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arhgang October 28, 2001 14:09

Periodic Boundary Condition problem, help

While model flow around a missle projectile with 4 wrap-around fins(Alpha=0, Farfield flow is parallel to missle axis), i use 1/4 circumferential domain in the Gambit model.

I tried to specify periodic BC to the two side faces of the quarter domain, but errors occured when export mesh.

errors: periodic boundary condition on face face.8 is incorrect and will not be written into neutral file.

BTW, cannot use Symmetry BC here, since it's wraparound fins rather than 4 cross fins.

the relation of two side faces, i think, are one's in = another's out, so i tried periodic BC.

How to correct this error? or any else way?


kim October 29, 2001 03:10

Re: Periodic Boundary Condition problem, help
Did you hardlinked the meshes on the periodic faces ? Did you assign the periodic BC for both faces in pair ? These are the necessary conditions for correct export of mesh.

arhgang October 29, 2001 04:51

Re: Periodic Boundary Condition problem, help
thank u i really hadn't used hardlink, then i'll try, though dunno how to hardlink.

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Lanre October 29, 2001 11:06

Re: Periodic Boundary Condition problem, help
Go to the Mesh Faces tool pad and click on the hard link (the first button on the left, lower row). For rotationally periodic faces like the ones you describe, make sure you check the "reverse orientation" box.

arhgang October 30, 2001 05:14

Re: Periodic Boundary Condition problem, help
thank u, OK now.

I set rotational periodic BC and Delta.P=0 in Fluent? Right?

arhgang October 30, 2001 11:20

Re: Periodic Boundary Condition problem, help
because the whole calculation domain was decomposed into several volumes, so each side was built up by 3 conplane conjoint faces.

I set 3 pairs of faces as hardlinked. so 3 periodic BC created.

periodic.4 periodic.5 periodic.6

then two conjoint edge was defined as Axis BC, now problem came, --axis bc cannot be exported with mesh! Gambit reported that no entity was related with the edges.

when build case in fluent, no axis bc was seen in BC selections.(rotaional periodic BC need axis, right?)

why? i have no idea.

kim October 31, 2001 05:08

Re: Periodic Boundary Condition problem, help
You do not have to set any axis BC. You just mark rotational in periodic BC panel. Rotation speed and axis of rotation is set in fluid panel and wall panel.

arhgang October 31, 2001 08:22

Re: Periodic Boundary Condition problem, help
thank u, Kim and Lanre

You remind me sth. deep in my mind. At first I was about to simulate a stationary missle, that is, only X-direction wind exist and the body keep stationary. So I can set in fluid BC pannel as:

Rotation-Axis Direction: (1,0,0)

Motion-Type:Stationary now if i want to simulate a rotating missle(Alpha=0, Phi=2rad/s), then i shall set here:

Rotation-Axis Direction: (1,0,0)

Motion-Type:Moving Mesh

Rotational Velocity Speed: 2 rad/s

Translational Velocity: (0,0,0)

and the mesh is the same as mentioned above.

am i right?

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