[aerosayan]

Face normals on cartesian grids are constant for every cell.
When we coarsen the grid for a multigrid solver, we don't have to worry about calculating new face normals for the coarsened cartesian grids.


But for non-cartesian grids (as shown in fig), the face normals aren't constant for every cell.


I want to use Geometric Multigrid for an explicit FVM solver for the mesh shown in fig.


- When I coarsen the grid, do I have to worry about what will be the new face normals of the coarsened grid?
- If I do have to worry about them, can I just average the face normals from the fine grid to the coarse grid?

Thanks

[sbaffini]

Maybe you can look at how CFL3D and TLNS3D do it from the relative nasa github repositories. Not sure about the specific method they use, but it should be something close to that

[aerosayan]

Originally Posted by sbaffini

Maybe you can look at how CFL3D and TLNS3D do it from the relative nasa github repositories. Not sure about the specific method they use, but it should be something close to that

So, I did some research.
Looks like NASA's CFL3D simply adds up the fluxes in the fine grid faces, and makes up the fluxes in the coarse grid faces.


Then they calculate the residual using a) contribution of the fluxes, b) subiteration terms and 2nd order time terms, c) correction from finer level.
I understand what a) means, but not b) and c). Do you?

[sbaffini]

Originally Posted by aerosayan

So, I did some research.
Looks like NASA's CFL3D simply adds up the fluxes in the fine grid faces, and makes up the fluxes in the coarse grid faces.


Then they calculate the residual using a) contribution of the fluxes, b) subiteration terms and 2nd order time terms, c) correction from finer level.
I understand what a) means, but not b) and c). Do you?

Unfortunately, Geometric Multigrid is one of those topic that, in the time, I have always deliberately avoided learning (actually, this applies to most non textbook techniques that only work for structured grids), so I have no idea at all of what all of that means