Simplefoam, steady or unsteady
 

Hi FOAMERS
SIMPLEFOAM is steady, (due to the manual), but when I am running pitzDaily with it, why do I get a solution at times t = 0 to 1000 s?

Hi,

The original simpleFoam solver is for the steady calculations. In steady calculations,
deltaT has no effect on the results and is usually set to 1 so that the time means the
number of iterations.

Hope that helps,
fumiya

Hi,
If simpleFoam is for steady calculations, then why is it possible to change the ddtScheme into "Euler" rather than "steadyState" in system/fvSchemes ?

is it ok to apply this change ?

When I tested this on a cylinder at RE = 100 it gave me the same results for Cd and strouhal.
By the way, the results are far from the experiments. With the solver piso and ico, the same mesh and boundary conditions, it is better.

It makes me think that the simple Solver solver should never be used as a transient solver.
Am i right ?

simpleFoam is an steady-state solver and those changes has no effect on result

Thank you, it makes sense now.

It is quite confusing to let the user write Euler in the ddtSchemes. It would be better to fix this scheme as steadyState.

Hi Mahdi,

i don't know exactly how openFOAM deals with steady state but, one approach is to consider it as transient called (pseudo transient) it add transient term (d/dt) and start run from sensible values like starting from rest (it is easier to get these values for transient than steady state). it deals with transient term in different way from piso algorithm to accelerate solution. finally, you should ignore all values in developing time and only take into consider values after developing time when values become fixed.

good luck :)

Hi ,Fumiya! I want to use LES turbulence model to simulate steady state of wind turbine with smagorinsky model. Could you tell me if I could choose the SimpleFoam solver?I see there are some articles with the method of LES in steady state but not in OF,So I am wondering how to achieve it. I know that LES method are usually used in trasient condition, I want to make sure does the LES inconsistent with simplefoam solver because when I run the MRFSimpleFoam ,it shows the error cannot find the file RASProperties. Could you help me ?

It does not make any sense to do steady state LES simulations. I would be interested in any articles showing this. Of coarse, you can run a transient solver, on a stable, physically steady case, but this does not make it a steady state solver.

《Steady-State Large-Eddy Simulations to Study the Stratocumulus to Shallow Cumulus Cloud Transition 》 http://journals.ametsoc.org/doi/abs/...urnalCode=atsc

Hi jiaojiao,
did u find an answer on doing LES for a steady state flow?
Ayla

simpleFoam steady or unsteady
 

Hi Foamers,

I know this can be a silly question. I know that simple foam is a steady state solver and the delta T means the iteration number.

When i run my simulation i get this

Time = 1

smoothSolver: Solving for Ux, Initial residual = 1, Final residual = 7.827025e-13, No Iterations 20
smoothSolver: Solving for Uy, Initial residual = 1, Final residual = 5.0458368e-13, No Iterations 22
smoothSolver: Solving for Uz, Initial residual = 1, Final residual = 3.9496433e-13, No Iterations 25
GAMG: Solving for p, Initial residual = 1, Final residual = 3.6324613e-11, No Iterations 1000
time step continuity errors : sum local = 6.3981153e-14, global = 3.4832047e-17, cumulative = 3.4832047e-17
smoothSolver: Solving for omega, Initial residual = 0.17479046, Final residual = 5.3209563e-13, No Iterations 20
smoothSolver: Solving for k, Initial residual = 1, Final residual = 7.9795701e-13, No Iterations 22
ExecutionTime = 104.1 s ClockTime = 109 s

So what does No iterations mean here?
I think in trasient solvers there are inner iteration loops .
This is confusing me could some one help me. I tried to go through the simpleFoam.c but i couldnt crack it.

Regards,
Naresh

Those iteration numbers are for solution convergence in each time iteration

Thank you so much Nima for the quick reply.

Just to clarify , please correct me if i m wrong.

1. These iterations depends on the tolerance value i specify in the FVsolution.
And the tolerance is also global so it stops the simulation when the required convergence is achevied.

solvers
{
p
{
solver GAMG;
tolerance 1e-06;
relTol 1e-06;
smoother GaussSeidel;
nPreSweeps 0;
nPostSweeps 2;
cacheAgglomeration on;
agglomerator faceAreaPair;
nCellsInCoarsestLevel 10;
mergeLevels 1;
}

"(U|k|epsilon|omega|R|nuTilda)"
{
solver smoothSolver;
smoother symGaussSeidel;
tolerance 1e-06;
relTol 1e-06;
}
}

now i have a doubt if "reltol" plays a role in the inner iterations. Thank you for your time.

with regards,
Naresh