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A simple question about inlet boundary of flow simulation

Posted 2 lug 2012, 11:48 GMT-4 Fluid & Heat, Computational Fluid Dynamics (CFD), Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers Version 4.2a 1 Reply

Hongzi Mao
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I want to simulate a simple situation where inlet flow is constant flow rate, say 10 cm^3/s. But when I type this number in the inlet boundary, there always an error says "failed to find solution". I have changed the initial value or used step function to make the change smooth, but it didn't seem to help.

I guess it is somehow because the inlet flow condition may be violate with "no-slip" wall.. Do someone know how I can deal with this situation? Using s*(1-s) that kind of parabola function ( I am not very familiar with it) or anything else?

Thanks for helping the fledgling.



Best regards,

Mao
1 Reply Last Post 2 lug 2012, 16:48 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2 lug 2012, 16:48 GMT-4
Hi

in CFD you can ask for an extra laminar inflow region (and I believe now also outflow region, havent tried this yet), but be aware that if you define apressure at inlet, its at the additional length inlet it stands for, not at your true on-scree model inlet.

Then if you have one sinle inlet boundary, you can write a V=V0*4*s*(1-s) to get a parabolioc max flow (or 6 instead of 4 for a mean flow rate) with v=0 at the boundaries(s=0,1). But this works only for 2D, in 3D you must write ut the equations a bit more

--
Good luck
Ivar
Hi in CFD you can ask for an extra laminar inflow region (and I believe now also outflow region, havent tried this yet), but be aware that if you define apressure at inlet, its at the additional length inlet it stands for, not at your true on-scree model inlet. Then if you have one sinle inlet boundary, you can write a V=V0*4*s*(1-s) to get a parabolioc max flow (or 6 instead of 4 for a mean flow rate) with v=0 at the boundaries(s=0,1). But this works only for 2D, in 3D you must write ut the equations a bit more -- Good luck Ivar

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