Meshing a pipe
 

Hi,
I am trying to create a pipe model, (a 40mm dia pipe whose end is connected to 20mm dia pipe) with only upper half of the entire cylinder (pipes) SO AS TO TAKE ADVANTAGE OF SYMMETRY. I have a query regarding the mesh to be made at the interface of larger and smaller pipe i.e the face containing end of larger pipe and beginning of smaller pipe.
Am I supposed to create a separate face at that area for meshing (we have 2 semicircles corresponding to cross sections of larger and smaller pipe) so as to have consistency in my entire model, rather than having a concentrated mesh at that area due to intersection of 2 volumes or is it a good method to have more detailed mesh at that area for studying velocity profile?

Thank you

Well I am trying this model in Gambit

Thank you