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June 19, 2010, 10:28 
twoLiquidMixingFoam

#1 
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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 = 5.30999e08, Final residual = 5.30999e08, 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 = 1.4931e08, No Iterations 6 DILUPBiCG: Solving for Uy, Initial residual = 0.0184276, Final residual = 1.39218e08, No Iterations 5 GAMG: Solving for p_rgh, Initial residual = 3.33005e07, Final residual = 3.33005e07, No Iterations 0 time step continuity errors : sum local = 6.94663e09, global = 1.76227e11, cumulative = 2.20847e08 DILUPBiCG: Solving for epsilon, Initial residual = 9.27893e08, Final residual = 9.27893e08, No Iterations 0 DILUPBiCG: Solving for k, Initial residual = 3.85187e07, Final residual = 1.09717e08, No Iterations 1 ExecutionTime = 22.01 s ClockTime = 22 s Can anyone give me any advice? Thanks. 

August 9, 2010, 05:20 

#2 
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Balkrishna Patankar
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Do try changing the relaxation values ....


August 9, 2010, 05:31 

#3 
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Maolong LIU
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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! 

August 9, 2010, 05:45 

#4 
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Balkrishna Patankar
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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 .: http://www.cfdonline.com/Forums/ope...tml#post270776 

August 9, 2010, 05:52 

#5  
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Maolong LIU
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If you don't mind, please send me your code, so I can help to check.
Quote:


August 9, 2010, 05:56 

#6 
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Balkrishna Patankar
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whats ur email ???


August 9, 2010, 05:58 

#7 
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Maolong LIU
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August 11, 2010, 01:23 

#8 
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Balkrishna Patankar
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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 ???? 

August 11, 2010, 04:05 

#9 
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Balkrishna Patankar
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got it ... the formulation is correct ....


October 27, 2010, 21:26 

#10 
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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. 

October 28, 2010, 02:39 

#11 
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Balkrishna Patankar
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that is not possible .... ur solution will diverge ....


October 28, 2010, 11:00 

#12 
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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?


November 12, 2012, 18:25 

#13 
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Kia
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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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