#93 Checker board effect with pimpleFoam and interfaceTracking

[Iason Tsiapkinis]

Hello, I have encountered an issue with interfaceTracking. This issue persist for different Openfoam versions (2312, 2412) and also the foam-extend-4.1 and 5.0 version of interfaceTracking. I have posted the issues in the openfoam gitlab. Attached you will find a case-setup for a liquid column in foam-extend-5.0.
https://develop.openfoam.com/Development/openfoam/-/issues/3320

The library interfaceTrackingFvMesh produces wrong fluxes through the interface when adding gravity, resulting in a checkerboard flow.
This makes the library unusable when simulating a liquid bridge or a drop in 2D and in 2D axisymmetric.

I have spend a considarable amount searching for the issue. The effect is visible, even when turning rigidSurface, i.e. no moving interface.
- Both boundary conditions (freeSurfacePressure and freeSurfaceVelocity) produce this effect. The influence of the pressure boundary condition is higher
- changing the motion direction to normalMotionDir does not help
- any other correction available in the library does not help
- The image shows the cnoverged result, i.e. there is no residual mesh movement
- the effect is there for 2D or 2D axisymmetric (wedge) cases
- I tried many different schemes with similar results
- The contact angle boundary condition has no influence
- This issue persist for foam-extend 4.1 and openfoam versions 2112, 2212 and 2312
- This issue pesist when simulating two fluids

[Iason Tsiapkinis]

This is the resulting pressure field, clearly exhibiting checkerboard effect. This probably comes from a discontinoous shape of the free surface, resulting in a alternating fsNetPhi field.
Checkboard effect is reduced with free free surface patches, but is still noticable.