Decaying two-dimensional turbulence in a circular container

We present direct numerical simulation of two-dimensional decaying turbulence in a circular container with no--slip boundary conditions. Starting with random initial conditions the flow rapidly exhibits a self--organization into coherent vortices. We study their formation and the role of the viscous boundary layer on the production and decay of integral quantities. The no--slip wall produces vortices which are injected into the bulk flow. The self-organisation of the flow is reflected by the transition of the initially Gaussian vorticity probability density function (PDF) towards a distribution with exponential tails. Due to the presence of coherent vortices the pressure PDFs become strongly skewed with exponential tails for negative values.