Dynamic vortex lattice state in active fluid model

A generalized Navier Stokes equation has recently been proposed to model turbulent dynamics in active fluids (Wensink et al., PNAS 2012). In the regime of strong nonlinear advection, this system relaxes to a novel dynamic vortex lattice state. This video shows the formation of this dynamic hexagonal vortex lattice from random initial conditions. The simulation was conducted by using a pseudospectral algorithm on a 1024x1024 grid with a time step of 0.002.
See arxiv.org/abs/1711.10865

[@ahorfandinn]

Thank you for the video! Is there any reason why the lattice is formed by posivite (yellow) vortices and not the negative ones?

[@michaelwilczek8676]

This is called a spontaneous symmetry breaking. If you repeat the simulation many times with different initial conditions, you will find positive vortices in one half of the cases and negative vortices in the other half.