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January 29, 2013, 14:53 |
Novice question
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#1 |
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 65
Rep Power: 14 |
Hi All,
I am trying to get an LES case to converge, and I am having some difficulty. The case runs fine in FLUENT, but the pressure residual blows up in OpenFOAM. My mesh is great, timestep is really small (Co <0.05), so I believe my BCs are the problem. In FLUENT the outlet is set to outlet-vent. Can someone tell me how to set that in OpenFOAM. I jus want to double check what I've done. Currently for U I have: Outlet type inletOutlet; inletValue uniform (0 0 0); value uniform (0 0 0); For P I have: OUTLET { type fixedValue; value uniform 0; } Cheers |
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January 30, 2013, 05:55 |
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#2 |
Senior Member
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Hello Anonymous,
It seems indeed your boundary conditions may lead to these divergence problems, similar problems where found here: http://www.cfd-online.com/Forums/ope...buildings.html Maybe they have found a solution, regards, Tom |
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January 30, 2013, 10:52 |
Thanks
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#3 |
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 65
Rep Power: 14 |
Thanks Tom,
I had a look at the forum, and it helped. I had a question...what outlet Boundary condition in OpenFOAM would match an outlet-vent condition in FLUENT. In FLUENT, the outlet-vent condition allows backflow, but both the outflow and backflow have a pressure drop across the vent, proportional to the velocity (either in or out). Like a loss coefficient for a valve. Cheers |
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January 30, 2013, 11:30 |
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#4 | |
Member
Eric Robertson
Join Date: Jul 2012
Posts: 95
Rep Power: 14 |
Quote:
http://www.foamcfd.org/Nabla/guides/...ml#x32-1640293 Maybe pressureInletVelocity or something similar for U? |
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January 30, 2013, 11:32 |
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#5 |
Senior Member
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I don't think there is a standard boundary condition available that is similar. I did experiment a bit with LES, but I am not an expert. Also I have no experience with Fluent, so I guess I am not the best person to give you more advice.
I only have one more suggestion: The way you prescribe the Fluent boundary condition sounds like a sponge layer with backflow calculated based on pressure difference, maybe it helps to use pressureInletOutletVelocity instead of inletOutlet with inletVelocity uniform(0 0 0)? Regards, Tom |
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January 30, 2013, 12:43 |
Reply
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#6 |
Member
Anonymous
Join Date: Jan 2012
Location: Canada
Posts: 65
Rep Power: 14 |
Thanks Tom,
I will give that a try, they both sound similar. Boundary conditions for LES are very difficult, especially if they arent cyclical. Thanks again, Cheers |
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