Dynamo induced by time-periodic force

TL;DR

This paper numerically investigates how the frequency of a time-periodic force influences dynamo action in rotating magnetohydrodynamic flows, revealing resonance effects and nonlinear coupling impacts.

Contribution

It demonstrates the critical role of force frequency near resonance in enabling dynamo action and uncovers the nonlinear interaction between magnetic fields and fluid flow.

Findings

Dynamo action depends on force frequency.

Resonance enhances dynamo ability.

Magnetic energy increases as frequency deviates from resonance.

Abstract

To understand the dynamo driven by time-dependent flow, e.g. turbulence, we investigate numerically the dynamo induced by time-periodic force in rotating magnetohydrodynamic flow and focus on the effect of force frequency on the dynamo action. It is found that the dynamo action depends on the force frequency. When the force frequency is near resonance the force can drive dynamo but when it is far away from resonance dynamo fails. In the frequency range near resonance to support dynamo, the force frequency at resonance induces a weak magnetic field and magnetic energy increases as the force frequency deviates from the resonant frequency. This is opposite to the intuition that a strong flow at resonance will induce a strong field. It is because magnetic field nonlinearly couples with fluid flow in the self-sustained dynamo and changes the resonance of driving force and inertial wave.