[walakaka]

Hi everyone,

I am trying to simulate a two-phase stratified flow in a pipe. However, my simulations are taking extremely long. It states that it takes 1001 iterations to obtain pressure , does anyone know what could be the cause of this issue?

PIMPLE: iteration 1
smoothSolver: Solving for alpha.water, Initial residual = 0.000529543, Final residual = 2.66809e-11, No Iterations 2
Phase-1 volume fraction = 0.517887 Min(alpha.water) = 0 Max(alpha.water) = 1.06837
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Phase-1 volume fraction = 0.517887 Min(alpha.water) = -8.72144e-07 Max(alpha.water) = 1.06794
DICPCG: Solving for p_rgh, Initial residual = 1, Final residual = 0.880426, No Iterations 1001
time step continuity errors : sum local = 0.00204219, global = -2.39327e-05, cumulative = -4.39327e-05
DICPCG: Solving for p_rgh, Initial residual = 0.270516, Final residual = 0.753417, No Iterations 1001
time step continuity errors : sum local = 0.00579181, global = -2.39253e-05, cumulative = -6.7858e-05
DICPCG: Solving for p_rgh, Initial residual = 0.510678, Final residual = 0.1488, No Iterations 1001
time step continuity errors : sum local = 0.00170815, global = -1.19552e-05, cumulative = -7.98132e-05
ExecutionTime = 12.26 s ClockTime = 12 s

Regards
Shafik

[piu58]

You get such effects if something wrong with your boundary or initial conditions. Or you set up your case in a non physical way.

[walakaka]

Originally Posted by piu58

You get such effects if something wrong with your boundary or initial conditions. Or you set up your case in a non physical way.

Hi, thank you for your reply!

Could you kindly elaborate what you mean by wrong boundary/initial conditions or non physical?
Because I am getting accurate results when modelling single phase flow (Unless it is possible to obtain good results with my error). Which is why I am confused, what do you mean by wrong boundary/initial conditions or non physical way?

Kind regards
Shafik

[piu58]

Good morning,

if yopu take additional effects in to account, the behaviour of the solver may change. Somtimes, it ist more or less a different solver.

I see two ways that anybody may help you. Either you reduce the effect you see to the simples thinkable case and report is as an error. Or you describe what is your real problem and which connection to the physical worls it has. May be there are other ways to solve it.

[walakaka]

Originally Posted by piu58

Good morning,

if yopu take additional effects in to account, the behaviour of the solver may change. Somtimes, it ist more or less a different solver.

I see two ways that anybody may help you. Either you reduce the effect you see to the simples thinkable case and report is as an error. Or you describe what is your real problem and which connection to the physical worls it has. May be there are other ways to solve it.

Good morning!

Thank you for your kind reply. I am currently using the interFoam solver which uses the Pimple algorithm. I notice that when I change the deltaT, the number of iterations required for pressure correction to converge reduces!

Is there an explanation for this?

Regards
Shafik