How many geometry domains?
 

I'm wondering what is good practice for relatively complex geometries. If the direction and velocity of flow is very different throughout the geometry, should I split it into a bunch of domains with interfaces so that I can set their initializations seperately? Or should I be keeping it as simple as possible?

Particularly with slow multiphase flows, CFX seemed to have a lot of difficulty producing convincing results if I didn't split it up and set initializations for velocity, direction, and mass or volume fraction seperately.

You don't need to split and join with interfaces just to set initial conditions. Initial conditions can be set on sub-domains, interpolation functions or CEL expressions. The simulation will partition better if it is one domain with no interfaces.

Obviously you need to set realistic initial conditions. This is standard CFD practice.

I will try subdomains again. I think I tried to use them before but I couldn't get them working.