Smaller pipe connected to a larger pipe - Hexa blocking
 

Hi all,

Thank you for reading my first post on this awesome forum.

I have been struggling with the problem that can seen in the attached picture. There is a cut plane going through two pipes.

If I have a pipe with a small diameter connected to a pipe having a larger diameter, how can I avoid that the boundary layer inflation of the smaller pipe goes through the larger pipe? I have tried to avoid this by making those skewed cells seen in the picture.

Another issue is that after the small pipe I would not need such a fine mesh in the center of the larger pipe. The biggest gradients of my flow develop more close to the walls. Is there any way not to have this fine mesh in the center?

The only idea I currently have is to mesh the large pipe separately and use a nonconformal interface between the small and the large pipe meshes. Because my flow has high turbulence and combustion close to that interface, I suppose nonconformal mesh is not a good idea?

I hope someone could help me with this issue, propably I just don't get something as a beginner. Maybe some other approach than HEXA blocking would be better for this problem? Please feel free to ask more details.

BR, Niko

Well, I played with the edge parameters, did some more splitting for the blocks and associated the vertices in a different way. This resulted in a mesh which seems to work quite well.

I had some convergence problems because the continuity residual got stuck (stopped decreasing). Interestingly, when I changed the gradient discretization to green-gauss node based the convergence is a lot better. I hope the mesh works also with the second order discretization because now I have only tried the first order.