How to find out real moving vortex pressure
 

I have a moving vortex in my unsteady case.
how can estimate its real pressure?is there a rule of thumb for it?
when I refine the mesh the pressure in vortex place reduces in the same time for all meshes.
then,two questions occurs to mind:
1)how can find out the real pressure in the place of vortex?(its core have lower pressure ,right?)
2)how can figure out does it has any major effect on the final preesure and velocity results or doesn't(its not so big in domain)