[srv537]

i am a new user of OpenFoam and CFD.
i have used ansys fluent and there is no input parameter for time in steady case simulation,but
for every simulation of OpenFoam we have to specify delta T (time) and end time, so how can i simulate steady case?
how can i decide that my simulation is now in steady state.
please explain. can you suggest me some tutorial or guide for learning openfoam.

[jmdf]

The delta T you specify on the steady state cases are just for counting the iterations, so the best practice is to use 1.
A steady state case can be solve using steady state solvers, like simpleFoam.

Check the pitzDaily tutorial, the fvSolution contains the entry for the simple algorithm which defines the residual values for each variable. As soon as the residuals are below that value, the simulation stops and the case is considered converged (keep in mind that these values are inserted by the user).

$FOAM_TUTORIALS/incompressible/simpleFoam/pitzDaily

Hope it helps!

[srv537]

Originally Posted by jmdf

The delta T you specify on the steady state cases are just for counting the iterations, so the best practice is to use 1.
A steady state case can be solve using steady state solvers, like simpleFoam.

Check the pitzDaily tutorial, the fvSolution contains the entry for the simple algorithm which defines the residual values for each variable. As soon as the residuals are below that value, the simulation stops and the case is considered converged (keep in mind that these values are inserted by the user).

$FOAM_TUTORIALS/incompressible/simpleFoam/pitzDaily

Hope it helps!

so we can use any unsteady solver for steady simulation and we just need to modify delta time as 1?
am i right? so icoFoam will work for steady, laminar, Newtonian fluid if i change delta time to 1?

and in openfoam manual simpleFoam is for Steady-state solver for incompressible, turbulent flow. i read in a post and tried for laminar case by modifying turbulenceProperties file in constant folder model as 'laminar' and turbulent off but i got a message
FOAM FATAL ERROR:
Unknown RASModel type laminar

Valid RASModel types:

17
(
LRR
LamBremhorstKE
LaunderSharmaKE
LienCubicKE
LienLeschziner
RNGkEpsilon
SSG
ShihQuadraticKE
SpalartAllmaras
kEpsilon
kOmega
kOmegaSST
kOmegaSSTSAS
kkLOmega
qZeta
realizableKE
v2f
)
pls help me

thank!

[srv537]

i tried icoFoam for steady case with delta time = 1 and i got an error

Courant Number mean: 4185.94 max: 25065.3
#0 Foam::error:rintStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 ? in "/lib/x86_64-linux-gnu/libc.so.6"
#3 Foam::symGaussSeidelSmoother::smooth(Foam::word const&, Foam::Field<double>&, Foam::lduMatrix const&, Foam::Field<double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&, unsigned char, int) at ??:?
#4 Foam::symGaussSeidelSmoother::smooth(Foam::Field<d ouble>&, Foam::Field<double> const&, unsigned char, int) const at ??:?
#5 Foam::smoothSolver::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:?
#6 ? at ??:?
#7 ? at ??:?
#8 ? at ??:?
#9 ? at ??:?
#10 __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#11 ? at ??:?
Floating point exception (core dumped)

[pupo]

Originally Posted by srv537

so we can use any unsteady solver for steady simulation and we just need to modify delta time as 1?
am i right? so icoFoam will work for steady, laminar, Newtonian fluid if i change delta time to 1?

Different solvers have different algorithms designed for steady or unsteady problems. It is possible to use unsteady solver for steady simulations but the way to do this is going to the fvSchemes file and setting

ddtSchemes           { default steadyState; }

You will also need to modify the remaining schemes to better suit the type of problem being solved. (I can't help you with this sorry)


Setting delta to 1 is just a convention. When using a steady state solver, the solver will still do "time" iterations. these however are physically meaningless so they are used to count iterations. Setting deltat to 0.001 or to 1 has no impact on the results.

[srv537]

Originally Posted by pupo

Different solvers have different algorithms designed for steady or unsteady problems. It is possible to use unsteady solver for steady simulations but the way to do this is going to the fvSchemes file and setting

ddtSchemes           { default steadyState; }

You will also need to modify the remaining schemes to better suit the type of problem being solved. (I can't help you with this sorry)


Setting delta to 1 is just a convention. When using a steady state solver, the solver will still do "time" iterations. these however are physically meaningless so they are used to count iterations. Setting deltat to 0.001 or to 1 has no impact on the results.

then which solver i should use for steady laminar Newtonian fluid ?
thanks again

[pupo]

Originally Posted by srv537

then which solver i should use for steady laminar Newtonian fluid ?
thanks again

It seems that IcoFOAM is indeed the best choice, but you will have to read some more on the correct numerical schemes to be used. I'm afraid i don't know enough about this to provide any meaningful help.

Alternatevely, SimpleFOAM can be used. Depending on your problem you may find a tutorial that is highly identical to yours, just be sure to turn off turbulence by setting

simulationType  laminar;

in constant/turbolenceProperties