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tom December 15, 1999 02:46

Periodic BC in Gambit/FLUENT
Hy, 1.) In fluent there is the possibility in the text-interface to make specified boundary-faces periodic. Is it necessary to do this or is it sufficient if you make them periodic in the "normal" boundary-condition-panel ? 2.) is it ok in gambit if I link only the faces (not also the edges) of periodic faces in order to get perodic boundaries ? tom

Jonas Larsson December 15, 1999 03:46

Re: Periodic BC in Gambit/FLUENT
You have to make them periodic in the text-interface. There is a big "gotcha" there though - before you do this you have to change the rotational axis to the right axis for the fluid domain, otherwise fluent will not be able to match the two meshes. This used to me done automatically, but in the recent versions this feature has dissapeared. You do this from the "boundary conditions" window. If you still have problems to match the two meshes you can try playing a bit with the tolarance - available from the same text-menu. Fluent can be a bit sensitive to small missalignments and sometimes you have to play around a bit to get all nodes matched. If you use linked faces in Gambit it shouldn't be a problem though.

About Gambit, it is enough to link the faces. When you do this Gambit automatically also links the edges around the face.

Jonas Larsson December 15, 1999 03:54

Re: Periodic BC in Gambit/FLUENT
A small correction - the "change of axis" of course only applies to rotationally periodic faces.

Amadou Sowe December 15, 1999 12:20

Re: Periodic BC in Gambit/FLUENT
I wish Fluent would try to make the implementation of the periodic boundary condition (PBC) less ritualistic. Here is an excerpt of a workaround that was given to me by my support engineer. This was very helpful to me, I hope you find it useful too.

1) In gambit specify the zones as walls rather than use the periodic boundary condition options. For example, I would call one of the zones wall-p and the other wall-p2

2) In fluent5, specify the origin and direction of the axis for all fluid zones.

3) Using the text interface, make the periodic boundries. The make-periodic command is in the grid/modify-zones menu (see example below).

4) Repeat for all periodic zones

5) Grid check will report the rotation/translation data for each pair of periodic zones (see below) so you can check that it is setup correctly.

tom December 16, 1999 03:19

Re: Periodic BC in Gambit/FLUENT
Text-interface and bc-pannel are not the same ?

Jonas Larsson December 16, 1999 03:40

Re: Periodic BC in Gambit/FLUENT
Nope, the text interface is only available by writing commands in the main fluent window. The boundary condition panel is directly available as a menu that you can open by "clicking on it" with the mouse. The text interface has many hiiden functions in it, functions that Fluent thinks should be used with care and only by the experienced user. I don't know why the "make periodic" function is still there though.

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