I am researching about buried (submerged) Vane to control scour at Vertical Wall Abutments with flow-3d software so this issue is so important simulated in correct way.
use the NURBS Modelling from Rhinocerous3D to create the surfaces, and after that recreate the Model using the KUBRIX software from Itasca Inc. U will get the Jacobean correctors of the mesh.
No! It depends! The mesh must be small for those region with high flow property gradient for a flow simulation to be able to converge. The the cell in those region are set too lagre, you might not be able to converge. How to setup? You can cut your domain into several block and use different seting for each blocks. Just be careful the shape of cells and change rate of cell size should not too large.