Multiphase flow with species transport
 

I am new to CFD and am attempting to quickly learn how to numerically model my physical experiments.

I am attempting to model a saline density current which develops from a lock-exchange mechanism and flows into ambient, fresh water. My 3D domain includes a downstream reach and an upstream reach with an interface connecting the two. Initially, I will have dense, saline in the upstream reach, and fresh water in the downstream reach.

Models in use: VOF, LES, Species.

I have created a material (salt) and have 2 phases (fresh water, and fresh water + salt). That is, my primary phase (fresh water) is only fresh water, and my secondary phase has two species (fresh water and salt).

After initializing my solution, I patch the following:

-volume fraction of secondary phase (saline) to 1 for upstream zone.
-volume fraction of secondary phase to 0 for downstream zone.
-salt mass concentration to 0.035 for the upstram zone.

I would expect from this that the initial density of the upstream zone be greater than that of the downstream zone. However, I find that the initial downstream zone density is correct (998.2 kg/m3), but the upstream zone has a very low initial density which changes if I change the patched mass concentration.

Any ideas of why this may be happening? Any help for this beginner would be greatly appreciated.