Hi Butterfly users,
I have been trying to understand the refinement levels of butterfly but I am not able to understand how butterfly arrive with any cell sizes. the cell size on the butterfly WTGrading component is limited to only 2 intergers, and I don’t understand, what is it’s effect.
I suspected that the XYZGrad component is how we can set up the level of refinements. However, I am not sure what are each input/output means. Could anybody direct me to a documentation on this matter?
maybe someone can explain to me what does this mean?
(1.0 20.0 1.0)
(3.0 60.0 1.0)
(6.0 20.0 1.0)
(0.5 70.0 1.0)
(0.5 30.0 1.0)
Thank you so much!
It gradually changes the size of the cells throughout the tunnel. It’s a step you can use before you do the snappyHexMesh.
The below will grade in the Y direction
hex (0 1 2 3 4 5 6 7) (100 300 100) // number of cells in each direction X,Y,Z
1 // x-direction expansion ratio 1 = constant = not changing
( // start Y direction
(0.2 0.3 4) // 20% y-dir, 30% cells, expansion = 4
(0.6 0.4 1) // 60% y-dir, 40% cells, expansion = 1
(0.2 0.3 0.25) // 20% y-dir, 30% cells, expansion = 0.25 (1/4)
) // end Y direction
3 // z-direction expansion ratio
Read more here https://cfd.direct/openfoam/user-guide/v6-blockmesh/
You can generate these numbers using this guy (unless you scripted them in GH)
Example image below showing a graded mesh:
Y (up here) direction is building up in size, let’s say 10-15% per cell as you move up.
X is building down to around the 40% mark (40% of the distance measured from left)
then its constant from 40 to 60% mark,
and builds up from 60 to 100%…
Have in mind that you should not increase the step per cell by more than around 10-15%. Also, make sure that all the cells close to your buildings are close to cube shape, otherwise you’ll get problems with snappyHexMesh.
@TheodorosGalanos also has a tutorial on this on Performance Network
Best, Mathias Sønderskov