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October 28, 2001, 14:09 
Periodic Boundary Condition problem, help

#1 
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Hi,
While model flow around a missle projectile with 4 wraparound 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? thanx. 

October 29, 2001, 03:10 
Re: Periodic Boundary Condition problem, help

#2 
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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.


October 29, 2001, 04:51 
Re: Periodic Boundary Condition problem, help

#3 
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thank u i really hadn't used hardlink, then i'll try, though dunno how to hardlink.
 ( ¡ª0¡ª  ) 

October 29, 2001, 11:06 
Re: Periodic Boundary Condition problem, help

#4 
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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.


October 30, 2001, 05:14 
Re: Periodic Boundary Condition problem, help

#5 
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thank u, OK now.
I set rotational periodic BC and Delta.P=0 in Fluent? Right? 

October 30, 2001, 11:20 
Re: Periodic Boundary Condition problem, help

#6 
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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. 

October 31, 2001, 05:08 
Re: Periodic Boundary Condition problem, help

#7 
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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.


October 31, 2001, 08:22 
Re: Periodic Boundary Condition problem, help

#8 
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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 Xdirection wind exist and the body keep stationary. So I can set in fluid BC pannel as: RotationAxis Direction: (1,0,0) MotionType:Stationary now if i want to simulate a rotating missle(Alpha=0, Phi=2rad/s), then i shall set here: RotationAxis Direction: (1,0,0) MotionType: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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