PIMPLE Stability

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 July 11, 2022, 05:31 PIMPLE Stability #1 Member   Callum Guy Join Date: Dec 2019 Location: Scotland Posts: 44 Rep Power: 6 Morning Foamers, I'm running into some stability issue when using interFOAM. My simulations crash at a similar time, consistently with a spike in "time step continuity errors" and the p_rgh residual. Here's the log of the last 2 timesteps computed: Code: ```Courant Number mean: 0.0230739546284 max: 38.197898741 Interface Courant Number mean: 0.000777623464901 max: 3.81051460639 Time = 14.88 PIMPLE: iteration 1 alpha.water BC on patch outlet MULES: Solving for alpha.water alpha.water BC on patch outlet Phase-1 volume fraction = 0.83627896636 Min(alpha.water) = -103.911816209 Max(alpha.water) = 150.52296902 alpha.water BC on patch outlet MULES: Solving for alpha.water alpha.water BC on patch outlet Phase-1 volume fraction = 0.836269635433 Min(alpha.water) = -487.723760213 Max(alpha.water) = 508.484315717 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.174349102868 ) Velocity BC on patch outlet Force on turbine.blade1: (187539.627186 -54603.0964318 -9212.78760151) Force on turbine.blade2: (196564.813807 20542.1016411 55167.9807565) Force on turbine.blade3: (194943.762771 37863.6903348 -45806.9159198) Force on turbine.hub: (5490.2140389 -17.5086780725 -2.9541132794) Force on turbine.tower: (0 0 0) Azimuthal angle (degrees) of turbine: 1250.42309209 Tip speed ratio of turbine: 4.4 Power coefficient from turbine: 0.400091257429 Rotor drag coefficient from turbine: 0.496560923074 DICPCG: Solving for p_rgh, Initial residual = 0.0021608988582, Final residual = 0.000107723848319, No Iterations 137 time step continuity errors : sum local = 7.17961468072e-05, global = 2.95478051822e-06, cumulative = 4.04354720138e-05 DICPCG: Solving for p_rgh, Initial residual = 0.000874326709373, Final residual = 4.33039666109e-05, No Iterations 55 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.174349102868 ) Velocity BC on patch outlet time step continuity errors : sum local = 2.01227742579e-05, global = -2.21184730262e-06, cumulative = 3.82236247112e-05 DICPCG: Solving for p_rgh, Initial residual = 0.000263194372774, Final residual = 9.86553797461e-08, No Iterations 246 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.174349102868 ) Velocity BC on patch outlet time step continuity errors : sum local = 4.53912356615e-08, global = -1.17322367952e-09, cumulative = 3.82224514876e-05 smoothSolver: Solving for omega, Initial residual = 0.974553445026, Final residual = 2.66883818386e-09, No Iterations 4 bounding omega, min: -116729.189533 max: 1019378.79645 average: 1.02686841445 smoothSolver: Solving for k, Initial residual = 0.0188624168182, Final residual = 8.87519932106e-09, No Iterations 7 bounding k, min: -0.285459700159 max: 77.7821249136 average: 0.166107013953 ExecutionTime = 44122.8 s ClockTime = 45602 s Courant Number mean: 0.0299350494335 max: 2595.75221681 Interface Courant Number mean: 0.000886954295052 max: 492.131273028 Time = 14.885 PIMPLE: iteration 1 alpha.water BC on patch outlet MULES: Solving for alpha.water alpha.water BC on patch outlet Phase-1 volume fraction = 0.836256700009 Min(alpha.water) = -25094.9966241 Max(alpha.water) = 58362.3120119 alpha.water BC on patch outlet MULES: Solving for alpha.water alpha.water BC on patch outlet Phase-1 volume fraction = 0.836279047236 Min(alpha.water) = -9077126.4279 Max(alpha.water) = 14835489.7555 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.173966510369 ) Velocity BC on patch outlet Force on turbine.blade1: (190766.74839 -56216.7106176 -9061.56576385) Force on turbine.blade2: (199941.439777 21420.881685 56262.8625324) Force on turbine.blade3: (196785.248964 38285.0426242 -47014.532404) Force on turbine.hub: (5616.86786532 -28.3566064197 -4.57079845279) Force on turbine.tower: (0 0 0) Azimuthal angle (degrees) of turbine: 1250.84326114 Tip speed ratio of turbine: 4.4 Power coefficient from turbine: 0.410282425887 Rotor drag coefficient from turbine: 0.503842675799 DICPCG: Solving for p_rgh, Initial residual = 0.128588696877, Final residual = 0.00624445596319, No Iterations 10 time step continuity errors : sum local = 0.00339774178095, global = -0.00075871394595, cumulative = -0.000720491494463 DICPCG: Solving for p_rgh, Initial residual = 0.000102330247987, Final residual = 4.96600582123e-06, No Iterations 47 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.173966510369 ) Velocity BC on patch outlet time step continuity errors : sum local = 0.00236246879967, global = -0.000305604529903, cumulative = -0.00102609602437 DICPCG: Solving for p_rgh, Initial residual = 0.00172681281545, Final residual = 9.99392623372e-08, No Iterations 283 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.173966510369 ) Velocity BC on patch outlet time step continuity errors : sum local = 3.61463698303e-06, global = 1.01674220237e-07, cumulative = -0.00102599435015 smoothSolver: Solving for omega, Initial residual = 0.987600465769, Final residual = 5.33850547774e-10, No Iterations 5 bounding omega, min: -24776085.4187 max: 19488036.3905 average: 297.211121357 smoothSolver: Solving for k, Initial residual = 0.323487262889, Final residual = 3.95184347366e-10, No Iterations 5 bounding k, min: -16.8027050907 max: 340.826867446 average: 0.173334322987 ExecutionTime = 44152.98 s ClockTime = 45633 s Courant Number mean: 0.305307922727 max: 132545.752862 Interface Courant Number mean: 0.0215072865315 max: 67758.6521143 Time = 14.89 PIMPLE: iteration 1 alpha.water BC on patch outlet MULES: Solving for alpha.water alpha.water BC on patch outlet Phase-1 volume fraction = 0.836342658454 Min(alpha.water) = -121965323191 Max(alpha.water) = 109107175275 alpha.water BC on patch outlet MULES: Solving for alpha.water alpha.water BC on patch outlet Phase-1 volume fraction = 0.836443830625 Min(alpha.water) = -2.88802783634e+15 Max(alpha.water) = 3.70574224922e+15 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.170576529572 ) Velocity BC on patch outlet Force on turbine.blade1: (130484.732008 -30988.2423986 -4762.11120066) Force on turbine.blade2: (145017.627717 14414.2680683 37040.5235279) Force on turbine.blade3: (147517.277377 21830.9336265 -27213.8447653) Force on turbine.hub: (3525.59840819 172.044707896 26.4389319004) Force on turbine.tower: (0 0 0) Azimuthal angle (degrees) of turbine: 1251.26343019 Tip speed ratio of turbine: 4.4 Power coefficient from turbine: 0.236732734963 Rotor drag coefficient from turbine: 0.362346920966 DICPCG: Solving for p_rgh, Initial residual = 0.990013676426, Final residual = 0.0468017350473, No Iterations 9 time step continuity errors : sum local = 1488.54503318, global = -1.00783303658, cumulative = -1.00885903093 DICPCG: Solving for p_rgh, Initial residual = 1.75086191517e-09, Final residual = 1.75086191517e-09, No Iterations 0 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.170576529572 ) Velocity BC on patch outlet time step continuity errors : sum local = 46881.4838944, global = 3911.99295226, cumulative = 3910.98409323 DICPCG: Solving for p_rgh, Initial residual = 6.42535826912e-07, Final residual = 9.55799719526e-08, No Iterations 3 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.170576529572 ) Velocity BC on patch outlet time step continuity errors : sum local = 2559272.92531, global = -2526707.8432, cumulative = -2522796.85911 smoothSolver: Solving for omega, Initial residual = 2.56912167053e-09, Final residual = 2.56912167053e-09, No Iterations 0 smoothSolver: Solving for k, Initial residual = 0.703176894591, Final residual = 5.4883346337e-09, No Iterations 4 bounding k, min: -19.5825745916 max: 269.992183381 average: 0.17543350682 ExecutionTime = 44162.24 s ClockTime = 45642 s Courant Number mean: 44580578.5106 max: 3.53003684885e+13 Interface Courant Number mean: 968604.38205 max: 1.59633194071e+12 Time = 14.895 PIMPLE: iteration 1 alpha.water BC on patch outlet MULES: Solving for alpha.water alpha.water BC on patch outlet Phase-1 volume fraction = -15937010.9633 Min(alpha.water) = -1.57713761489e+26 Max(alpha.water) = 2.9516660853e+26 alpha.water BC on patch outlet MULES: Solving for alpha.water alpha.water BC on patch outlet Phase-1 volume fraction = -5.35687774577e+26 Min(alpha.water) = -3.63322160331e+50 Max(alpha.water) = 3.6404095442e+50 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.164308556659 ) Velocity BC on patch outlet Force on turbine.blade1: (51631.2434405 -7756.81430588 -1133.86454448) Force on turbine.blade2: (86866.2801199 7465.43665384 18775.4561849) Force on turbine.blade3: (68488.8431049 4582.28635569 -5798.76745035) Force on turbine.hub: (1779.66085343 254.583462175 37.214138432) Force on turbine.tower: (0 0 0) Azimuthal angle (degrees) of turbine: 1251.68359924 Tip speed ratio of turbine: 4.4 Power coefficient from turbine: 0.0797832917607 Rotor drag coefficient from turbine: 0.177345146484 DICPCG: Solving for p_rgh, Initial residual = 0.0369707537481, Final residual = 0.00136598026531, No Iterations 8 time step continuity errors : sum local = 1.79053436895e+15, global = -12368703537, cumulative = -12371226333.8 DICPCG: Solving for p_rgh, Initial residual = 4.68463524854e-24, Final residual = 4.68463524854e-24, No Iterations 0 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.164308556659 ) Velocity BC on patch outlet time step continuity errors : sum local = 5.86444782243e+25, global = -2.76694252135e+25, cumulative = -2.76694252135e+25 DICPCG: Solving for p_rgh, Initial residual = 0.999999978708, Final residual = 4.72823569472e-07, No Iterations 1000 3D_2D Absorption BC on patch inlet "Correction Levels" 1( -0.164308556659 ) Velocity BC on patch outlet time step continuity errors : sum local = 2.77996096845e+50, global = -7.60357064878e+48, cumulative = -7.60357064878e+48 [3] #0 Foam::error::printStack(Foam::Ostream&) at ??:? [3] #1 Foam::sigFpe::sigHandler(int) at ??:? [3] #2 ? in /lib64/libc.so.6 [3] #3 Foam::symGaussSeidelSmoother::smooth(Foam::word const&, Foam::Field&, Foam::lduMatrix const&, Foam::Field const&, Foam::FieldField const&, Foam::UPtrList const&, unsigned char, int) at ??:? [3] #4 Foam::symGaussSeidelSmoother::scalarSmooth(Foam::Field&, Foam::Field const&, unsigned char, int) const at ??:? [3] #5 Foam::symGaussSeidelSmoother::smooth(Foam::Field&, Foam::Field const&, unsigned char, int) const at ??:? [3] #6 Foam::smoothSolver::solve(Foam::Field&, Foam::Field const&, unsigned char) const at ??:? [3] #7 Foam::fvMatrix::solveSegregated(Foam::dictionary const&) at ??:? [3] #8 Foam::fvMatrix::solveSegregatedOrCoupled(Foam::dictionary const&) at ??:? [3] #9 Foam::fvMesh::solve(Foam::fvMatrix&, Foam::dictionary const&) const at ??:? [3] #10 Foam::SolverPerformance Foam::solve(Foam::tmp > const&) at ??:? [3] #11 Foam::kOmegaSSTStable > >, Foam::IncompressibleTurbulenceModel >::correct() at ??:? [3] #12 ? at ??:? [3] #13 __libc_start_main in /lib64/libc.so.6 [3] #14 ? at ??:? [node1h30:26068] *** Process received signal *** [node1h30:26068] Signal: Floating point exception (8) [node1h30:26068] Signal code: (-6) [node1h30:26068] Failing at address: 0x162292000065d4 [node1h30:26068] [ 0] /lib64/libc.so.6(+0x36400)[0x2b25a4d31400] [node1h30:26068] [ 1] /lib64/libc.so.6(gsignal+0x37)[0x2b25a4d31387] [node1h30:26068] [ 2] /lib64/libc.so.6(+0x36400)[0x2b25a4d31400] [node1h30:26068] [ 3] /exports/applications/apps/community/eng/OpenFOAM-1912/OpenFOAM-v1912/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZN4Foam22symGaussSeidelSmoother6smoothERKNS_4wordERNS_5FieldIdEERKNS_9lduMatrixERKS5_RKNS_10FieldFieldIS4_dEERKNS_8UPtrListIKNS_17lduInterfaceFieldEEEhi+0x32d)[0x2b25a3bf99ed] [node1h30:26068] [ 4] /exports/applications/apps/community/eng/OpenFOAM-1912/OpenFOAM-v1912/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZNK4Foam22symGaussSeidelSmoother12scalarSmoothERNS_5FieldIdEERKS2_hi+0x2d)[0x2b25a3bf9c2d] [node1h30:26068] [ 5] /exports/applications/apps/community/eng/OpenFOAM-1912/OpenFOAM-v1912/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZNK4Foam22symGaussSeidelSmoother6smoothERNS_5FieldIdEERKS2_hi+0xd)[0x2b25a3bf968d] [node1h30:26068] [ 6] /exports/applications/apps/community/eng/OpenFOAM-1912/OpenFOAM-v1912/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZNK4Foam12smoothSolver5solveERNS_5FieldIdEERKS2_h+0x5ac)[0x2b25a3bf12ac] [node1h30:26068] [ 7] /exports/applications/apps/community/eng/OpenFOAM-1912/OpenFOAM-v1912/platforms/linux64GccDPInt32Opt/lib/libfiniteVolume.so(_ZN4Foam8fvMatrixIdE15solveSegregatedERKNS_10dictionaryE+0x11f)[0x2b259f79216f] [node1h30:26068] [ 8] /exports/applications/apps/community/eng/OpenFOAM-1912/OpenFOAM-v1912/platforms/linux64GccDPInt32Opt/lib/libfiniteVolume.so(_ZN4Foam8fvMatrixIdE24solveSegregatedOrCoupledERKNS_10dictionaryE+0x27f)[0x2b259f0e6fef] [node1h30:26068] [ 9] /exports/applications/apps/community/eng/OpenFOAM-1912/OpenFOAM-v1912/platforms/linux64GccDPInt32Opt/lib/libfiniteVolume.so(_ZNK4Foam6fvMesh5solveERNS_8fvMatrixIdEERKNS_10dictionaryE+0xf)[0x2b259f0a93bf] [node1h30:26068] [10] /exports/applications/apps/community/eng/OpenFOAM-1912/OpenFOAM-v1912/platforms/linux64GccDPInt32Opt/lib/libincompressibleTurbulenceModels.so(_ZN4Foam5solveIdEENS_17SolverPerformanceIT_EERKNS_3tmpINS_8fvMatrixIS2_EEEE+0x126)[0x2b25a2e12ba6] [node1h30:26068] [11] /home/s1453918/OpenFOAM/s1453918-v1912/platforms/linux64GccDPInt32Opt/lib/libturbulenceMultiphaseOlaFlowModels.so(_ZN4Foam15kOmegaSSTStableINS_13eddyViscosityINS_8RASModelINS_29IncompressibleTurbulenceModelINS_14transportModelEEEEEEES5_E7correctEv+0xd1a)[0x2b25bd66b71a] [node1h30:26068] [12] olaFlow_current[0x444050] [node1h30:26068] [13] /lib64/libc.so.6(__libc_start_main+0xf5)[0x2b25a4d1d555] [node1h30:26068] [14] olaFlow_current[0x4490c5] [node1h30:26068] *** End of error message *** [node1h27][[33322,1],35][btl_tcp_frag.c:237:mca_btl_tcp_frag_recv] mca_btl_tcp_frag_recv: readv failed: Connection reset by peer (104) [node1h27][[33322,1],34][btl_tcp_frag.c:237:mca_btl_tcp_frag_recv] mca_btl_tcp_frag_recv: readv failed: Connection reset by peer (104) [node1h31][[33322,1],19][btl_tcp_frag.c:237:mca_btl_tcp_frag_recv] mca_btl_tcp_frag_recv: readv failed: Connection reset by peer (104) [node1h27][[33322,1],32][btl_tcp_frag.c:237:mca_btl_tcp_frag_recv] mca_btl_tcp_frag_recv: readv failed: Connection reset by peer (104) -------------------------------------------------------------------------- mpirun noticed that process rank 3 with PID 26068 on node node1h30 exited on signal 8 (Floating point exception). --------------------------------------------------------------------------``` and a copy of my fvSolution dictionary: Code: ```/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 2.3.0 | | \\ / A nd | Web: www.OpenFOAM.org | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; location "system"; object fvSolution; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // solvers { "alpha.water.*" { nAlphaCorr 1; nAlphaSubCycles 2; alphaOuterCorrectors yes; cAlpha 1; MULESCorr no; nLimiterIter 3; solver smoothSolver; smoother symGaussSeidel; tolerance 1e-8; relTol 0; } "pcorr.*" { solver PCG; preconditioner DIC; tolerance 1e-5; relTol 0; } p_rgh { solver PCG; preconditioner DIC; tolerance 1e-07; relTol 0.05; } p_rghFinal { \$p_rgh; relTol 0; } U { solver smoothSolver; smoother symGaussSeidel; tolerance 1e-06; relTol 0; } "(k|epsilon|omega|B|nuTilda).*" { solver smoothSolver; smoother symGaussSeidel; tolerance 1e-08; relTol 0; } } PIMPLE { momentumPredictor no; nOuterCorrectors 1; nCorrectors 3; nNonOrthogonalCorrectors 0; } relaxationFactors { fields { } equations { ".*" 1; } } // ************************************************************************* //``` It's also noteworthy that my timestep is fixed at 0.005 i.e. adjustTimeStep set to no. Also puzzling (to me) is that the line Code: `Phase-1 volume fraction = XXXXXXX Min(alpha.water) = XXXXXXX Max(alpha.water) = XXXXXXX` is consistently out of the [0,1] bounds, throughout the simulation, though when "stable" it's outside the bounds by a very tiny amount. Does anyonne have any wisdom they could share on any of the above? Cheers, Callum

 July 15, 2022, 05:20 #2 New Member   Join Date: Jul 2022 Posts: 6 Rep Power: 3 You either have 1) a bad set of BCs, 2) bad quality mesh or 3) both 1) and 2). Turn on the adjustTimeStep and see how the solver behaves (if the time step keeps getting smaller, think about whether the velocity in BC is reasonable). The mean courant number is not tiny compared to the max one so your mesh is probably not too fine throughout. Check the boundary layers and boundary conditions.

July 15, 2022, 06:26
#3
Member

Callum Guy
Join Date: Dec 2019
Location: Scotland
Posts: 44
Rep Power: 6
Hey Passenger,

I appreciate the reply. I expect the BC's are good because they are from olaFlow and run incredibly well in similar cases.

The mesh is essentially an empty rectangle that has refinement regions at the top and in the centre (I apply body forces there) with a non-orthogonality of <25, so I'm at pains to describe it as "bad quality" (I've attached a picture of a course version of the mesh).

An update on this is that I've successfully completed the simulation on a coarser mesh. Leading me to believe it's CFL related. So I'm currently in the process of testing at a lesser delta T (0.0025) which has surpassed the previous fail point. I am equally testing another version where I have upped maxCo to 2.0 and maxAlphaCo to 1.0. To hopefully make my simulations more efficient, I have enabled the adjustable time step for the new delta T, but I am limited as I need high(ish) frequency outputs.

All the best,
Callum
Attached Images
 mesh.jpg (78.5 KB, 15 views)

 July 16, 2022, 04:17 #4 New Member   Join Date: Jul 2022 Posts: 6 Rep Power: 3 Hi Callum, The problem I have with CFL is similar to yours, that the BC and mesh quality is both good while the max Courant number is much larger than 1. The mean Courant number in my case is generally less than 0.01 but I still need to use adjustTimeStep to keep max Courant number at a low level. This gives me a time step at ~ 10^-5 s and it's a long simulation even for a case with 2s time span. I think it's possible to pin point where the max Courant number occurs and adjust the mesh accordingly but I'm not there yet. My wild guess is the no-slip wall near the velocity inlet and the boundary layers are too fine.

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