generate a graded pipe mesh.
 

Hi,

I'm trying to generate a 'doughnut' pipe mesh with different levels of refinement at different parts of the pipe using blockMesh.
I want the mesh to be fine in the middle of the pipe and coarse at the inlet and outlet sides.

I create the pipe mesh using a script that allows me to specify the outer and inner radius of the pipe (attached).

I've used the refineHexMesh utility on cells within a bounding box near the centre of the pipe. I also tried snappyHexMesh to refine the region inside a searchable box.
However, both of these seemed to refine in only one direction and the edges from the refined region didn't connect well with the non-refined region. I hope you can see this in the attached screenshot.

Does anyone have any suggestions?
Is it possible to modify my script to get refinement in a specific part of the pipe?

Thanks,
Jim