Continuity error in FSI simulation in confined fluid domain

Using preCICE
,
1

Hi,
I am not sure if it is a preCICE-related topic, but my issue appears only when I perform a coupled simulation.
I am trying to simulate something like a plunging airfoil in a confined domain, that is, all the boundaries are defined as walls. I have done a pure OpenFOAM case in which the plunging movement is fixed (using oscillatingDisplacement in the U file), and the simulation runs. As a further step, I attached preCICE to control the movement from another solver.
In this last case, the simulation crashes before connecting to the other solver with an error that appears starting in the adapter, but looks more openFOAM-related:

---[preciceAdapter] Loaded the OpenFOAM-preCICE adapter - v1.3.1.
---[preciceAdapter] Reading preciceDict...
---[precice]  This is preCICE version 3.1.2
---[precice]  Revision info: no-info [git failed to run]
---[precice]  Build type: Release (without debug log)
---[precice]  Configuring preCICE with configuration "./precice-config.xml"
---[precice]  I am participant "Fluid"
---[precice]  Connecting Primary rank to 3 Secondary ranks
--> FOAM Warning : 
    From void adapterInfo(std::string, std::string)
    in file Utilities.C at line 50
    Error (deferred - will exit later) in the preCICE adapter: 

PIMPLE: iteration 1
 --> FOAM FATAL ERROR: (openfoam-2406)
 Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux              : 1e-300
Specified mass inflow   : 3.304020747e-35
Specified mass outflow  : 5.272973784e-35
Adjustable mass outflow : 0

The log mentions a “deferred error” in the adapter, and then the OpenFOAM error appears.
I could probably find a workaround for this but I’d like to understand the origin of the error and if I could do something to overcome it.
Thanks
Claudio

2

Hi Claudio,

This somewhat reminds me of the Master Thesis by Markus Mühlhäusser.
Have a look at the conclusions of the final paragraph on page 77.

https://mediatum.ub.tum.de/1696254

Hope that helps.

Best
Frédéric

3

Hi @fsimonis
thank you for the reference. It’s an interesting aspect, even if in his master thesis Markus deals with fluid-fluid interaction. In this case you need to explicitly exchange some flux.
In my case I’m dealing with FSI in a confined domain, compared to a rigid imposed displacement.
The two fluid setups (0 folders) are identical, apart from the definition of the pointDisplacement at the wet surface.
It might be that, while coupling with preCICE and an external solver, if the solid deforms “a bit” (expands or shrinks due to the coupling) the fluid domain changes the overall volume and, being incompressible, shows a continuity error. When the solid movement is rigid (directly computed in OpenFOAM) the error is avoided. It is just my guess at the moment.

(a side note, the preCICE error that I mentioned before was unrelated, I had a typo in my preciceDIct).

Claudio