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Momentum source in periodic BC

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Old   January 15, 2008, 11:16
Default Momentum source in periodic BC
  #1
Mann
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Hi

With normal boundary conditions (Inlet & Outlet) my solution crashes. Therefore, I have set up periodic boundary condition for my LES simulation right at the out set of simulation. Is it going to affect my results if i set up periodic BC before i achieve convergence.

How critical is it to specify pressure change or mass flow rate in periodic BC. I have specified neither! I would like to have constant pressure gradient in my simulation. Does anyone know how to specify that! Thanks in advance for your help.
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Old   January 15, 2008, 17:35
Default Re: Momentum source in periodic BC
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Glenn Horrocks
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Hi,

Boundary conditions are tricky in LES as you have to create a turbulent field (that is including the large turbulent eddies) at inflow boundaries. The standard CFX inlet does not let you do that.

If periodicity is applicable to your simulation you can get it , but then you have to be careful to use the pressure difference or massflow rate carefully to get the correct flow.

I have not done this but I suspect driving the flow with a mass flow rate will be more stable for LES applications. Just my guess.

Glenn Horrocks
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Old   January 16, 2008, 16:07
Default Re: Periodic BC for the energy equation
  #3
Ahmad Al-Zoubi
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Hi all and Hi Glenn,

What about solving the energy for a periodic system such as in finned heat exchanger. In CFX11 there is no direct way to specify the temperature at the periodic boundaries.

Regards

Ahmad
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Old   January 16, 2008, 18:21
Default Re: Periodic BC for the energy equation
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Glenn Horrocks
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Hi,

I think you are correct - I don't think you can do a temperature rise with periodic boundaries. I would ask support about this, there may be a way of doing it which is not documented.

Glenn Horrocks
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Old   January 18, 2008, 08:02
Default Re: Periodic BC for the energy equation
  #5
Ahmad Al-Zoubi
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Hi Glenn,

I have asked the cfx-support here and they have no clear idea how to do it. Maybe you can manage it.

Regards. Ahmad
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Old   January 20, 2008, 18:06
Default Re: Periodic BC for the energy equation
  #6
Glenn Horrocks
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Hi,

No, I can't. If your local support office can't do it then ask them to send it to "head office" in the US.

Glenn Horrocks
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