Rotationally induced coherence in turbulent kinematic dynamos


Dallas, V
Tobias, S

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We consider rotating, kinematic dynamos at low magnetic Prandtl number $Pm$.
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 $Rm_c$ is reduced 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
increased by the rotationally induced long-lived large scale eddies with a
coherence time greater than the local turnover time. These eddies play the
major role in determining the dynamo growth-rate.

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Journal Article