How to bake multiple fluid simulations in one scene?

Question

If we understood correctly, Blender does not allow more than one domain for fluid simulation in a given scene. This means that any inflow (fluid) object will be transformed into only one domain object as the final simulated fluid. That is, regardless to any material assigned to inflow (fluid) objects, ultimately the domain material will apply. This causes difficulties to experience mixing fluids as questioned here.

In our recent trial in the following figures in order to simulate two different types of fluid (i.e., different material, etc) we simulated each separately and baked. Now we question how we can use the resulting images to put the fluids together in one animation? We tried to composite but didn't get acceptable results. Is this the correct approach or is it possible to bake multiple simulations in a scene?

Note that before we end up with separate baking we played sometime with multiple scenes, different layers but no success in putting two fluids together!

Answer 1

Here we share our results based on the method explained {here} and {here}.

The idea is simple:

1) define domain, fluid, obstacle etc
2) assign unique folder for baking cache
3) bake the fluid one
4) remove domain and fluid associations

Repeat the above as many times you want (here in the following example we did it three times). Trick: Indeed, for the following example we just baked once. Then we copied domain+obstacle two times. Relocated them on the scene. Duplicated all the cache on the disk two times in two folders that later we assigned in the above algorithm :))

We also used offset frame just to make the fluids a little bit different in stage:)

Note: domains can overlap or whatever, but notice that the fluids do not interact each other but overlay.

Answer 2

If you want multiple fluid sims create the first sim and bake it having specified a directory to cache. Now remove the fluid domain modifier from the first cube. Create your second sim, specify a new cache directory and bake. Repeat, disabling each domain except the one you are baking. You can set parameters different for each sim. When you have all 4 sims baked, go back and re-enable the Domain status so all four domains exist and be sure to specify which directory they will read from. To start them at different times, adjust the offset. To delay 100 frames, set the offset to -100. The fluids won't interact, but you can have them all running at once, you just can't bake them all with more than one domain present.