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Input and output flow mismatch

Posted 16.08.2015, 03:35 GMT-4 Fluid & Heat, Computational Fluid Dynamics (CFD) Version 4.4 2 Replies

Houari Cobas
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Hello, how are you doing?
I´m simulating a simple flow system channel with an input and three outputs. When i compute the input flow trough a boundary integration at each one of the input and outputs i realize that the total input flow does not match the total output flow. In my case, the total output flow is higher than the input flow.
Can someone tell me why this should be happening? How can i correct this problem?

Thank you very much
2 Replies Last Post 17.08.2015, 11:30 GMT-4
Lasse Murtomäki
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Posted: 9 years ago 17.08.2015, 01:53 GMT-4
I had the similar problem when I had narrow capillaries where the flow took place. Using swept mesh in the radial direction with symmetric geometrical distribution removed the problem. In my case, the outflow was thrice the inflow.
I had the similar problem when I had narrow capillaries where the flow took place. Using swept mesh in the radial direction with symmetric geometrical distribution removed the problem. In my case, the outflow was thrice the inflow.
Houari Cobas
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Posted: 9 years ago 17.08.2015, 11:30 GMT-4
Hi Lase, thank you for your reply.
I think i had worked out the problem. In the output boundary condition i selected the "normal flow" check box. With this option selected the difference between input and output flow was reduced drastically. I had an relative error (between input and ouput flow) below 4%. So then i start reducing the mesh resolution in the input and ouput boundaries. With this the relative error fall below 1.65%. So i assume the model is now respecting the flow continuity. The remaining difference would be reduced increasing the mesh resolution at those boundaries.

Thank you very much
Hi Lase, thank you for your reply. I think i had worked out the problem. In the output boundary condition i selected the "normal flow" check box. With this option selected the difference between input and output flow was reduced drastically. I had an relative error (between input and ouput flow) below 4%. So then i start reducing the mesh resolution in the input and ouput boundaries. With this the relative error fall below 1.65%. So i assume the model is now respecting the flow continuity. The remaining difference would be reduced increasing the mesh resolution at those boundaries. Thank you very much

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