Turbulent dynamo effect and cross helicity in magnetohydrodynamic flows

Abstract

A three-dimensional direct simulation of inhomogeneous magnetohydrodynamic (MHD) turbulence is carried out to investigate the turbulent dynamo effect. The velocity field is driven by an external force so that the velocity and magnetic fields are statistically inhomogeneous in one direction and homogeneous in the other two directions. Several statistical quantities are obtained such as the mean magnetic field, the turbulent energy, and the turbulent electromotive force. The data are used to examine the modeling of the dynamo effect in the four-equation turbulence model. It is shown that the dynamo term related to the cross helicity is more important than the well-known α dynamo term. Some model constants in the four-equation model are estimated using the least-square method.