That is a pretty straightforward geometry. I should be able to be meshed with multizone method. Then on the faces of the connecting tube you would place a smaller element size and a smaller growth rate. Be sure to include an inflation layer near the walls to capture the boundary layer gradients. Or you could subdivide it into several bodies and use a multi-body part to force a 1:1 mesh between the bodies. In the middle body, you then specify a smaller body size. Again make sure that you have the inflation mesh on all the walls.