Add Tutorial: Partitioned multiphase pipe flow

[thesamriel]

This PR adds a tutorial case for the OpenFOAM adapter and its Fluid-Fluid coupling module.

The case consists of a multiphase flow through a 2-D pipe where one half of the inlet provides air, the other half water.
This test case is very basic and unphysical in order to avoid any fluid circulations that usually occur for multiphase flows. Gravity is set to 0.

This case should be run with the alpha-coupling branch of the OpenFOAM adapter. See precice/openfoam-adapter#308

The preCICE files currently still contain (commented out) the coupling of the flux phi. This is to test the coupling of phi from above mentioned PR. However, it serves no purpose to this tutorial and should probably be removed before merging.

I will look into the following ToDos, once we decide if and how we want to keep this tutorial.
TODO:

• Change folder name
• Add Readme
• Remove coupling of phi?
• Check all scripts etc

[MakisH]

Thanks a lot for the PR! I have not yet tested it, but it already looks very clean. I only have some tiny comments.

I will look into the following ToDos, once we decide if and how we want to keep this tutorial.

Well, we have no other case demonstrating two-phase flow, we should keep it. Also as a test case in the system tests. Feel free to mention clearly in the README that this is not a physical case, it has limitations, and it mainly meant as a basic testcase.

Change folder name

partitioned-pipe-two-phase would be good.

Remove coupling of phi?

I am not sure, but some documentation would not harm. If phi is not used at all, it would be confusing to keep it, so let's remove it.

[MakisH]

@thesamriel I can take this over, just let me know if you have any inputs on my previous suggestions.

[thesamriel]

@thesamriel I can take this over, just let me know if you have any inputs on my previous suggestions.

I updated the files according to your suggestions. The only major thing left is the coupling of phi. I left the code in there for you to potentially try it out. However, it is not relevant to this tutorial and should be deleted before merging.

[MakisH]

Just a couple of tiny wrinkles to iron. Thanks a lot, it's almost merged!

[MakisH]

Great work, thank you!
I think this is now ready to merge, as soon as precice/openfoam-adapter#308 is merged.

The notes in the README regarding versions will be updated separately #446.