Volume-coupled flow tutorial

[tirgendetwas]

Tutorial to validate volume coupling on a mesh region and the reading of internal fields in OpenFOAM. Flow is introduced into the system through a square region of cells. The dummy participant writes Velocity at a constant value, the fluid participant reads that value on a cellSet and enforces it through fvOptions.

This tutorial could be a basis for a more complex scenario where the dummy solver is replaced or expanded.

TODO:

• README.md

[MakisH]

Some first comments for the next iteration. Keep it rolling!

[MakisH]

Status: This case currently stumbles upon this preCICE assertion on the Nutils side:

---[precice]  iteration: 1, time-window: 201, time: 1 of 4, time-window-size: 0.005, max-time-step-siz
e: 0.005, ongoing: yes, time-window-complete: yes, 
ASSERTION FAILED
Location:   void precice::cplscheme::BaseCouplingScheme::sendData(const PtrM2N&, const DataMap&, bool)
File:       /home/gc/repos/precice/precice/src/cplscheme/BaseCouplingScheme.cpp:119
Expression: math::equals(timesAscending(nTimeSteps - 1), time::Storage::WINDOW_END)
Rank:       0
Arguments:  
  0: timesAscending(nTimeSteps - 1) == 0.9999999999999787
  1: nTimeSteps == 2

which is discussed in precice/precice#1751.

Since:

• The case was previously running correctly with preCICE v2.5.0
• The results we obtain till it hangs (at t=0.35) look reasonable
• It could be a test case to evaluate if the original issue is resolved (@BenjaminRodenberg)

I suggest merging this already.