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eb.nabizadeh July 26, 2012 17:04

solver setting
can any one help me please?
i have a 3D model(a house)that i want to check temp & flow in model is transient & the volume of it is 400m3,walls are at initial temp 20 c and when wind blowing into it exchange it's heat with walls.but i have some problem in convergence.i want some one to say exact setting about my model.what under-relaxation factor is good for it,which viscose model is better.finally what must i do to converge my problem.thanks

eb.nabizadeh July 26, 2012 17:15

i don't have much time please help me early

Bionico July 27, 2012 02:12

Hello :)
If I were you I would try first with a k-epsilon model (Realizable o RNG).
Maybe it's better to reduce the URF (M=0.2 E=0.9 should be enough).
First order upwind for discretization and PRESTO! for pressure scheme.

Sixkillers July 27, 2012 03:55

Also It depends which model you use for air density. Are using ideal gas model or Boussinesq approximation? Generally speaking ideal gas model is harder to converge.

eb.nabizadeh July 27, 2012 09:50

i use Boussinesq model for density.i want to know what criterion(surface integrals) can i consider except residual?

eb.nabizadeh July 28, 2012 04:16

dear Bionico
when in do what you said i facing this error:floating point exception!
and when i change my turbulence model it didn't converge.
can you help me more?

Bionico July 30, 2012 02:42

ok, it's a convergence problem...
since this is a transient simulation, try reducing the Courant number under 1 :)

eb.nabizadeh July 30, 2012 17:45

you mean i use density based or pressure based?

Bionico July 31, 2012 02:01

No, but maybe (I don't remember very well) the Courant number can be controlled only in COUPLED problem (not if you have a SIMPLE one).
Therefore try reducing time step and increasing number of iteration/time step :)

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