Multiphase simulation wall setting

Hi everyone. I have a problem about define wall in multiphase flow.

In example fallingDroplet3D
the syntax listed below was used to set the shape of the wall.
Box3D bottom (0, nx-1, 0, ny-1, 0, 0);
setToConstant(fields.flag, bottom, (int) twoPhaseFlag::wall);

Can I Know if I want to create a Sphere shape wall, How can I do it?

I tried to use the way that used in cylinder2d. but it didn’t work.

Thank you very much!