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Stability startup problems with rhoSimpleFoam |
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July 10, 2006, 07:58 |
I've select rhoSimpleFoam as a
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Senior Member
Mark Olesen
Join Date: Mar 2009
Location: https://olesenm.github.io/
Posts: 1,695
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I've select rhoSimpleFoam as a starting point for using openFOAM for standard industrial applications - steady-state, k/eps, moderate compressibility - thus my apologies for posting with presumably banal questions.
Backtracking from my original geometry, I am now using blockMesh to create a very simple test case. I assume that encountered stability problems arise from incorrect configuration, but I am uncertain as to what I should be changing. The test geometry is a simple square duct (50mmx50mm) with a u-bend. The inlet is L/D = 1, the bend is R/D = 1, and the outlet is L/D = 10. I've used surfaceNormalFixedValue for the inlet velocity and fixedValue (1.1e5) for the outlet pressure. With U=15m/s, I obtain a physically reasonable result (relaxation parameters 0.3/0.7). At a slightly higher inlet velocity (U=20m/s), the solution seems to diverge rapidly regardless of the relaxation parameters (lowest tried was 0.05/0.3). I really cannot figure out if the difficulty arises from the physics (outlet too close) or from incorrect specification of the BCs and/or schemes. Ideally the inlet would be specified as an integral mass-flux, which would also alleviate the divergence problem, but I cannot imagine that this is the sole factor here. If anyone has a few minutes to look at the problem and see what is going awry, I would be greatly appreciate it. I could also offer the problem for a potential rhoSimpleFoam tutorial. Thanks, /mark |
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