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Boundary conditions( flow in pipe)
Posted 2011年1月1日 GMT-5 05:15 Fluid & Heat, Studies & Solvers Version 3.5a 5 Replies
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i am trying to make model of non-isothermal flow in pipe.
Now i have 2 problems:
1) i want to model flow in pipe working under pressure, so i need "inlet" and "outlet" in boundary conditions for entrance and exit from the pipe. what must they are?
Am i right?
and i am from russia, we have another terminology =(, so where can i read what means for example "Pressure, no viscous stress" ?
2) when i solve my model (2D , Axial symmetry) i always get some errors like
relative preconditioned residual is less than the required tolerance
Thank you very much))
Happy new year =)
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happy new year
I assume you are rather right for point 1)
for 2) it could come from v4.0a ? the solver settings are not optimal in the first version of v4, it's better in 4.1, from my experience it's either from a scaling issue or a mesh density issue
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Good luck
Ivar
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i change version and its work! very good, thank you for good advise)
Excuse me, can you help me one more question?
what boundary conditions must i set if i get simple pipe with pressure at the entrance 1 MPa and at the exit the pressure will be 1MPa - pressure losses ? But pressure losses depends of temperature, velocity and so on.....
may be there is some better idea?
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I'm not the best on CFD, and spcially I'm still fighting with the issue of "absolute" and "gauge" pressure in COMSOL, so each time I make me up a simple case, check analytically and then validate.
If you have a pressure driven fow, you need the absolute pressure at the "inlet", then if the exit is free 1[atm] is for me a normal absolute pressure, just check carefully how your COMSOL physics is setting up the equation (check the doc in 4.1 it's much more complete than it was in v4.0) and try out a few simple cases
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Good luck
Ivar
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yes , there is something strange with pressure.
Your solutions help me, thank a lot =)
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It's not strange, it's reproducible and a matter of normalisation, but not the one that seems the most logic for me, I need to find some time (what I never have, I'm always too busy) to study more CFD ;)
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Good luck
Ivar