How OpenFOAM calculate flux and the other face's field in split-Hex cells?

Hgholami · January 14, 2021, 11:16

Dear foamer,
I have question about flux calculation in split-Hex cell of snappyHexMesh. In regular mesh with blockMesh, each cell face connect to only a face of neighbor cell. So flux will calculate with owner and neighbor cell.
In generated mesh with snappyHexMesh, we have a face of a neighbor cell that connected to two face of two cells.

How OpenFOAM calculate flux and the other face's field in split-Hex cells?
Thanks,

simrego · January 15, 2021, 06:18

Hi!

Interpolate the cell values to the face centres (ie velocity field), then multiply by the face area normal and you get the flux on the face.
There is no way that one face belongs to more than 2 cells. When you have a "split-hex" mesh, the faces will be splitted too so the face count on the "big cell" will increase.
Let's imagine you have a neighbour. But your neighbour will be splitted. So earlier you had one face to your neighbour, but now you have two neighbours, and you have 2 different faces to them.

In your example the 2 resulted faces after the split are aligned so it seems like there is one face. But in reality there are 2 faces or even more on the left side (there you have even more for some cells which is not a good idea, but possible..

January 14, 2021, 11:16	How OpenFOAM calculate flux and the other face's field in split-Hex cells?	#1
Hgholami Senior Member Hojatollah Gholami Join Date: Jan 2019 Posts: 171 Rep Power: 7	Dear foamer, I have question about flux calculation in split-Hex cell of snappyHexMesh. In regular mesh with blockMesh, each cell face connect to only a face of neighbor cell. So flux will calculate with owner and neighbor cell. In generated mesh with snappyHexMesh, we have a face of a neighbor cell that connected to two face of two cells. How OpenFOAM calculate flux and the other face's field in split-Hex cells? Thanks,

January 15, 2021, 06:18		#2
simrego Senior Member anonymous Join Date: Jan 2016 Posts: 416 Rep Power: 14	Hi! Interpolate the cell values to the face centres (ie velocity field), then multiply by the face area normal and you get the flux on the face. There is no way that one face belongs to more than 2 cells. When you have a "split-hex" mesh, the faces will be splitted too so the face count on the "big cell" will increase. Let's imagine you have a neighbour. But your neighbour will be splitted. So earlier you had one face to your neighbour, but now you have two neighbours, and you have 2 different faces to them. In your example the 2 resulted faces after the split are aligned so it seems like there is one face. But in reality there are 2 faces or even more on the left side (there you have even more for some cells which is not a good idea, but possible.. Hgholami likes this.