Aspect Ratio at high turbulent and swirled flows

zago

hi everybody!

while i was simulating a gascyclone i have mentioned a special behaviour of the solution. when i´m refine the grid in radial direction the tangential velocity increases as aspected. unfortunately the axial velocity decreases until i don´t refine the grid in axial direction. i think that this behaviour is caused by the deterioration of the aspect ratio.

my questions:

1) has anybody experience with that kind of problem?

2) i have heard that the permissed aspect ratio that is stated in the fluent user manual is to high for high turbulent and swirled flows (e.g. gascyclone flows). does anybody know values for the aspect ratio that should be achieved for that problem???

thanx christoph