Abstract
The existence of new chiral non-linearities in the large-scale dynamics of 2D incompressible Navier-Stokes flows subject to suitable small-scale forcing is discussed. The force is random, homogeneous and isotropic or deterministic, space-time periodic and invariant under π/3 rotations, but not mirror-symmetric. When the large-scale vorticity and stream function are functionally related, the usual non-linearity vanishes, but the chiral non-linearity does not in general, and can lead to strong enhancement or depletion of large-scale vortices depending on their cyclonicity. For parallel flow, the non-linearity is that of Burgers' equation.