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Question on OpenFOAM and implicit time discretization

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Old   March 10, 2016, 18:32
Default Question on OpenFOAM and implicit time discretization
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Hello folks,

OpenFOAM has quite a few implicit time schemes which are used pretty heavily. But what I don't understand is that often in practice and a lot of advice on this forum says you should still try to get a CFL of 1, even though the implicit scheme shouldn't require that.

I have found, though, that in many instances without this, the code blows up. For my higher-speed cases, this can happen with dt=1e-4s. With much smaller timesteps, 1e-5s or 1e-6, the code doesn't blow up. Does this represent some kind of instability in the scheme, or am I missing something?

Thanks.
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Old   March 11, 2016, 04:05
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The time marching is stable, the system coupling is not.
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