  We perform direct numerical simulation (DNS) and large eddy simulation (LES)
of an initially spherical region of turbulence evolving in free space. The
computations are performed with a lattice Green's function method, which allows
the exact free-space boundary conditions to be imposed on a compact vortical
region. LES simulations are conducted with the stretched vortex sub-grid stress
model. The initial condition is spherically windowed, isotropic homogeneous
incompressible turbulence. We study the spectrum and statistics of the decaying
turbulence and compare the results with decaying isotropic turbulence,
including cases representing different low wavenumber behavior of the energy
spectrum (i.e. k^2 versus k^4). At late times the turbulent sphere expands with
both mean radius and integral scale showing similar time-wise growth exponents.
The low wavenumber behavior has little effect on the inertial scales, and we
find that decay rates follow Saffman (1967) predictions in both cases, at least
until about 400 initial eddy turnover times. The boundary of the spherical
region develops intermittency and features ejections of vortex rings. These are
shown to occur at the integral scale of the initial turbulence field and are
hypothesized to occur due to a local imbalance of impulse on this scale.
