Fundamental Question about Rotating wall!
 

Dear all;

suppose we want to model a 3-bladed fan in a duct. I konw that we have to use either:
-SRF (MRF when duct is not surface of revolution)
-Sliding mesh
-Moving mesh

My simple(!) question is:

why we cant just use moving wall boundary condition for the fan blades? i.e. no need to define rotating frame or ....

I think if the the rotating wall was axissymmetric like a cylinder or a disk, then it would be reasonable. Am I right?

Thanks in advance for your reply!

You are right. Simply applying a rotating wall boundary condition only works if the wall is a surface of revolution (of course with the same axis of rotation).

This is not applicable if the wall is not a surface of revolution because in this case, the wall would acually move through the fluid domain.
This is not possible.

An immersed boundary would be another option for a rotating body.