Continuity not converging
 

I'm running a transient simulation of hydrogen dispersion behind a cubical building. I'm using PISO with 30 corrector stages (implicit scheme) with a time step of 0.1sec. The log file shows me that every few time steps the continuity equation does not converge which takes the iterations up to the 30 corrector stages; therefore increasing my solution time.

Does anybody have any advise on how to get it to converge such that I can save some time?

All comments are greatly appreciated:

Specs: STAR-CD

•Inlet at west 7/ms k=0.01m2/s2 e=0.0002m2/s3 and a tempertaure profile (on Z) of -1°/100m

•Outlet at east split = 1

•Ground soft surface E=9

•Rest; symetry boundaries

•Domain 750m L 350m W 250m H

•cube (60m) center at x = 380m

Hector A. Olvera