[sinhavivekananda318]

Hello all,
I am simulating a pulse column case in interFoam. While solving I am getting negative alpha value in the calculations ..but that is too small ..it is in the order of e-12. Is it an error?
This is the following message I am getting
PIMPLE: iteration 1
smoothSolver: Solving for alpha.water, Initial residual = 0.00162047, Final residual = 1.25822e-09, No Iterations 3
Phase-1 volume fraction = 0.647771 Min(alpha.water) = -1.27725e-08 Max(alpha.water) = 1
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Phase-1 volume fraction = 0.647771 Min(alpha.water) = -6.51804e-06 Max(alpha.water) = 1.00001
DICPCG: Solving for p_rgh, Initial residual = 0.0278935, Final residual = 0.00110561, No Iterations 2
time step continuity errors : sum local = 5.69383e-05, global = -6.09452e-09, cumulative = -6.0192e-07
DICPCG: Solving for p_rgh, Initial residual = 0.00119511, Final residual = 5.10015e-05, No Iterations 9
time step continuity errors : sum local = 2.62867e-06, global = -9.61851e-10, cumulative = -6.02881e-07
DICPCG: Solving for p_rgh, Initial residual = 0.000109429, Final residual = 9.72348e-08, No Iterations 420
time step continuity errors : sum local = 5.01138e-09, global = -2.42982e-11, cumulative = -6.02906e-07
ExecutionTime = 3239.45 s ClockTime = 3445 s

Any kind of help will be appreciated....

[clemerlin]

Hello snihavivekananda318,

By experience, it is only some numerical fluctuations during your simulation. As long as your minimum value stays around e-6 it is not an error to me. If you want to reduce it you should reduce the tolerance in the fvSolution file.

Cheers

[sinhavivekananda318]

actually I was thinking that being a physical quantity the value alpha should be between 0 to 1..negative value would be unphysical..but I am getting negative value of alpha..though it is very very small but still it is negative..that is why this doubt is here...if you could clarify pls....

[Taataa]

Generally, you should use a bounded scheme for alpha (usually vanLeer for (phi,alpha) and interfaceCompression for (phirb,alpha). Also if you're NOT using MULES you can use vanLeer01.

Anyhow, in your case it doesn't seems to an issue.

[mszeto715]

Hi Taher,

Can you elaborate on why you can't use vanLeer01 with MULES?

Thanks.
Mimi

[Taataa]

because MULES iteself takes care of under- and over-shoots and you don't want to over smooth the solution.