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October 19, 2014, 14:38 
negative min.(alpha1) value interFoam

#1 
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Arjun
Join Date: Jan 2014
Location: Chennai
Posts: 21
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Hi...
I am new to openFoam, for the past week I am stuck with my problem. I am trying to simulate water falling on a circular tube surface. interFoam was selected as the base solver with dambreak as the base case. slight modification were made with files of dambreak. internalField was set as uniform 0. alpha.water for inlet as type fixedValue and value uniform 1. Wall B.C's as zeroGradient. p_rgh B.C's internalField uniform 0 walls as type fixedFluxPressure; value uniform 0; inlet as type fixedValue; value uniform 0; U B.C's internalField uniform 0 wall as type fixedValue; value uniform (0 0 0); inlet as type flowRateInletVelocity; massFlowRate constant 0.1; rhoInlet 1; setFields as defaultFieldValues ( volScalarFieldValue alpha.water 0 ); After some time steps min(alpha1) deviates to too negative value. the terminal shows Time = 0.000215 smoothSolver: Solving for alpha.water, Initial residual = 0.135945, Final residual = 4.85033e09, No Iterations 6 Phase1 volume fraction = 3.89404e14 Min(alpha1) = 0.494288 Max(alpha1) = 1 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase1 volume fraction = 3.89404e14 Min(alpha1) = 0.494288 Max(alpha1) = 1 DICPCG: Solving for p_rgh, Initial residual = 0.421282, Final residual = 0.0204154, No Iterations 6 time step continuity errors : sum local = 9.04479e07, global = 1.89978e07, cumulative = 5.23877e07 DICPCG: Solving for p_rgh, Initial residual = 0.304169, Final residual = 0.0149129, No Iterations 5 time step continuity errors : sum local = 8.80687e07, global = 1.71627e07, cumulative = 6.95504e07 DICPCG: Solving for p_rgh, Initial residual = 0.244908, Final residual = 9.59156e08, No Iterations 462 time step continuity errors : sum local = 6.22699e12, global = 1.30827e14, cumulative = 6.95504e07 ExecutionTime = 3316.69 s ClockTime = 4119 s Courant Number mean: 5.63527e05 max: 5.31579 Interface Courant Number mean: 2.13444e06 max: 2.08533 Time = 0.00022 smoothSolver: Solving for alpha.water, Initial residual = 0.173116, Final residual = 5.69664e09, No Iterations 14 Phase1 volume fraction = 5.2177e14 Min(alpha1) = 0.70481 Max(alpha1) = 1 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase1 volume fraction = 5.2177e14 Min(alpha1) = 0.70481 Max(alpha1) = 1 DICPCG: Solving for p_rgh, Initial residual = 0.381394, Final residual = 0.0167599, No Iterations 10 time step continuity errors : sum local = 1.58839e06, global = 2.25771e07, cumulative = 9.21275e07 DICPCG: Solving for p_rgh, Initial residual = 0.271973, Final residual = 0.0121764, No Iterations 5 time step continuity errors : sum local = 1.32254e06, global = 6.32625e08, cumulative = 9.84538e07 DICPCG: Solving for p_rgh, Initial residual = 0.191749, Final residual = 9.99155e08, No Iterations 469 time step continuity errors : sum local = 1.11654e11, global = 9.08119e14, cumulative = 9.84538e07 ExecutionTime = 3398.03 s ClockTime = 4207 s Courant Number mean: 8.40514e05 max: 8.08132 Interface Courant Number mean: 4.53269e06 max: 4.24642 Time = 0.000225 smoothSolver: Solving for alpha.water, Initial residual = 0.170608, Final residual = 3.34717e09, No Iterations 10 Phase1 volume fraction = 1.10859e13 Min(alpha1) = 0.56912 Max(alpha1) = 1 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase1 volume fraction = 1.10859e13 Min(alpha1) = 0.56912 Max(alpha1) = 1 DICPCG: Solving for p_rgh, Initial residual = 0.418703, Final residual = 0.0192012, No Iterations 5 time step continuity errors : sum local = 2.23831e06, global = 6.45109e08, cumulative = 1.04905e06 DICPCG: Solving for p_rgh, Initial residual = 0.264399, Final residual = 0.0117227, No Iterations 5 time step continuity errors : sum local = 1.56011e06, global = 2.27227e07, cumulative = 8.21821e07 DICPCG: Solving for p_rgh, Initial residual = 0.161567, Final residual = 9.91333e08, No Iterations 465 time step continuity errors : sum local = 1.33674e11, global = 9.29279e14, cumulative = 8.21821e07 ExecutionTime = 3476.99 s ClockTime = 4294 s Courant Number mean: 0.000106596 max: 9.31549 Interface Courant Number mean: 5.9444e06 max: 3.21124 Time = 0.00023 smoothSolver: Solving for alpha.water, Initial residual = 0.174622, Final residual = 8.06469e09, No Iterations 8 Phase1 volume fraction = 1.36574e13 Min(alpha1) = 1.08339 Max(alpha1) = 1 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase1 volume fraction = 1.36574e13 Min(alpha1) = 1.08339 Max(alpha1) = 1 DICPCG: Solving for p_rgh, Initial residual = 0.563562, Final residual = 0.0271184, No Iterations 4 time step continuity errors : sum local = 3.22933e06, global = 3.09184e07, cumulative = 1.13101e06 DICPCG: Solving for p_rgh, Initial residual = 0.325179, Final residual = 0.0159427, No Iterations 5 time step continuity errors : sum local = 2.12216e06, global = 2.7194e07, cumulative = 1.40295e06 DICPCG: Solving for p_rgh, Initial residual = 0.218524, Final residual = 9.34715e08, No Iterations 480 time step continuity errors : sum local = 1.2633e11, global = 8.28896e14, cumulative = 1.40295e06 ExecutionTime = 3557.34 s ClockTime = 4382 s Courant Number mean: 0.000124486 max: 9.14801 Interface Courant Number mean: 5.45008e06 max: 1.54779 Time = 0.000235 smoothSolver: Solving for alpha.water, Initial residual = 0.203736, Final residual = 9.52402e09, No Iterations 17 Phase1 volume fraction = 3.94801e13 Min(alpha1) = 0.606969 Max(alpha1) = 1 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase1 volume fraction = 3.94801e13 Min(alpha1) = 0.606969 Max(alpha1) = 1 DICPCG: Solving for p_rgh, Initial residual = 0.110379, Final residual = 0.00435067, No Iterations 2 time step continuity errors : sum local = 9.18565e06, global = 8.93057e08, cumulative = 1.49225e06 DICPCG: Solving for p_rgh, Initial residual = 0.0295617, Final residual = 0.00142974, No Iterations 5 time step continuity errors : sum local = 3.09834e06, global = 3.46288e07, cumulative = 1.14596e06 DICPCG: Solving for p_rgh, Initial residual = 0.0228198, Final residual = 9.75055e08, No Iterations 453 time step continuity errors : sum local = 2.164e10, global = 9.17758e13, cumulative = 1.14596e06 ExecutionTime = 3635.92 s ClockTime = 4469 s Courant Number mean: 0.000156587 max: 22.8963 Interface Courant Number mean: 7.49421e06 max: 2.03706 Time = 0.00024 smoothSolver: Solving for alpha.water, Initial residual = 0.20387, Final residual = 3.9583e09, No Iterations 13 Phase1 volume fraction = 6.13117e13 Min(alpha1) = 4.09164 Max(alpha1) = 1 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase1 volume fraction = 6.13117e13 Min(alpha1) = 4.09164 Max(alpha1) = 1 DICPCG: Solving for p_rgh, Initial residual = 0.749905, Final residual = 0.0333727, No Iterations 9 time step continuity errors : sum local = 9.46227e06, global = 3.61406e06, cumulative = 4.76002e06 DICPCG: Solving for p_rgh, Initial residual = 0.307627, Final residual = 0.01456, No Iterations 6 time step continuity errors : sum local = 6.64208e06, global = 1.50695e06, cumulative = 6.26697e06 DICPCG: Solving for p_rgh, Initial residual = 0.160218, Final residual = 9.90744e08, No Iterations 489 time step continuity errors : sum local = 4.83966e11, global = 2.85499e13, cumulative = 6.26697e06 ExecutionTime = 3718.94 s ClockTime = 4560 s Courant Number mean: 0.000414007 max: 145.401 Interface Courant Number mean: 9.92862e06 max: 5.30545 Time = 0.000245 smoothSolver: Solving for alpha.water, Initial residual = 0.426234, Final residual = 8.67918e09, No Iterations 50 Phase1 volume fraction = 6.7424e14 Min(alpha1) = 5.62255 Max(alpha1) = 1 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase1 volume fraction = 6.7424e14 Min(alpha1) = 5.54044 Max(alpha1) = 1.9061 DICPCG: Solving for p_rgh, Initial residual = 0.801868, Final residual = 0.0396942, No Iterations 4 time step continuity errors : sum local = 2.10043e05, global = 7.37201e06, cumulative = 1.3639e05 DICPCG: Solving for p_rgh, Initial residual = 0.166809, Final residual = 0.00802116, No Iterations 6 time step continuity errors : sum local = 2.94754e05, global = 1.06916e05, cumulative = 2.43305e05 exit DICPCG: Solving for p_rgh, Initial residual = 0.330884, Final residual = 9.89421e08, No Iterations 501 time step continuity errors : sum local = 3.14305e10, global = 6.02658e13, cumulative = 2.43305e05 ExecutionTime = 3811.48 s ClockTime = 4667 s Courant Number mean: 0.00181847 max: 479.069 Interface Courant Number mean: 0.000605703 max: 479.069 Time = 0.00025 smoothSolver: Solving for alpha.water, Initial residual = 0.702312, Final residual = 9.28023e09, No Iterations 66 Phase1 volume fraction = 3.41965e12 Min(alpha1) = 18.9554 Max(alpha1) = 1 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase1 volume fraction = 3.41965e12 Min(alpha1) = 15.4267 Max(alpha1) = 6.79324 DICPCG: Solving for p_rgh, Initial residual = 0.563373, Final residual = 0.0229745, No Iterations 5 time step continuity errors : sum local = 4.96062e05, global = 1.45167e05, cumulative = 3.88473e05 really confused with what to do? Thanks in advance. 

October 20, 2014, 02:54 

#2 
Senior Member
Fabian Roesler
Join Date: Mar 2009
Location: Germany
Posts: 210
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From the first glimpse I'd say you miss an outlet boundary. But I can't tell for sure until you post your p_rgh an U files. You let water flow into a domain. As for interFoam, all phases including gas/air are incompressible, some material has to leave the domain to fulfill continuity. Add an atmosphere at the top or an outlet boundary at the bottom of your domain.
Cheers Fabian 

October 20, 2014, 03:38 

#3 
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Arjun
Join Date: Jan 2014
Location: Chennai
Posts: 21
Rep Power: 4 
Dear Fabian,
Thanks for your time.... My p_rgh... internalField uniform 0; boundaryField { WALL { type fixedFluxPressure; value uniform 0; } TUBEWALL { type fixedFluxPressure; value uniform 0; } INLET { type fixedFluxPressure; value uniform 0; } OUTLET { type totalPressure; value uniform 0; p0 uniform 0; U U; phi phi; gamma 1; value uniform 1; } FRONTANDBACK { type fixedFluxPressure; value uniform 0; } } U file... internalField uniform (0 0 0); boundaryField { WALL { type fixedValue; value uniform (0 0 0); } TUBEWALL { type fixedValue; value uniform (0 0 0); } INLET { type fixedValue; value uniform (0 0.03 0); } OUTLET { type pressureInletOutletVelocity; value uniform (0 0.03 0); } FRONTANDBACK { type fixedValue; value uniform (0 0 0); } } thanks in advance 

October 20, 2014, 04:38 

#4 
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Fabian Roesler
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Location: Germany
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So now I see, that you have an atmosphere boundary condition. So my first guess was wrong. But I also see, that your Courant number is quite big for multi phase simulations with interFoam. Could you post a picture of your simulation domain and the mesh you use? You could try to increase the nonOrthCorrectors and do a checkMesh to see if your mesh is sufficient for simulation.


October 20, 2014, 04:42 

#5 
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Fabian Roesler
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An one more question! Do you use fixed time steps? This could be the reason for the high Courant number. Change adjustTimeSteps to true in controlDict.


October 20, 2014, 05:23 

#6 
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Arjun
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Dear Fabian,
checkMesh will give.... Create time Create polyMesh for time = 0 Time = 0 Mesh stats points: 161101 faces: 1658928 internal faces: 1571476 cells: 807601 faces per cell: 4 boundary patches: 7 point zones: 0 face zones: 0 cell zones: 0 Overall number of cells of each type: hexahedra: 0 prisms: 0 wedges: 0 pyramids: 0 tet wedges: 0 tetrahedra: 807601 polyhedra: 0 Checking topology... Boundary definition OK. Cell to face addressing OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces... Patch Faces Points Surface topology INLET 2995 1595 ok (nonclosed singly connected) WALL 9201 4856 ok (nonclosed singly connected) SPLITWALL 16917 8651 ok (nonclosed singly connected) FRONTANDBACK 28636 15114 ok (nonclosed singly connected) TUBEWALL 14408 7572 ok (nonclosed singly connected) SYMMETRY 9446 4942 ok (nonclosed singly connected) OUTLET 5849 3101 ok (nonclosed singly connected) Checking geometry... Overall domain bounding box (0 0 0) (20 35.4 10) Mesh (nonempty, nonwedge) directions (1 1 1) Mesh (nonempty) directions (1 1 1) Boundary openness (1.87929e15 7.48659e16 1.06194e16) OK. Max cell openness = 2.68207e16 OK. Max aspect ratio = 5.77614 OK. Minimum face area = 0.00152086. Maximum face area = 0.682333. Face area magnitudes OK. Min volume = 3.19342e05. Max volume = 0.158068. Total volume = 4547.61. Cell volumes OK. Mesh nonorthogonality Max: 56.2501 average: 14.9404 Nonorthogonality check OK. Face pyramids OK. Max skewness = 0.646766 OK. Coupled point location match (average 0) OK. Mesh OK. 1.jpg 2.jpg 3.jpg End Snapshots of mesh currently i am working with fixed time step. a dynamic time step is leading to very small time step. thanks 

October 20, 2014, 05:58 

#7 
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Fabian Roesler
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That's the point. you have to keep Co below 1 even if this leads to small dT. I see you have a tetMesh. So I'd increase the nonOrth correctors to 2 and use adjustTimeStep. This should solve your problems.
Cheers Fabian 

October 20, 2014, 06:17 

#8 
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Arjun
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Dear Fabian,
Currently working with adjusttimestep. time step in the order of e6....will update the results soon, Thanks Arjun 

October 21, 2014, 06:35 

#9 
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Arjun
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Dear Fabian,
Carried out simulations for 0.008 seconds. The results obtained are confusing. It looks like no flow have happened. velocity and pressure ranges are so high after 0.008 seconds. 4.jpg alpha 5.jpg pressure 6.jpg velocity I doubt some thing have gone wrong with the boundary condition. Please have a look at the B.C's posted in earlier comment. only variation made from above is that of outlet velocity where I have used OUTLET { type fluxCorrectedVelocity; phi phi; rho rho; } Since I am unsure of the velocity at outlet. Thanks in advance Arjun 

October 21, 2014, 07:33 

#10 
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Fabian Roesler
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Have you increased the nonOrth correctos? As you have a tet mesh you should adapt your fvSchemes and fvSolution. And moreover, as you have a small inlet velocity of 0.03 m/s, the phase will only travel 0.00024 m in the first 0.008 s. I guess your mesh is not that fine.


October 21, 2014, 07:42 

#11 
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Arjun
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Dear Fabian,
Yes I have increased the nNonOrthogonalCorrectors to 2. I agree that the time for which simulation have done is too low but why i am i getting high pressure and velocity range, also alpha is still appreciably negativeand becomes more negative with time step. Thanks in advance Arjun Last edited by Arjun Jayakumar; October 21, 2014 at 13:48. 

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