Speaker
Axel Brandenburg
(Nordita)
Description
The turbulent diffusivity tensor is determined for linear
shear flow turbulence using numerical simulations. For
moderately strong shear, the diagonal components are found
to increase quadratically with Peclet and Reynolds numbers
below about 10 and then become constant. The diffusivity
tensor is found to have components proportional to the
symmetric and antisymmetric parts of the velocity gradient
matrix, as well as products of these. All components
decrease with the wave number of the mean field in a
Lorentzian fashion. The components of the diffusivity tensor
are found not to depend significantly on the presence of
helicity in the turbulence. The signs of the leading terms
in the expression for the diffusion tensor are found to be
in good agreement with estimates based on a simple closure
assumption.
