I have run several simulations of nitrogen gas flow over - what looks very much like an engine exhaust valve.  I ran several versions of the valve with increasing tail cones to reduce drag.  All of the results for pressure across the body are nearly the same, and no turbulence or vortices are shown behind the body in the trajectory results.  The velocities approach 500 ft/sec, so the flow is not laminar.  I have set the turbulence "number" at 5%.  How should theis problem be setup to give more realistic result?