pimpleDyMFoam -- lowered viscosity -- time step continuity errors getting large

pbachant · October 31, 2013, 09:17

I'm working on some cases with pimpleDyMFoam, which I have gotten to mesh and solve fairly well, but then when I go to drop nu from 1e-6 to 6.7e-7, I am getting time step continuity errors that go up into the 6000 range after a few seconds. This then sets my deltaT so low that the solution effectively halts. Any ideas why this would happen?

Artur · November 4, 2013, 04:37

My guess would be something happening with either:

Code:

div((nuEff*dev(T(grad(U)))))

or with the turbulent quantities. So either fvSolution or fvSchemes file. Perhaps changing to a lower order scheme, different equation solver, adding underrelaxation or pushing down your tolerances would prevent it from blowing up. It would all depend on how the process actually takes place - showing your log file would help a bit in determining what is actually going on.

Are you using the same mesh for both viscosities? What kind of moving mesh are you using?

All the best,

A

October 31, 2013, 09:17	pimpleDyMFoam -- lowered viscosity -- time step continuity errors getting large	#1
pbachant Senior Member Pete Bachant Join Date: Jun 2012 Location: Boston, MA Posts: 173 Rep Power: 13	I'm working on some cases with pimpleDyMFoam, which I have gotten to mesh and solve fairly well, but then when I go to drop nu from 1e-6 to 6.7e-7, I am getting time step continuity errors that go up into the 6000 range after a few seconds. This then sets my deltaT so low that the solution effectively halts. Any ideas why this would happen?

November 4, 2013, 04:37		#2
Artur Senior Member Artur Join Date: May 2013 Location: Southampton, UK Posts: 372 Rep Power: 19	My guess would be something happening with either: Code: div((nuEff*dev(T(grad(U))))) or with the turbulent quantities. So either fvSolution or fvSchemes file. Perhaps changing to a lower order scheme, different equation solver, adding underrelaxation or pushing down your tolerances would prevent it from blowing up. It would all depend on how the process actually takes place - showing your log file would help a bit in determining what is actually going on. Are you using the same mesh for both viscosities? What kind of moving mesh are you using? All the best, A

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