SimScale CAE Forum

Multiphase simulation of water rocket error: "Multiphase domain needs exactly two materials..."


I’m currently working on a multiphase simulation of a water bottle rocket launch. The air is 5bar overpressure over the water, at the beginning.

The idea is that the simulation will show how the water is vented through the nozzle until it gets empty and the air pressure gets 0 in the bottle too.

However I face the following error message when I start to run the simulation:

Here is the link to the project.

I’d like to get something similar to this but with water-air interaction:

Any suggestion is welcome!
Thank you in advance! :slight_smile:


Note to myself: always read the documentation regarding the topic before opening a new thread…
This link below explained what I did wrong:


The associated phase of ‘Phase 0’ means that the fluid material will be the primary fluid phase. This is then represented by a ‘Phase fraction’ of value 0 that corresponding to 100% of this fluid. Further, Every fluid material must be assigned at least 1 volume (and vice-versa).


At this stage, we are only defining the properties of the two fluid materials that will be present in the domain/mesh and assigning them to the corresponding mesh volume (in this case the same one). As for the initial distribution of the fluid materials, it will be defined later under “Initial Conditions” sub-tree entry (under “Model”) with the help of “Geometry Primitives”.


This is a good topic as I for one, am guilty of the same thing a lot of the time… But some things are just not obvious when we try to expand our knowledge base :wink:

I would likely have found this topic before I would have found the Tutorial for the answer, now when I got here, I could have gone to the tutorial that I had not found yet :slight_smile:

Don’t forget to mark Post 2 as the answer…