Kinematic dynamo by parity-antisymmetric flows

The paper is devoted to mathematical and numerical modelling of kinematic generation of magnetic feld, involving large spatial scales, by a small-scale flow of incompressible electrically conducting fluid featuring a mirror antisymmetry. Direct numerical simulation demonstrates that such flows can support a magnetic feld generation in presence of two main generation mechanisms, namely, the magnetic alpha-effect and negative eddy diffusivity. The magnetic feld generation can be described as follows: • α-effect creates large-scale feld h0 of amplitude O(1), oscillating on a time scale O("-1). • Fluctuations {h0} of this feld have an amplitude O(1). • Small-scale flow creates {10} with amplitude O("). • Interaction of this feld with small-scale flow creates an electromotive force v × {h1} of amplitude O("). • This electromotive force gives rise to an eddy diffusivity that supports a growth of a mean feld h0 on a time scale O("-1). Here " is the characteristic spatial scale ratio. It may be important for applications that the mechanism for generation considered here does work in a wide range of magnetic Prandtl numbers. Numerical simulation for a flow, which velocity has a zero kinetic helicity everywhere in space, shows that the absence of helicity does not affect magnetic feld generation.