Double Tube Flow
 

hi;

i want to solve a natural convection in a double tube. water flows thorough the innert tube, and there is air in the annuli (and there is a natural convetion there). i can not set up the problem because there is an interface between two tubes. i send a figure in attachment about geometry and boundary conditions.

if i select interface boundary condition for "interface" fluent says "WARNING: mesh check failed.
"To get more detailed information about the mesh check failure
increase the mesh check verbosity via the TUI command
/mesh/check-verbosity. "


if i select wall boundary condition for "interface" then fluent creats a interface-shadow. i select coubled under "thermal conditions" then define other boundary conditons.

when i came the initialize section there is already "-1.#IND" in the velocity inlet and all zones. i delete that and put actual values. but fluent could not solve the problem, say "divergence detected in AMG solver: x-momentum"

what can i do, how can i solve this problem i defined.

thanks already


sorry for poor english