Relaxation in two dimensions and the ‘‘sinh‐Poisson’’ equation

Long‐time states of a turbulent, decaying, two‐dimensional, Navier–Stokes flow are shown numerically to relax toward maximum‐entropy configurations, as defined by the ‘‘sinh‐Poisson’’ equation. The large‐scale Reynolds number is about 14 000, the spatial resolution is (512)2, the boundary conditions are spatially periodic, and the evolution takes place over nearly 400 large‐scale eddy‐turnover times.