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-   -   simpleFoam ddt Euler ? (http://www.cfd-online.com/Forums/openfoam-solving/77054-simplefoam-ddt-euler.html)

Mo-ITB June 11, 2010 05:53

simpleFoam ddt Euler ?
 
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...

bye,
mo

herbert June 11, 2010 06:46

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.

Regards,
Stefan

alberto June 12, 2010 13:36

Quote:

Originally Posted by Mo-ITB (Post 262600)
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.

Best,


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