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Old   April 3, 2009, 05:28
Default interTrackFoam timestep
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Virginie Ehrlacher
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Hello,

I am trying to simulate the flow of a viscous liquid (viscosity 100) over a slope, and I am having problems with the tolerated timestep.

Indeed, the more viscous my liquid is, the smaller the timestep should be for my simulation to run. I managed to make it bigger by choosing a CrankNicholson ddt scheme and by implementing a PISO loop rather than a SIMPLE one but it is still very low.

I am quite astonished because in Fluent, I can get far bigger timestep for the same kind of simulation (but without the moving meshes).

Could someone explain to me why it is so? Or could give me any advice on how I could get a bigger timestep for my simulation. Thank you.

Virginie
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Old   April 3, 2009, 06:30
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Sebastian Gatzka
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Hi!

What is your setting for maxCo in controlDict?

I experienced far better solution times with interDyMFoam when using the GAMG solver. I don't know if this is applicable to interTrackFoam...
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Old   April 3, 2009, 10:42
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Can you quantify the timeStep? What order of magnitude is it?

Simulations involving interface tracking use explicit surface updates, even if the bulk fluid is solved implicitly. Convection and diffusion is solved implicitly in most solvers that I've seen in FOAM.
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Old   April 6, 2009, 04:20
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Hello,

I did not set a maxCo because it is not originally taken into account in interTrackFoam (and at the beginning I did not want to change anything in the solver). So the maximum time step I could set was 2.10-5 (for a viscosity of 100) and my Co values are about 0.001. By reading the user guide, I thought that I could hace Co values which could reach about 0.2...

And if I set a greater timestep than 2.10-5, I get a floating point exception very quickly.

I tried to change the viscosity of my fluid, and typically, with a viscosity of 10, I could reach a timestep of 2.10-4... I am astonished, I would have thought that I would have got a lower time step.

Thank you for your help anyway.

Virginie
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Old   April 6, 2009, 05:02
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Sorry I had forgotten some information:

the order of magnitude is: 0.05 m.s-1
the typical size of the edges of my mesh is of order 0.005 m
and my total simulation domain is over a 1m length

hope it will help

Virginie
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