problem in using multizone
 

Thanks for advice ghorrocks.
I have already used tetra mesh, but RMS values are not smaller than 1e-4.
Therefore I want to use hexa mesh. I can see with large hexa mesh my RMS are smaller than 1e-4 and my problem is converged.

If I do not use multizone and use hexa simply with small mesh size,there are meshes with too large size in the center part of my circular conduit.

I can use tetra mesh with body sizing .4m accompanied with multizone, but I can not use smaller size mesh. Error is indicated in following picture:
What should I do?
Please give me some advice!
Best regards.

If I do not use multizone and use small mesh size , result is indicated in the picture:

I can use smaller mesh (.2m) with multizone(Free Surface Type: not allowed) but results are not good.(Water pressure and air velocity are too large )I want to use Inflation but I cannot use inflation. I faced with error.

Which surfaces should be select im my work for inflation?
In multizone:
Which option should be use? Hexa or Hexa/prism.

and which option should be use for Free Mesh Type? not allowed or tetra or Hexa dominant or hexa core.

Which surface should be use for source surface in my work?

pictures are as shown:


Can every one help me?