I need to do some CFD on a system involving multiple droplets of water in flight, including the interactions with the wake of nearby droplets.

It is reasonable to model the droplets as spheres, but The reynolds numbers are around 50, and I need to calculate all the forces on the droplets (including spin-induced Magnus forces) and then propagate the droplet position accurately.

I'll have the financial backing to afford a major commercial package... any reccommendations?

EFD.Lab (see also post further down) can handle particle insertion and trajectory calculations, although it does not account for the spin of the particle. I just checked the documentation of the software (there is a small chapter on this), and it says: "Particles are treated as non-rotating spheres of constant mass and specified (solid or liquid) material."

Do you know anything about the spin ratio, SR = omega * R / V, of these particles. If SR << 1, then the Magnus effect can be neglected. This may very well be the case due to the low Re# (based on particle diameter) flow regime. Do you have any reference on that?

If you would like, I could email you that chapter on particle trajectory calculations from the software documentation (PDF).