Hello,everybody:

Have you solved such problem as specifying the flow direction in setting up the periodic boundary conditions? Now I meet the this problem . My flow is moving axisymmetrically around a disk, and the periodic bounary is the cross section through the axis. So the flow is flowing normally to the periodic bounary . It is neither in the x direction, nor y or z, you can say it's circumferential and radial simultaneously, or flowing spirally. Then how can I specify the flow direction, can you help me?

Any answer will be appreciated. I'm looking forward to your reply!

Best wishes!

You can impose a pressure gradient in the direction of the periodic flow..then the flow will choose the direction from the highest to the smallest pressure....

Thank you for your reply!

still I'm wondering, in my model, it does not allow a pressure drop across the periodic planes, so I specify the pressure gradient as 0, how could I casually specify the pressure gradient when it is zero or certain value that I don't know?

second, even if I've imposed a pressure gradient , the option of flowing direction still has to be specified, as you can find, this option appears in the right corner of the dialoguobox of periodic boundary condition.

waiting for your further explanation!

regards,joanna.