Pointwise vanishing velocity helicity of a flow does not preclude magnetic field generation

Phys Rev E. 2019 Mar;99(3-1):033204. doi: 10.1103/PhysRevE.99.033204.

Abstract

Pointwise zero velocity helicity density is shown not to prevent steady flows from acting as kinematic dynamos. We present numerical evidences that such flows can generate both small-scale magnetic fields as well as, by the magnetic α-effect or negative eddy diffusivity mechanisms, large-scale ones. The flows are constructed as curls of analytically defined space-periodic steady solenoidal flows, whose vorticity helicity (i.e., kinetic helicity) density is everywhere zero.