Robin-Robin FF coupling: mixed boundary conditions for flow coupling

[MakisH]

OpenFOAM provides mixed type boundary conditions, which allow setting both a value and a gradient, essentially enabling Robin-Robin coupling. We already use that in our heat exchanger tutorial, where we read and write sink temperature and heat transfer coefficient.

Supporting such boundary conditions would probably help us improve the accuracy of the coupling (see #93).

[MakisH]

This is not covered by #281

Robin-robin coupling is indeed an interesting additional direction, and it would be different than what we are now doing by reading pressure + gradient of velocity or velocity + gradient of pressure.

Keeping open for now, but nobody is working on this at the moment. We would need a clear use case and some investigation to pick it up.

[precice-bot]

This issue has been mentioned on preCICE Forum on Discourse. There might be relevant details there:

https://precice.discourse.group/t/ff-coupling-with-python-1d-in-house-code-for-flow-distribution/1685/4