High time step continuity errors when activating RAS model

smhk · August 24, 2024, 18:06

Hey everyone,
I'm currently trying to run a simulation for a Francis turbine with a draft tube. The simulation seems a bit complex, so I attempted to simplify it by following the instructions in the manual... . It states that I should run it with 10% of the inlet velocity in the initial 1000 iterations, and it should converge under these conditions. However, I encountered a problem. When I activated the RAS models in the RAS properties, after about 10 iterations, I got "time step continuity errors : sum local = 1.07134e+102, global = -2.81893e+85, cumulative = -2.81893e+85 Floating point exception". On the other hand, when using the laminar model, the results seemed better with much lower time step continuity errors.
I want to understand how this has happened and how I can solve it. Thank you

here are the logs:

RAS :kEpsilon

Code:

Time = 165

BiCGStab:  Solving for Ux, Initial residual = 0.0430624, Final residual = 5.53254e-08, No Iterations 1
BiCGStab:  Solving for Uy, Initial residual = 1, Final residual = 2.92474e-06, No Iterations 1
BiCGStab:  Solving for Uz, Initial residual = 1, Final residual = 3.29756e-06, No Iterations 1
BiCGStab:  Solving for p, Initial residual = 0.644021, Final residual = 0.000519356, No Iterations 2
time step continuity errors : sum local = 2.61097e+18, global = -3.80043e+14, cumulative = -3.80042e+14
BiCGStab:  Solving for epsilon, Initial residual = 0.999998, Final residual = 1.08264e-08, No Iterations 1
bounding epsilon, min: -4.80646e+16 max: 3.07812e+36 average: 2.14493e+30
BiCGStab:  Solving for k, Initial residual = 1, Final residual = 5.86534e-09, No Iterations 1
bounding k, min: -7.58275e+11 max: 2.65872e+34 average: 1.58172e+28
ExecutionTime = 80.02 s  ClockTime = 88 s

Checking flux phi GGI balance.
Cyclic GGI pair (RU_PER2_31, RU_PER1_32)
Area: 0.00419516 0.00419517 Diff = -7.21973e-09 or 0.000172096 %
Flux: 7.76981e+11 7.76898e+11 Diff = 8.35261e+07 or 0.0107501 %
Cyclic GGI pair (RU_PER2_40, RU_PER1_41)
Area: 0.000282615 0.00028262 Diff = -5.36601e-09 or 0.00189866 %
Flux: 7.66028e+07 7.66173e+07 Diff = -14555.4 or 0.0189976 %
Cyclic GGI pair (RU_PER2_48, RU_PER1_49)
Area: 0.00188188 0.00188187 Diff = 9.59111e-09 or 0.000509656 %
Flux: 2.66571e+10 2.66492e+10 Diff = -7.90056e+06 or 0.0296377 %
Cyclic GGI pair (RU_PER2_52, RU_PER1_53)
Area: 0.000273776 0.000273778 Diff = -2.61869e-09 or 0.000956501 %
Flux: 2.44707e+07 2.49216e+07 Diff = -450856 or 1.8091 %
Cyclic GGI pair (RU_PER2_54, RU_PER1_55)
Area: 0.0357119 0.0357119 Diff = 1.63478e-08 or 4.57768e-05 %
Flux: 2.20763e+14 2.09007e+14 Diff = -4.2977e+14 or 194.675 %
Cyclic GGI pair (GV_PER2_4, GV_PER1_5)
Area: 0.000768029 0.000767998 Diff = 3.08771e-08 or 0.00402031 %
Flux: 748584 752135 Diff = 3551.36 or 0.472171 %
Cyclic GGI pair (GV_PER2_12, GV_PER1_13)
Area: 0.000731156 0.000731155 Diff = 1.86157e-10 or 2.54606e-05 %
Flux: 8.69247e+08 8.69228e+08 Diff = -18995.8 or 0.00218532 %
Cyclic GGI pair (GV_PER2_22, GV_PER1_23)
Area: 0.00409702 0.00409704 Diff = -2.41303e-08 or 0.000588969 %
Flux: 3.95316e+15 3.96387e+15 Diff = 1.07112e+13 or 0.27022 %
Time = 166

BiCGStab:  Solving for Ux, Initial residual = 0.099913, Final residual = 7.00287e-07, No Iterations 1
BiCGStab:  Solving for Uy, Initial residual = 1, Final residual = 9.87184e-09, No Iterations 1
BiCGStab:  Solving for Uz, Initial residual = 1, Final residual = 3.6444e-08, No Iterations 1
BiCGStab:  Solving for p, Initial residual = 1, Final residual = 0.00124421, No Iterations 3
time step continuity errors : sum local = 2.73229e+41, global = -6.43621e+34, cumulative = -6.43621e+34
BiCGStab:  Solving for epsilon, Initial residual = 1, Final residual = 1.99771e-09, No Iterations 1
bounding epsilon, min: -1.97648e+48 max: 7.18412e+56 average: 6.01793e+50
BiCGStab:  Solving for k, Initial residual = 1, Final residual = 2.04399e-05, No Iterations 1
bounding k, min: -9.94425e+23 max: 6.87835e+58 average: 8.26532e+52
ExecutionTime = 88.46 s  ClockTime = 97 s

Checking flux phi GGI balance.
Cyclic GGI pair (RU_PER2_31, RU_PER1_32)
Area: 0.00419516 0.00419517 Diff = -7.21973e-09 or 0.000172096 %
Flux: 9.13246e+19 9.1275e+19 Diff = -4.95661e+16 or 0.0542746 %
Cyclic GGI pair (RU_PER2_40, RU_PER1_41)
Area: 0.000282615 0.00028262 Diff = -5.36601e-09 or 0.00189866 %
Flux: 1.68383e+17 1.68416e+17 Diff = 3.29187e+13 or 0.019546 %
Cyclic GGI pair (RU_PER2_48, RU_PER1_49)
Area: 0.00188188 0.00188187 Diff = 9.59111e-09 or 0.000509656 %
Flux: 2.86436e+19 2.87056e+19 Diff = -6.19451e+16 or 0.215795 %
Cyclic GGI pair (RU_PER2_52, RU_PER1_53)
Area: 0.000273776 0.000273778 Diff = -2.61869e-09 or 0.000956501 %
Flux: 5.81866e+18 5.82042e+18 Diff = 1.76385e+15 or 0.0303045 %
Cyclic GGI pair (RU_PER2_54, RU_PER1_55)
Area: 0.0357119 0.0357119 Diff = 1.63478e-08 or 4.57768e-05 %
Flux: 3.47802e+25 3.33555e+25 Diff = 1.4247e+24 or 4.0963 %
Cyclic GGI pair (GV_PER2_4, GV_PER1_5)
Area: 0.000768029 0.000767998 Diff = 3.08771e-08 or 0.00402031 %
Flux: 4.5722e+17 4.54311e+17 Diff = -2.90872e+15 or 0.636176 %
Cyclic GGI pair (GV_PER2_12, GV_PER1_13)
Area: 0.000731156 0.000731155 Diff = 1.86157e-10 or 2.54606e-05 %
Flux: 1.15102e+23 9.96905e+22 Diff = -1.54119e+22 or 13.3897 %
Cyclic GGI pair (GV_PER2_22, GV_PER1_23)
Area: 0.00409702 0.00409704 Diff = -2.41303e-08 or 0.000588969 %
Flux: 1.60192e+36 1.53095e+36 Diff = -7.09691e+34 or 4.43026 %
Time = 167

BiCGStab:  Solving for Ux, Initial residual = 0.0997888, Final residual = 3.11555e-07, No Iterations 1
BiCGStab:  Solving for Uy, Initial residual = 1, Final residual = 6.91844e-08, No Iterations 1
BiCGStab:  Solving for Uz, Initial residual = 1, Final residual = 6.00344e-08, No Iterations 1
BiCGStab:  Solving for p, Initial residual = 1, Final residual = 2.55496e-05, No Iterations 2
time step continuity errors : sum local = 1.07134e+102, global = -2.81893e+85, cumulative = -2.81893e+85
Floating point exception

laminar:

Code:

Time = 157

BiCGStab:  Solving for Ux, Initial residual = 0.00273733, Final residual = 4.17662e-09, No Iterations 1
BiCGStab:  Solving for Uy, Initial residual = 0.00367481, Final residual = 1.69035e-08, No Iterations 1
BiCGStab:  Solving for Uz, Initial residual = 0.00921743, Final residual = 1.04403e-08, No Iterations 1
BiCGStab:  Solving for p, Initial residual = 0.00396223, Final residual = 2.81292e-05, No Iterations 746
time step continuity errors : sum local = 0.00975311, global = -0.000357865, cumulative = 0.106666
ExecutionTime = 2978.68 s  ClockTime = 3005 s

Checking flux phi GGI balance.
Cyclic GGI pair (RU_PER2_31, RU_PER1_32)
Area: 0.00419516 0.00419517 Diff = -7.21973e-09 or 0.000172096 %
Flux: 0.0128621 0.0128621 Diff = 5.21086e-08 or 0.000405132 %
Cyclic GGI pair (RU_PER2_40, RU_PER1_41)
Area: 0.000282615 0.00028262 Diff = -5.36601e-09 or 0.00189866 %
Flux: 0.00210837 0.00210715 Diff = 1.21723e-06 or 0.0577331 %
Cyclic GGI pair (RU_PER2_48, RU_PER1_49)
Area: 0.00188188 0.00188187 Diff = 9.59111e-09 or 0.000509656 %
Flux: 0.00671003 0.00670996 Diff = 7.05055e-08 or 0.00105075 %
Cyclic GGI pair (RU_PER2_52, RU_PER1_53)
Area: 0.000273776 0.000273778 Diff = -2.61869e-09 or 0.000956501 %
Flux: 0.00253421 0.00253325 Diff = 9.56178e-07 or 0.0377309 %
Cyclic GGI pair (RU_PER2_54, RU_PER1_55)
Area: 0.0357119 0.0357119 Diff = 1.63478e-08 or 4.57768e-05 %
Flux: 0.00324746 0.00322479 Diff = 2.26613e-05 or 0.697817 %
Cyclic GGI pair (GV_PER2_4, GV_PER1_5)
Area: 0.000768029 0.000767998 Diff = 3.08771e-08 or 0.00402031 %
Flux: 0.000212817 0.00021281 Diff = -7.02075e-09 or 0.00329896 %
Cyclic GGI pair (GV_PER2_12, GV_PER1_13)
Area: 0.000731156 0.000731155 Diff = 1.86157e-10 or 2.54606e-05 %
Flux: 7.46e-05 7.39707e-05 Diff = 6.29373e-07 or 0.843663 %
Cyclic GGI pair (GV_PER2_22, GV_PER1_23)
Area: 0.00409702 0.00409704 Diff = -2.41303e-08 or 0.000588969 %
Flux: 4.88098e-05 5.20643e-05 Diff = 3.25457e-06 or 6.25105 %
Time = 158

BiCGStab:  Solving for Ux, Initial residual = 0.00319198, Final residual = 6.75304e-09, No Iterations 1
BiCGStab:  Solving for Uy, Initial residual = 0.00559197, Final residual = 2.0179e-08, No Iterations 1
BiCGStab:  Solving for Uz, Initial residual = 0.0111151, Final residual = 1.89361e-08, No Iterations 1
BiCGStab:  Solving for p, Initial residual = 0.00439531, Final residual = 4.20597e-05, No Iterations 424
time step continuity errors : sum local = 0.0233547, global = -0.00184768, cumulative = 0.104819
ExecutionTime = 3069 s  ClockTime = 3095 s

Checking flux phi GGI balance.
Cyclic GGI pair (RU_PER2_31, RU_PER1_32)
Area: 0.00419516 0.00419517 Diff = -7.21973e-09 or 0.000172096 %
Flux: 0.0127264 0.0127265 Diff = -3.27529e-08 or 0.00025736 %
Cyclic GGI pair (RU_PER2_40, RU_PER1_41)
Area: 0.000282615 0.00028262 Diff = -5.36601e-09 or 0.00189866 %
Flux: 0.00211521 0.00211458 Diff = 6.34102e-07 or 0.0299782 %
Cyclic GGI pair (RU_PER2_48, RU_PER1_49)
Area: 0.00188188 0.00188187 Diff = 9.59111e-09 or 0.000509656 %
Flux: 0.00698973 0.00698969 Diff = 4.6548e-08 or 0.000665948 %
Cyclic GGI pair (RU_PER2_52, RU_PER1_53)
Area: 0.000273776 0.000273778 Diff = -2.61869e-09 or 0.000956501 %
Flux: 0.00251704 0.00251657 Diff = 4.70436e-07 or 0.0186901 %
Cyclic GGI pair (RU_PER2_54, RU_PER1_55)
Area: 0.0357119 0.0357119 Diff = 1.63478e-08 or 4.57768e-05 %
Flux: 0.00422807 0.0042229 Diff = 5.17106e-06 or 0.122303 %
Cyclic GGI pair (GV_PER2_4, GV_PER1_5)
Area: 0.000768029 0.000767998 Diff = 3.08771e-08 or 0.00402031 %
Flux: 7.99566e-05 7.99443e-05 Diff = -1.22629e-08 or 0.015337 %
Cyclic GGI pair (GV_PER2_12, GV_PER1_13)
Area: 0.000731156 0.000731155 Diff = 1.86157e-10 or 2.54606e-05 %
Flux: 0.000131652 0.000131379 Diff = 2.73525e-07 or 0.207763 %
Cyclic GGI pair (GV_PER2_22, GV_PER1_23)
Area: 0.00409702 0.00409704 Diff = -2.41303e-08 or 0.000588969 %
Flux: 0.000239929 0.000241775 Diff = 1.84622e-06 or 0.76361 %
Time = 159

BiCGStab:  Solving for Ux, Initial residual = 0.00208169, Final residual = 3.77051e-09, No Iterations 1
BiCGStab:  Solving for Uy, Initial residual = 0.00417301, Final residual = 1.4214e-08, No Iterations 1
BiCGStab:  Solving for Uz, Initial residual = 0.00666053, Final residual = 9.93652e-09, No Iterations 1
BiCGStab:  Solving for p, Initial residual = 0.00240458, Final residual = 2.04137e-05, No Iterations 413
time step continuity errors : sum local = 0.0120242, global = 0.00525349, cumulative = 0.110072
ExecutionTime = 3157.25 s  ClockTime = 3183 s

Checking flux phi GGI balance.
Cyclic GGI pair (RU_PER2_31, RU_PER1_32)
Area: 0.00419516 0.00419517 Diff = -7.21973e-09 or 0.000172096 %
Flux: 0.0127496 0.0127496 Diff = 1.44665e-08 or 0.000113466 %
Cyclic GGI pair (RU_PER2_40, RU_PER1_41)
Area: 0.000282615 0.00028262 Diff = -5.36601e-09 or 0.00189866 %
Flux: 0.00212391 0.00212307 Diff = 8.44639e-07 or 0.0397681 %
Cyclic GGI pair (RU_PER2_48, RU_PER1_49)
Area: 0.00188188 0.00188187 Diff = 9.59111e-09 or 0.000509656 %
Flux: 0.00688985 0.00688979 Diff = 5.94219e-08 or 0.000862456 %
Cyclic GGI pair (RU_PER2_52, RU_PER1_53)
Area: 0.000273776 0.000273778 Diff = -2.61869e-09 or 0.000956501 %
Flux: 0.00250937 0.00250875 Diff = 6.2748e-07 or 0.0250054 %
Cyclic GGI pair (RU_PER2_54, RU_PER1_55)
Area: 0.0357119 0.0357119 Diff = 1.63478e-08 or 4.57768e-05 %
Flux: 0.00367156 0.00365623 Diff = 1.53348e-05 or 0.417664 %
Cyclic GGI pair (GV_PER2_4, GV_PER1_5)
Area: 0.000768029 0.000767998 Diff = 3.08771e-08 or 0.00402031 %
Flux: 0.000437587 0.000437533 Diff = -5.40349e-08 or 0.0123484 %
Cyclic GGI pair (GV_PER2_12, GV_PER1_13)
Area: 0.000731156 0.000731155 Diff = 1.86157e-10 or 2.54606e-05 %
Flux: 6.92124e-05 7.00157e-05 Diff = 8.03274e-07 or 1.14728 %
Cyclic GGI pair (GV_PER2_22, GV_PER1_23)
Area: 0.00409702 0.00409704 Diff = -2.41303e-08 or 0.000588969 %
Flux: 0.000165434 0.000159137 Diff = 6.29721e-06 or 3.80648 %
Time = 160

BiCGStab:  Solving for Ux, Initial residual = 0.0020779, Final residual = 4.94615e-09, No Iterations 1
BiCGStab:  Solving for Uy, Initial residual = 0.00518341, Final residual = 2.08294e-08, No Iterations 1
BiCGStab:  Solving for Uz, Initial residual = 0.00698139, Final residual = 1.3822e-08, No Iterations 1
BiCGStab:  Solving for p, Initial residual = 0.00284496, Final residual = 2.84166e-05, No Iterations 462
time step continuity errors : sum local = 0.0177161, global = 0.00515314, cumulative = 0.115225
ExecutionTime = 3288.18 s  ClockTime = 3319 s

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