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January 7, 2014, 05:02 
Courantnumber explodes after a lon while (icoFoam)

#1 
New Member
Join Date: Jan 2014
Posts: 5
Rep Power: 4 
Hi,
I am new with openFoam and I am trying to simulate a turbinecascade with icoFoam. 0/p dimensions [0 2 2 0 0 0 0]; internalField uniform 5057.9; boundaryField { PERIODIC1 { type cyclic; } periodic_sh { type cyclic; } BLADE { type zeroGradient; } HUB { type zeroGradient; } INLET { type zeroGradient; } OUTLET { type advective; phi phi; value uniform 5057.9; } TIP { type zeroGradient; } } 0/u dimensions [0 1 1 0 0 0 0]; internalField uniform (30 30 0); boundaryField { PERIODIC1 { type cyclic; } periodic_sh { type cyclic; } BLADE { type fixedValue; value uniform (0 0 0); } HUB { type zeroGradient; } INLET { type fixedValue; value uniform (36.885 32.064 0); } OUTLET { type advective; phi phi; } TIP { type zeroGradient; } } controlDict application icoFoam; startFrom startTime; startTime 0.0001; stopAt endTime; endTime 0.01; deltaT 0.00000004; adjustTimeStep yes; // Or no writeControl adjustableRunTime; writeInterval 0.000005; purgeWrite 20; writeFormat ascii; writePrecision 9; writeCompression off; timeFormat general; timePrecision 9; runTimeModifiable yes; The first itterations are very good, but everytime at the same time in my case time=0.001 the Courantnumber explodes, after a day of simulation. Can someone help pls? 

January 13, 2014, 06:04 

#2 
New Member
Josh
Join Date: Jun 2013
Posts: 14
Rep Power: 5 
The best way I've found to debug these errors is to write the output at every time step (use purgeWrite if required) and analyse the 'results'. This should tell you if the courant number is caused by physically high velocities or not.


January 14, 2014, 06:34 

#4 
New Member
Join Date: Jan 2014
Posts: 5
Rep Power: 4 
Here are the last iterations:
Courant Number mean: 0.00135108479 max: 0.325747809 DILUPBiCG: Solving for Ux, Initial residual = 0.000560602417, Final residual = 4.03296652e08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.00015680267, Final residual = 4.9929129e09, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.000872529694, Final residual = 1.2753294e06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0333809278, Final residual = 0.00163371246, No Iterations 99 DICPCG: Solving for p, Initial residual = 0.00664221968, Final residual = 0.000316368199, No Iterations 191 DICPCG: Solving for p, Initial residual = 0.00265865953, Final residual = 0.000131461652, No Iterations 202 time step continuity errors : sum local = 5.62127726e11, global = 4.85646331e13, cumulative = 7.05936807e10 DICPCG: Solving for p, Initial residual = 0.00172637241, Final residual = 8.14285543e05, No Iterations 191 DICPCG: Solving for p, Initial residual = 0.000829504218, Final residual = 3.89580035e05, No Iterations 207 DICPCG: Solving for p, Initial residual = 0.000601586018, Final residual = 2.96378233e05, No Iterations 197 time step continuity errors : sum local = 1.26902051e11, global = 9.71962381e14, cumulative = 7.05839611e10 ExecutionTime = 313815.55 s ClockTime = 316731 s Time = 0.000130464 Courant Number mean: 0.00135142615 max: 0.365206875 DILUPBiCG: Solving for Ux, Initial residual = 0.000624335245, Final residual = 4.49943786e08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000173011857, Final residual = 8.25574465e09, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.000923101222, Final residual = 3.27248077e06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0343213889, Final residual = 0.00166055835, No Iterations 193 DICPCG: Solving for p, Initial residual = 0.00707040719, Final residual = 0.000339425603, No Iterations 100 DICPCG: Solving for p, Initial residual = 0.00245047902, Final residual = 0.000120873377, No Iterations 200 time step continuity errors : sum local = 5.52798683e11, global = 2.32304936e14, cumulative = 7.05862841e10 DICPCG: Solving for p, Initial residual = 0.00169495729, Final residual = 8.09930343e05, No Iterations 101 DICPCG: Solving for p, Initial residual = 0.000876530509, Final residual = 4.18015271e05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.000634705028, Final residual = 3.14877683e05, No Iterations 102 time step continuity errors : sum local = 1.44976153e11, global = 1.18459615e12, cumulative = 7.07047437e10 ExecutionTime = 313844.61 s ClockTime = 316760 s Time = 0.000130474 Courant Number mean: 0.00135182934 max: 0.413264518 DILUPBiCG: Solving for Ux, Initial residual = 0.000704629111, Final residual = 4.70605141e08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.0001940312, Final residual = 1.57881622e08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.000985879925, Final residual = 1.43045728e06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0325267583, Final residual = 0.00158705736, No Iterations 196 DICPCG: Solving for p, Initial residual = 0.00757949401, Final residual = 0.000378785221, No Iterations 108 DICPCG: Solving for p, Initial residual = 0.00280037641, Final residual = 0.000138433166, No Iterations 140 time step continuity errors : sum local = 6.85748798e11, global = 5.09917634e12, cumulative = 7.01948261e10 DICPCG: Solving for p, Initial residual = 0.00193374674, Final residual = 9.46097161e05, No Iterations 102 DICPCG: Solving for p, Initial residual = 0.00103330869, Final residual = 5.06354596e05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.000753501164, Final residual = 3.73602746e05, No Iterations 107 time step continuity errors : sum local = 1.86450563e11, global = 1.84520793e12, cumulative = 7.03793469e10 ExecutionTime = 313872.26 s ClockTime = 316787 s Time = 0.000130484 Courant Number mean: 0.00135231156 max: 0.472290254 DILUPBiCG: Solving for Ux, Initial residual = 0.000808944526, Final residual = 4.92679153e08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000220969293, Final residual = 2.50528429e08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00106574013, Final residual = 1.5683862e06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0322361377, Final residual = 0.00152126195, No Iterations 198 DICPCG: Solving for p, Initial residual = 0.00820591951, Final residual = 0.000407452729, No Iterations 111 DICPCG: Solving for p, Initial residual = 0.00314755933, Final residual = 0.000155705809, No Iterations 139 time step continuity errors : sum local = 8.46944469e11, global = 6.48447628e12, cumulative = 6.97308993e10 DICPCG: Solving for p, Initial residual = 0.0021942357, Final residual = 0.000101660495, No Iterations 103 DICPCG: Solving for p, Initial residual = 0.00118636758, Final residual = 5.76171022e05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.000863136193, Final residual = 4.25000504e05, No Iterations 106 time step continuity errors : sum local = 2.33183295e11, global = 2.26961477e12, cumulative = 6.99578608e10 ExecutionTime = 313900.13 s ClockTime = 316815 s Time = 0.000130494 Courant Number mean: 0.00135289441 max: 0.545196474 DILUPBiCG: Solving for Ux, Initial residual = 0.000941724687, Final residual = 5.49792424e08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000255768375, Final residual = 3.89239595e08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00116950018, Final residual = 2.21858032e06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0337740886, Final residual = 0.00168285777, No Iterations 198 DICPCG: Solving for p, Initial residual = 0.00916882678, Final residual = 0.000445192936, No Iterations 112 DICPCG: Solving for p, Initial residual = 0.00356657676, Final residual = 0.000174221061, No Iterations 140 time step continuity errors : sum local = 1.05861353e10, global = 8.43363183e12, cumulative = 6.91144976e10 DICPCG: Solving for p, Initial residual = 0.00248973046, Final residual = 0.000117714068, No Iterations 103 DICPCG: Solving for p, Initial residual = 0.00135836735, Final residual = 6.70189108e05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.000989233567, Final residual = 4.88439898e05, No Iterations 106 time step continuity errors : sum local = 2.99826103e11, global = 2.88323813e12, cumulative = 6.94028214e10 ExecutionTime = 313928.19 s ClockTime = 316844 s Time = 0.000130504 Courant Number mean: 0.00135360692 max: 0.635173148 DILUPBiCG: Solving for Ux, Initial residual = 0.00111241783, Final residual = 6.75475301e08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000301108451, Final residual = 5.68671287e08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00130073141, Final residual = 3.66935785e06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0349797822, Final residual = 0.00170827006, No Iterations 200 DICPCG: Solving for p, Initial residual = 0.00970473193, Final residual = 0.000463780216, No Iterations 112 DICPCG: Solving for p, Initial residual = 0.0037789092, Final residual = 0.000183773907, No Iterations 140 time step continuity errors : sum local = 1.26279482e10, global = 1.0214584e11, cumulative = 6.8381363e10 DICPCG: Solving for p, Initial residual = 0.00268332084, Final residual = 0.000132464647, No Iterations 102 DICPCG: Solving for p, Initial residual = 0.00145297631, Final residual = 7.13565785e05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.00105976862, Final residual = 5.2285137e05, No Iterations 106 time step continuity errors : sum local = 3.63288792e11, global = 3.45070742e12, cumulative = 6.87264337e10 ExecutionTime = 313963.62 s ClockTime = 316880 s Time = 0.000130514 Courant Number mean: 0.00135448235 max: 0.744505284 DILUPBiCG: Solving for Ux, Initial residual = 0.00132165459, Final residual = 8.89449741e08, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000357101994, Final residual = 8.05188377e08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00145279054, Final residual = 6.88082683e06, No Iterations 1 DICPCG: Solving for p, Initial residual = 0.0371526458, Final residual = 0.0018550487, No Iterations 200 DICPCG: Solving for p, Initial residual = 0.00989807886, Final residual = 0.000481242641, No Iterations 110 DICPCG: Solving for p, Initial residual = 0.00380425511, Final residual = 0.000190083233, No Iterations 139 time step continuity errors : sum local = 1.4780888e10, global = 1.14090625e11, cumulative = 6.75855275e10 DICPCG: Solving for p, Initial residual = 0.0027571914, Final residual = 0.000137054566, No Iterations 101 DICPCG: Solving for p, Initial residual = 0.00147465605, Final residual = 7.02733199e05, No Iterations 202 DICPCG: Solving for p, Initial residual = 0.00107328549, Final residual = 5.31538962e05, No Iterations 106 time step continuity errors : sum local = 4.18094633e11, global = 4.06678558e12, cumulative = 6.7992206e10 ExecutionTime = 313991.65 s ClockTime = 316908 s Time = 0.000130524 Courant Number mean: 0.00135554523 max: 0.870939992 DILUPBiCG: Solving for Ux, Initial residual = 0.00156394584, Final residual = 1.14334821e07, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000421740246, Final residual = 1.02036997e07, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00161100897, Final residual = 3.99879114e07, No Iterations 2 DICPCG: Solving for p, Initial residual = 0.0384808651, Final residual = 0.00179635437, No Iterations 196 DICPCG: Solving for p, Initial residual = 0.00919366901, Final residual = 0.000445499412, No Iterations 101 DICPCG: Solving for p, Initial residual = 0.00331579402, Final residual = 0.000163210372, No Iterations 140 time step continuity errors : sum local = 1.40648799e10, global = 9.43821672e12, cumulative = 6.70483844e10 DICPCG: Solving for p, Initial residual = 0.002405895, Final residual = 0.000117504712, No Iterations 100 DICPCG: Solving for p, Initial residual = 0.00124074764, Final residual = 5.87632053e05, No Iterations 201 DICPCG: Solving for p, Initial residual = 0.000903733201, Final residual = 4.4399401e05, No Iterations 106 time step continuity errors : sum local = 3.86305268e11, global = 3.74852639e12, cumulative = 6.7423237e10 ExecutionTime = 314019.16 s ClockTime = 316936 s Time = 0.000130534 Courant Number mean: 0.00135679454 max: 0.998997938 DILUPBiCG: Solving for Ux, Initial residual = 0.00179656253, Final residual = 1.25723893e07, No Iterations 1 DILUPBiCG: Solving for Uy, Initial residual = 0.000481528948, Final residual = 7.05450051e08, No Iterations 1 DILUPBiCG: Solving for Uz, Initial residual = 0.00172289179, Final residual = 1.35426585e07, No Iterations 2 DICPCG: Solving for p, Initial residual = 0.0414029784, Final residual = 0.00200185089, No Iterations 31 DICPCG: Solving for p, Initial residual = 0.0083390347, Final residual = 0.000379814079, No Iterations 191 DICPCG: Solving for p, Initial residual = 0.00253898182, Final residual = 0.000115853871, No Iterations 203 time step continuity errors : sum local = 1.03571708e10, global = 1.46157115e12, cumulative = 6.72770799e10 DICPCG: Solving for p, Initial residual = 0.00160164772, Final residual = 7.44660037e05, No Iterations 193 DICPCG: Solving for p, Initial residual = 0.000650163566, Final residual = 3.19850235e05, No Iterations 203 DICPCG: Solving for p, Initial residual = 0.000390252354, Final residual = 1.85219341e05, No Iterations 200 time step continuity errors : sum local = 1.65702356e11, global = 3.69269402e14, cumulative = 6.72807726e10 ExecutionTime = 314051.67 s ClockTime = 316969 s I started the simulation with a program which controls and configure the courantnumber (C<0.2), but the solution is also bad after a while. The pressure and the velocity value explodes at the trailingedge e.g. pressure=9e+156 and velocity=10000 m/s ??? 

January 14, 2014, 13:56 

#5  
Senior Member
Tobias Holzmann
Join Date: Oct 2010
Location: Leoben (Austria)
Posts: 1,504
Blog Entries: 6
Rep Power: 26 
Quote:
You are using a fixed dt now ? 

January 14, 2014, 21:54 

#6  
New Member
Josh
Join Date: Jun 2013
Posts: 14
Rep Power: 5 
Quote:
I do see now however that your run time is fairly large so you may want to wait for someone who knows a bit more than me to identify your issue without rerunning. 

January 29, 2014, 05:27 

#7 
New Member
Join Date: Jan 2014
Posts: 5
Rep Power: 4 
I think the Problem was, that i got velocity over 1000 m/s at the outlet cause of a eddy....
I start the simulation with simpleFoam and use the solution for icoFoam. Now it works fine. Thanks 

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