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Old   June 19, 2010, 10:28
Default twoLiquidMixingFoam
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Maolong LIU
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Hi, because the twoLiquidMixingFoam in OpenFoam is a transent solver. I was trying to change it to a steady state solver according to simpleFoam and twoLiquidMixingFoam.
Now the new solver can run successfully and it seems that the calculation result is correct. I compared u with experiment result and previous transient result.

But the problem is that there is a converge problem. After run a long time, pressure, k, epsilon etc. are all converged, but onlu u does not converge.

Time = 30575

DILUPBiCG: Solving for alpha1, Initial residual = 5.30999e-08, Final residual = 5.30999e-08, No Iterations 0
Phase 1 volume fraction = 0.500002 Min(alpha1) = 0 Max(alpha1) = 1
DILUPBiCG: Solving for Ux, Initial residual = 0.135853, Final residual = 1.4931e-08, No Iterations 6
DILUPBiCG: Solving for Uy, Initial residual = 0.0184276, Final residual = 1.39218e-08, No Iterations 5
GAMG: Solving for p_rgh, Initial residual = 3.33005e-07, Final residual = 3.33005e-07, No Iterations 0
time step continuity errors : sum local = 6.94663e-09, global = -1.76227e-11, cumulative = 2.20847e-08
DILUPBiCG: Solving for epsilon, Initial residual = 9.27893e-08, Final residual = 9.27893e-08, No Iterations 0
DILUPBiCG: Solving for k, Initial residual = 3.85187e-07, Final residual = 1.09717e-08, No Iterations 1
ExecutionTime = 22.01 s ClockTime = 22 s


Can anyone give me any advice? Thanks.
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Old   August 9, 2010, 05:20
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Balkrishna Patankar
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Do try changing the relaxation values ....
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Old   August 9, 2010, 05:31
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Thank you for your reply. I modified the U equation
UEqn== -fvc::grad(p)

to

UEqn== fvc::reconstruct
(
......
)
according to the twoLiquidMixingFoam, and now this problem has been solved.

Now I am trying to speed up the convergence because my mesh number is really huge.
Now the procedure of this solver is
first solver U eqn
and then p eqn
and then alpha1 eqn.
Also I change the relax method of alpha eqn just like p eqn (restore alpha1 and relax alpha1 instead alpha1 eqn).

How do you think of it?
Thank you!
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Do try changing the relaxation values ....
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Old   August 9, 2010, 05:45
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thats a nice modification .... relaxing alpha1 after every loop does converge faster ....
I am working on something similar and facing a ver different problem ... pls do help ...
link to thread discussion here .: Extending OpenFOAM ::: error
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Old   August 9, 2010, 05:52
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If you don't mind, please send me your code, so I can help to check.

Quote:
Originally Posted by balkrishna View Post
thats a nice modification .... relaxing alpha1 after every loop does converge faster ....
I am working on something similar and facing a ver different problem ... pls do help ...
link to thread discussion here .: Extending OpenFOAM ::: error
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Old   August 9, 2010, 05:56
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whats ur email ???
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Old   August 9, 2010, 05:58
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maolongliu@gmail.com

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whats ur email ???
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Old   August 11, 2010, 01:23
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In the twoLiquidMixingFoam what exactly is alpha1 ?? according to the o/p statement ,
it represents volume fraction , but how is the conservation equation formed on the basis of volume fraction ?
i mean conservation equation is :
d/dt(rho_fluid*mass_K) + divergence(rho_fluid*U*mass_K)= convection + source terms ....
where rho_fluid is density of the mixture ....
mass_K is the mass fraction of the Kth component ....
....
How is this written in terms of the volume fraction alpha ????
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Old   August 11, 2010, 04:05
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got it ... the formulation is correct ....
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Old   October 27, 2010, 21:26
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Has anyone seen negative values for alpha1 in twoLiquidMixingFoam? If so, any idea what changes I can make to correct the problem? I'm runnig a simulation of a pipe with RE around 2000 that has water and a higher viscosity fluid (~25cP). Any help is appreciated.

Thanks in advance!

Phase 1 volume fraction = 0.000377962 Min(alpha1) = -2.37485 Max(alpha1) = 1

Last edited by phinallydone; October 27, 2010 at 21:48.
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Old   October 28, 2010, 02:39
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that is not possible .... ur solution will diverge ....
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Old   October 28, 2010, 11:00
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That's just it... it's not diverging. I've tried refining the mesh, relaxing alpha1, and adjustnig tols. Any ideas?
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Old   November 12, 2012, 17:25
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Hey Maolong,

Can you tell me how you changed the solver to steady state. I am working on a similar problem and my delta T is really small and will like to make it steady state to avoid the Courant number restriction.
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