How to refine O-grid hexa mesh?

Pete

Hi,

I'm doing some mesh dependency test for my elbow diffuser. I used the hexa mesh with O topology. Just wonder if anyone has experience in refining this type of mesh effectively?

I tried to double the grid point on all grid lines but the number of elements increases tremendously. Any idea how to arrange it in such a way that the asymtotic solution can be observed/estimated properly and yet the number of nodes is not increased tremendously?

Thanks for your advice.

Cheers, Pete