[Josh]

Michael's suggestion is correct: poor initial conditions are probably causing this. Alternatively, non-physical boundary conditions could also be the problem. You don't appear to be using any openings (inlets, outlets) so the first option is more likely the problem.

Have you tried solving the simulation with simpler numerical methods? For example, try using a lower-order advection scheme, lower-order turbulence model, lower-order turbulence numerics, etc. If this converges, gradually increase the order of accuracy.