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Old   June 11, 2010, 05:53
Default simpleFoam ddt Euler ?
Moritz Wied
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Hi Foamers,

i made some funny experiences with simpleFoam. As is switched from piso to simple i forgot to change the ddtScheme from Euler to steadyState in the fvSchemes.

now if i changed the timestep to a very low value (1e-11), i was able to run simpleFoam with a quick convergence and a result that looks very good.

my setup:
- air flow arround ahmed body
- LamBremhorstKE lowRe
- velocity 40 m/s
- polymesh made with ccm+ with 10 surface layers
- k eps bounded

if i use pisoFoam or simpleFoam with ddtScheme steadyState, i have to start with a low velocity and carefully rise it step by step not to diverge with k and epsilon.

with ddtScheme Euler and the timestep 1e-11 (nothing else changed), it converges with bc 40 m/s and initial field 0 m/s without rising step by step.

Does anybody know, if simpleFoam can "officialy" be used for transient calculations or how the ddt term is taken into account?

Maybe this might also help somebody to get a initial field...

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Old   June 11, 2010, 06:46
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Stefan Herbert
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Hi Moritz,

all the equations in simpleFoam do not include any ddt-terms. Therefore time scheme is not used at all. But inside the turbulence model it is used. I don't think that your results could be this good, because solving k- and epsilon-equations with such a small time-step (1e-11!) would be like underrelaxation of near zero! Then you won't have any trouble concerning convergence, of course, but on the other hand your results won't change, do they?

In general simpleFoam cannot be used for transient calculations.

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Old   June 12, 2010, 13:36
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Alberto Passalacqua
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Originally Posted by Mo-ITB View Post
Does anybody know, if simpleFoam can "officialy" be used for transient calculations or how the ddt term is taken into account?
No, simpleFoam is a steady-only solver (no ddt in UEqn). If you want a transient or pseudo-transient solver, take a look at pimpleFoam.

Alberto Passalacqua

GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image.
OpenQBMM - An open-source implementation of quadrature-based moment methods
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