotating flows is determined by the
long-lived large scale eddies with a coherence time greater than the local
turnover time.

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Journal Article