  Simulations of stochastically forced shear-flow turbulence in a
shearing-periodic domain are used to study the spontaneous generation of
large-scale flow patterns in the direction perpendicular to the plane of the
shear. Based on an analysis of the resulting large-scale velocity correlations
it is argued that the mechanism behind this phenomenon could be the
mean-vorticity dynamo effect pioneered by Elperin, Kleeorin, and Rogachevskii
in 2003 (Phys. Rev. E 68, 016311). This effect is based on the anisotropy of
the eddy viscosity tensor. One of its components may be able to replenish
cross-stream mean flows by acting upon the streamwise component of the mean
flow. Shear, in turn, closes the loop by acting upon the cross-stream mean flow
to produce stronger streamwise mean flows. The diagonal component of the eddy
viscosity is found to be of the order of the rms turbulent velocity divided by
the wavenumber of the energy-carrying eddies.
