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Why conservation of mass is violated in Comsol - Laminar flow?

Posted Feb 7, 2011, 7:09 p.m. EST Version 4.1 2 Replies

Lichun Wang
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The model is simple, I use rectangle as my geometry(0.1505m*0.006m) ,and chose laminar flow as my module, then assign inlet boundary condition, which is pressure boundary,10[Pa], outlet condition is 0[Pa], other two boundaries are no slip boundaries. Initial value(velocity and pressure) are specified with 0. After running model, I found outlet flux(1.4441e-6m^2/s) is not equals to inlet flux(1.4491e-6 m^2/s). How does this happen even though I refine the mesh of model? Is this due to resolution of Comsol? Any help will be appreciated. Thanks a lot.

By the way, if I use a more complex geometry, then the outlet flux will more than up to 17% of inlet flux in spite of very finer mesh.
2 Replies Last Post Mar 9, 2013, 2:30 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 8, 2011, 4:13 a.m. EST
Hi

what would you expect, I see less than 1:200 difference in the values you refer to first, for me FEM is 5-10% in most cases, so I would say it's great.

Ok then you talk about 17% difference, that is in the upper limit, I agree, but are you sure you have correctly tweaked the solver so all parameters are solved with sufficient precision ? Its not only the mesh size
--
Good luck
Ivar
Hi what would you expect, I see less than 1:200 difference in the values you refer to first, for me FEM is 5-10% in most cases, so I would say it's great. Ok then you talk about 17% difference, that is in the upper limit, I agree, but are you sure you have correctly tweaked the solver so all parameters are solved with sufficient precision ? Its not only the mesh size -- Good luck Ivar
Yangguang Ou
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Posted: 1 decade ago Mar 9, 2013, 2:30 p.m. EST
Hi Ivar:

What did you mean by "tweak[ing] the solver so all parameters are solved with sufficient precision?"

Thank you.
Hi Ivar: What did you mean by "tweak[ing] the solver so all parameters are solved with sufficient precision?" Thank you.

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