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-   -   Boundary condition for periodic flow solution in Gambit (http://www.cfd-online.com/Forums/main/98814-boundary-condition-periodic-flow-solution-gambit.html)

ghmahtabi March 20, 2012 03:38

Boundary condition for periodic flow solution in Gambit
 
Using periodic condition for the entrance and exit of a channel, I solve a problem in Gambit, trying to reach a fully developed velocity distribution pattern. But the problem I face is that Gambit won't allow the action for some settings concerning boundary condition maybe mistaken.Any Ideas for boundary condition settings?
Yours, Etc.

sbaffini March 20, 2012 14:36

Dear ghorban,

there is a basic distinction between setting boundary conditions in a grid generator (say gambit) and setting them in a solver (say Fluent).

What you do in a grid generator is simply putting a label on a face/volume or a group of faces/volumes which then is hopefully recognized by the selected solver. The real b.c. setting and or modification actually happens in the solver, which nonetheless can be helped by the settings in the grid generator.

The case of periodicity in the Gambit/Fluent couple is non standard with respect to the other boundary conditions and requires a little more explanation.

First, in Gambit you may have to use the periodicity function (i don't remember now the actual name) for the selected couple of periodic faces. That is, if you mesh them with an unstructured grid it is unlikely that they will end up with the same traslated/rotated face mesh unless you use this option. However, this is a grid generation option and has nothing to do with the boundary conditions.

Second, to use periodicity in Fluent, you can simply leave the two faces as walls in gambit and then, after reading the grid, digit within the Fluent TUI:

/mesh/modify-zones/make-periodic

which prompts you some questions to define the periodicity. After that, the periodic conditions have to be defined, that is a driving pressure gradient or mass flow rate has to be defined. And you are done.

ghmahtabi March 20, 2012 17:22

Dear Paolo
thank you for valuable guidance,they were very profitable for me.
with regard.


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