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Periodic B.C or Inlet/Outlet B.C

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Old   February 24, 2010, 08:41
Question Periodic B.C or Inlet/Outlet B.C
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alireza
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Hi guys

I want to know that, how can I use icoFoam for the laminar microchannel and which of the boundary condition need to use, periodic or inlet/outlet.

Thanks,
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Old   February 25, 2010, 02:19
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Tammo Wenterodt
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If you want to simulate a fully developed channel flow in constant cross sections or in a periodically repeating geometry, the cyclic boundary condition for the U-field is what you need. The easiest way to prescribe a pressure drop between inlet and outlet is to use the fan-boundary condition. I.e. in constant/polyMesh/blockMeshDict use e.g.
Code:
cyclic inout
  (
    (4 7 3 0)
    (6 5 1 2)
  )
Then in 0/U
Code:
  inout
  {
    type cyclic;
    value uniform (0 0 0);
  }
In 0/p write
Code:
inout
  {
    type fan;
    patchType cyclic;
    f List<scalar> 1(-0.005); // p_OF = p_real / rho
    value uniform 0;
  }
and mind that the OpenFOAM pressure is divided by the density in incompressible flow. The pressure drop (here 0.005*rho) that is needed for a certain mean velocity can be calculated by the Poisseuille number (if available) or must be guessed and then corrected. (Yes, I know there is channelFoam, but I cannot recommand that for various reasons.)
Here the "value"-entries are only used for the first iteration (and to prevent paraFoam from crashing) and are then overwritten.
Good luck!
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Old   February 25, 2010, 04:58
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Hi,

an other way is to use mapped boundary condtions.

Fully developed flow boundary condition

Regards Thomas
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Old   February 27, 2010, 04:36
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alireza
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Quote:
Originally Posted by wenterodt View Post
If you want to simulate a fully developed channel flow in constant cross sections or in a periodically repeating geometry, the cyclic boundary condition for the U-field is what you need. The easiest way to prescribe a pressure drop between inlet and outlet is to use the fan-boundary condition. I.e. in constant/polyMesh/blockMeshDict use e.g.
Code:
cyclic inout
  (
    (4 7 3 0)
    (6 5 1 2)
  )
Then in 0/U
Code:
  inout
  {
    type cyclic;
    value uniform (0 0 0);
  }
In 0/p write
Code:
inout
  {
    type fan;
    patchType cyclic;
    f List<scalar> 1(-0.005); // p_OF = p_real / rho
    value uniform 0;
  }
and mind that the OpenFOAM pressure is divided by the density in incompressible flow. The pressure drop (here 0.005*rho) that is needed for a certain mean velocity can be calculated by the Poisseuille number (if available) or must be guessed and then corrected. (Yes, I know there is channelFoam, but I cannot recommand that for various reasons.)
Here the "value"-entries are only used for the first iteration (and to prevent paraFoam from crashing) and are then overwritten.
Good luck!
Dear Tammo

thanks for your help. but, I have some other questions. could you tell me, what is the Fan-boundary condition and is it possible to use this B.C in icoFoam. also, I want to know for laminar channel flow, can I use icoFoam?
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