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Mass flow rate boundary condition with negative values

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Old   November 25, 2014, 21:34
Question Mass flow rate boundary condition with negative values
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Ashkan Javadzadegan
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Dear all,
I am modelling flow in a pipe. My inlet boundary condition is mass flow rate which is initially positive and toward the mid flow cycle becomes negative and eventually becomes positive toward the end of flow cycle.
If I set the mass flow rate as the inlet boundary condition, will the flow enter the flow domain when the mass flow is negative? How is it possible to set a negative mass flow rate as inlet boundary condition in CFX-Pre?

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AshtonJ
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Old   November 26, 2014, 00:24
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Glenn Horrocks
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Have you tried it? Give it a go and see what happens.

I suspect an outflow mass flow boundary will fail as you need to define additional flow parameters (eg temperature, turbulence etc) when flow enters a domain and you cannot set this on an outlet.

But it might work for an inlet.
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Old   November 26, 2014, 00:30
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Ashkan Javadzadegan
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Actually the model is running now.
If CFX gives error, will switching the boundary condition to "opening" help?
If not, is there any other method to consider the negative mass flow rate in CFX. The negative mass flow is very common case in arteries ...
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Old   November 26, 2014, 05:21
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If you know the flow direction is going to reverse then yes, I would recommend using an opening.
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