Periodic BC in FV

[AdrienWehrle]

Hi everyone,

I'm working on an INSFV app and would need to apply periodic boundary conditions to test it on analytical solutions. I can't seem to find any example of the Periodic Action used in FV, and when I'm trying to add it in [BCs] it's simply being disregarded, (which was somehow expected).

The geometry is a simple 2D block so periodicity should be easy to catch.

Here is my input file: https://github.com/AdrienWehrle/diuca/blob/PR_ViscousFlowFVTests/inputs/viscous_diuca/iceslab_fv_2d_SI_nv.i

I'm on moose-libmesh 2024.12.02 and moose-tools 2024.11.13, and the latest version of moose on master.

Thanks a lot in advance for your help!

[GiudGiud]

Hello

We have only implemented periodic BCs for nodal variables.
For FV, it would be possible to do it through the Functor system:

• create a new object deriving from the FVDirichletBC class
• compute the geometrical transformation from the local face to the face where the value should be the same
• create a functor argument (FaceArg most likely) for that other face
• return the variable_functor(face arg, current state)

This would connect the value on one face to another

[AdrienWehrle]

If I add some 1e-7 sliding in x at the base on the FV setup, it puts everything a bit more in motion but still, the flow induced by gravity should be ~ 5x higher than the sliding. Here it's driving everything...

More importantly, the sliding at the base should be of the same order at the side due to periodicity, but here it decreases..

it seems like the y velocity really shows the slope doesn't do anything, it's really similar to a flow on a flat surface, which shouldn't be the case. As shown in FE.

[AdrienWehrle]

Now trying with periodic velocity on the inclined mesh (with the transform taking the slope of the mesh into account), I still get those near zero velocities with a extremely high viscosity (like 4-5 order of magnitudes above what it should be, which actually makes sense with the extremely low velocities)

[GiudGiud]

and then for FV (on vel_x):

do you have the same kernel for vel_y active?

I think in terms of boundary conditions you should have:

• periodic for vel_x, achieved by setting a dirichletBC on one side equal to the velocity on the other side. (preferably with the BC being upwind, at the higher elevation)
• periodic for vel_y (not sure we need that, but maybe)
• periodic with an offset equal to rho g delta-h between the two sides. That offset is going to be driving the flow, because it's a pressure differential

[AdrienWehrle]

do you have the same kernel for vel_y active?

Yes!

• periodic with an offset equal to rho g delta-h between the two sides. That offset is going to be driving the flow, because it's a pressure differential

this makes me think that might be the one I don't have implemented correctly in FV for now, since pretty much no flow is being created. Interestingly, in FE, I don't have this offset either, but flow occurs and in the right way. This might show a difference between FE and FV? Where FV strictly needs this offset while FE generates it by itself?

[AdrienWehrle]

this makes me think that might be the one I don't have implemented correctly in FV for now, since pretty much no flow is being created. Interestingly, in FE, I don't have this offset either, but flow occurs and in the right way. This might show a difference between FE and FV? Where FV strictly needs this offset while FE generates it by itself?

However this should be resulting in the inclined mesh case, but even with this inclined mesh, flow is not created. Which makes me even more puzzled.