Speaker
Dr
Nobumitsu Yokoi
(Institute of Industrial Science, University of Tokyo)
Description
Non-vanishing pseudo-scalars in turbulence may give rise to
an effective suppression of enhanced transports due to
turbulence. In the context of dynamo, the turbulent cross
helicity (velocity–magnetic-field correlation in
fluctuations) as well as the turbulent kinetic and/or
current helicty, leads to effective suppression of the
turbulent magnetic diffusivity. This is because, in the
presence of large-scale vortical motions, the positive (or
negative) cross helicity in turbulence should contribute to
the turbulent electromotive force parallel (or antiparallel)
to the large-scale vorticity. One of the key issues is how
and how much the cross helicity can be presented in
turbulence. Possible mechanisms that supply turbulence with
the cross helicity are investigated by considering the
evolution equation of the turbulent cross helicity. Some
recent developments in cross-helicity generation mechanism
using numerical simulations are also presented.
