Is the flow 2D or 3D if I used periodic interface?

androm · February 13, 2020, 19:03

Hello,

If I used periodic interface in CFX, is the flow 2D or 3D? I know that if I used small thickness and symmetric boundary for the front and back face of the domain, the flow considered 2D. Please, can anyone help me to understand this point?

Thanks In advance,
A.M.

ghorrocks · February 13, 2020, 19:36

Are you are asking what is the difference between a 2D model with symmetry planes on top and bottom Z faces (assuming the flow is in the XY plane), and replacing those symmetry planes with translational periodic boundaries?

If that is your question: The symmetry plane approach is closest to a true 2D simulation as no flow in the third dimension is possible. The periodic boundary approach allows flow in the third dimension, but that flow is the same at all Z values. The periodic approach is useful in axisymmetric flows with swirl as the third dimension can capture the swirl effect.

androm · February 13, 2020, 19:48

Yes, this is my question. If I want to make a heave mode for airfoil, which is 2D shape. What should I considered, periodic boundary or symmetry? Thanks.

ghorrocks · February 14, 2020, 07:01

Have a think about what my previous post said. You should be able to work it out from that. You need to understand these options for you to be able apply them.

February 13, 2020, 19:03	Is the flow 2D or 3D if I used periodic interface?	#1
androm New Member Andro Join Date: Sep 2019 Posts: 17 Rep Power: 7	Hello, If I used periodic interface in CFX, is the flow 2D or 3D? I know that if I used small thickness and symmetric boundary for the front and back face of the domain, the flow considered 2D. Please, can anyone help me to understand this point? Thanks In advance, A.M.

February 13, 2020, 19:36		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Are you are asking what is the difference between a 2D model with symmetry planes on top and bottom Z faces (assuming the flow is in the XY plane), and replacing those symmetry planes with translational periodic boundaries? If that is your question: The symmetry plane approach is closest to a true 2D simulation as no flow in the third dimension is possible. The periodic boundary approach allows flow in the third dimension, but that flow is the same at all Z values. The periodic approach is useful in axisymmetric flows with swirl as the third dimension can capture the swirl effect. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

February 14, 2020, 07:01		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Have a think about what my previous post said. You should be able to work it out from that. You need to understand these options for you to be able apply them. Opaque likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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February 13, 2020, 19:48		#3
androm New Member Andro Join Date: Sep 2019 Posts: 17 Rep Power: 7	Yes, this is my question. If I want to make a heave mode for airfoil, which is 2D shape. What should I considered, periodic boundary or symmetry? Thanks.