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-   -   Opening BC for multiphase problem (http://www.cfd-online.com/Forums/cfx/21749-opening-bc-multiphase-problem.html)

John October 25, 2005 11:06

Opening BC for multiphase problem
 
Hi, all

Does someone have expeience of defining an opening BC for a gas-liquid phase problem? It seems that I need to input both gas liquid velocities. However I do not know that.

Please give some comments, Thanks!

Best regards!

John

Rui October 25, 2005 11:22

Re: Opening BC for multiphase problem
 
Hi,

Whether it's a multi-phase or a single-phase problem, on an Opening BC you may input the pressure instead of velocity.

Take a look at the Documentation, Solver Modelling - Boundary Condition Modelling - Opening, and Solver Theory - Basic Solver Capability Theory - Boundary Conditions - Opening

Regards,

Rui

John October 25, 2005 11:37

Re: Opening BC for multiphase problem
 
Hi, Rui

Thanks for your reply.

Yes, I can choose to input pressure, however in that case I need to input volume fractions of gas and liquid as well. I also need to know the values of the additional variables at opening location, which I do not know.

Thanks!

John


Rui October 25, 2005 12:46

Re: Opening BC for multiphase problem
 
Hi,

The volume fractions and the additional variables values at the Opening BC will only be used for flow into the domain.

If in your Opening BC there is actually flow into the domain, you have to know the volume fractions and the additional variables values that are flowing into your domain.

But there's another option which isn't mentioned in the Documentation, and which you may only be set editing the .ccl file: BOUNDARY : out
Boundary Type = OPENING
Location = out
BOUNDARY CONDITIONS :
MASS AND MOMENTUM :
Option = <font color="red">Extrapolation</font>
END
END
END




However, this was told to me by the CFX support: "Note that this type of treatment of the b.c. should not be used for a steady state case, as it is not constrained enough"I never used this type of definition, so I don't know if it works well or not.

Regards,

Rui


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