Dynamics of the decay of an isolated sphere of turbulence*

We perform direct numerical simulation and large eddy simulation of an initially spherical region of turbulence evolving in free space.  The computations are preformed with a lattice Green’s function method, which allows the exact free-space boundary conditions to be imposed on a compact vortical region. The initial condition is spherically windowed, forced, isotropic turbulence.  We study the statistics of the decaying region of turbulence as a function of radius and time.  The boundary develops intermittency and features occasional ejections of vortex rings.