cf packing
 

is f-packing related to foam and void in flow?
if it is, how can we do? does flow 3d reduce or change it automatically? or we should change it?
my simulation is very very slow and warns reduce f-packing.
what is the effect of reduced f- packing on result of simulation?

The f-packing algorithm is used to collapse unresolved void regions in the flow. Treat the f-packing warnings as a caution and look to see if the results in that area still make sense. If the results look okay, then don't worry about the messages.

Usually you'll see the f-packing warnings when there is a lot of splashing, which is the more likely the cause of the slow simulation. You can try setting FCLEAN to reduce the splashing or use the implicit velocity threshold to minimize its effect on the run time.