Dynamo action at low magnetic Prandtl numbers: mean flow vs. fully turbulent motion

Yannick Ponty, Pablo Mininni, Jean-François Pinton, Hélène Politano, Annick Pouquet

Published 2006-01-16Version 1

We compute numerically the threshold for dynamo action in Taylor-Green swirling flows. Kinematic calculations, for which the flow field is fixed to its time averaged profile, are compared to dynamical runs for which both the Navier-Stokes and the induction equations are jointly solved. The kinematic instability is found to have two branches, for all explored Reynolds numbers. The dynamical dynamo threshold follows these branches: at low Reynolds number it lies within the low branch while at high kinetic Reynolds number it is close to the high branch.