# Behaviour of the kOmegaSST in a steady-state case

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 June 23, 2015, 07:53 Behaviour of the kOmegaSST in a steady-state case #1 New Member   Max T Join Date: Feb 2015 Posts: 8 Rep Power: 11 Hi everybody, I have a problem with the convergence behavior of my simulation. It is a external and internal aerodynamic simulation of a reference car in a wind tunnel. It is steady state and uses the kOmegaSST turbulence model. The radiator is modelled by a porous media using the fvOptions. The rotating wheels are simulated by a rotating wall BC a the rotationally symmetric parts of the wheel (so mainly the tire) and a MRF Region for each wheel (mainly the rims). The movement of the floor is built like in a wind tunnel using a five belt system (so only moving wall BC). The final flow speed is 60m/s. I say "final flow Speed" because I started to simulate it with a speed of 5m/s. In this case all values except Omega startet so converge immediately. Omega's Initial redidual stayed constant for the first 400 timesteps and I reached my convergence criteria after 1900 timesteps. Now I startet a simulation with 20m/s and Omega shows the nearly the same behaviour with the small difference, that it still (after 1600 timesteps) didn't start to converge. And now I am worrying about the 60m/s simulation, because I haven't enough time to wait for thousands of timesteps untill it starts to converge. I think it is a numerical problem of the Omega solver. I am using a smoothSolver and I think it stucks at a local Optimum of the solution. I forgot to say, that i use the solver simpleFoam. Of course you need at least the fvSolution and the fvSchemes to help me and I will upload it at this evening. About the geometry I can only say, that it is a pretty complex geometry with at about 10 Million cells. Do you need some other files than the both fvS... files? Thank you very much for your help. Max

 June 23, 2015, 08:53 #2 Senior Member     Jan Join Date: Jul 2009 Location: Hamburg Posts: 133 Rep Power: 19 Hi Max, output of checkMesh would also be helpfull.

June 23, 2015, 14:25
#3
New Member

Max T
Join Date: Feb 2015
Posts: 8
Rep Power: 11
Hi,

here are the files. Firstly the output of checkMesh

Quote:
 Create time Create polyMesh for time = 0 Time = 0 Mesh stats points: 11342506 faces: 31037264 internal faces: 29782259 cells: 9887518 faces per cell: 6.15114 boundary patches: 33 point zones: 0 face zones: 0 cell zones: 5 Overall number of cells of each type: hexahedra: 8939041 prisms: 109247 wedges: 0 pyramids: 0 tet wedges: 1108 tetrahedra: 0 polyhedra: 838122 Breakdown of polyhedra by number of faces: faces number of cells 4 89521 5 54334 6 124726 7 123686 8 38936 9 302981 10 1060 11 164 12 69524 13 8 14 9 15 30550 17 5 18 2618 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 4272 4695 ok (non-closed singly connected) outlet 4272 4695 ok (non-closed singly connected) wall 19436 20851 ok (non-closed singly connected) floor 293442 296757 ok (non-closed singly connected) solid_air_duct 8562 9186 ok (non-closed singly connected) solid_base 15702 16763 ok (non-closed singly connected) solid_body 388662 419124 ok (non-closed singly connected) solid_engine 31916 33118 ok (non-closed singly connected) solid_exhaust_pipe 11530 13089 ok (non-closed singly connected) solid_fan 4597 4928 ok (non-closed singly connected) solid_gear_box 7803 8575 ok (non-closed singly connected) solid_grill_lower 15162 15617 ok (non-closed singly connected) solid_grill_upper 32363 33085 ok (non-closed singly connected) solid_mirrors 3426 4020 ok (non-closed singly connected) solid_radiator_frame 9742 10421 ok (non-closed singly connected) solid_shroud 8367 8903 ok (non-closed singly connected) solid_suspension 17318 19092 ok (non-closed singly connected) solid_UBV 46860 48119 ok (non-closed singly connected) solid_wheel_housing 19864 23272 ok (non-closed singly connected) solid_wheels_front_wheels_front_rim_left 15616 18302 ok (non-closed singly connected) solid_wheels_front_wheels_front_tire_right 52578 60941 ok (non-closed singly connected) solid_wheels_front_wheels_front_tire_left 52581 60943 ok (non-closed singly connected) solid_wheels_front_wheels_front_rim_right 15616 18302 ok (non-closed singly connected) solid_wheels_rear_wheels_rear_tire_right 53636 61796 ok (non-closed singly connected) solid_wheels_rear_wheels_rear_rim_right 14586 17238 ok (non-closed singly connected) solid_wheels_rear_wheels_rear_tire_left 53638 61798 ok (non-closed singly connected) solid_wheels_rear_wheels_rear_rim_left 14584 17236 ok (non-closed singly connected) solid_wheel_suspension 2698 3028 ok (non-closed singly connected) center_belt 30760 31288 ok (non-closed singly connected) wru_front_left 1325 1598 ok (non-closed singly connected) wru_front_right 1325 1598 ok (non-closed singly connected) wru_rear_left 1383 1651 ok (non-closed singly connected) wru_rear_right 1383 1651 ok (non-closed singly connected) Checking geometry... Overall domain bounding box (-11.008 -6.144 -0.0783773) (11.008 6.144 7.4241) Mesh (non-empty, non-wedge) directions (1 1 1) Mesh (non-empty) directions (1 1 1) Boundary openness (6.57295e-15 -6.11382e-17 3.2418e-15) OK. Max cell openness = 4.39346e-16 OK. Max aspect ratio = 34.0365 OK. Minimum face area = 3.03918e-08. Maximum face area = 0.0664327. Face area magnitudes OK. Min volume = 2.76961e-11. Max volume = 0.0169934. Total volume = 2029.55. Cell volumes OK. Mesh non-orthogonality Max: 74.9905 average: 10.8433 *Number of severely non-orthogonal (> 70 degrees) faces: 2415. Non-orthogonality check OK. <
Next the fvSolution

Quote:
 /*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 2.3.1 | | \\ / A nd | Web: www.OpenFOAM.org | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; object fvSolution; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // solvers { p { solver GAMG; tolerance 1e-8; relTol 0.05; smoother GaussSeidel; cacheAgglomeration true; agglomerator faceAreaPair; nCellsInCoarsestLevel 20; mergeLevels 1; } U { solver smoothSolver; smoother GaussSeidel; tolerance 1e-7; relTol 0.1; nSweeps 2; } k { solver smoothSolver; smoother GaussSeidel; tolerance 1e-7; relTol 0.1; nSweeps 2; } omega { solver smoothSolver; smoother GaussSeidel; tolerance 1e-7; relTol 0.1; nSweeps 2; } } SIMPLE { nNonOrthogonalCorrectors 0; pRefCell 0; pRefValue 0; residualControl { p 5e-3; U 1e-3; "(k|omega)" 1e-4; } } potentialFlow { nNonOrthogonalCorrectors 10; } relaxationFactors { fields { p 0.3; } equations { U 0.5; k 0.5; omega 0.5; } } cache { grad(U); } // ************************************************** *********************** //
And finally the fvSchemes:

Quote:
 /*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 2.3.1 | | \\ / A nd | Web: www.OpenFOAM.org | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; object fvSchemes; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // ddtSchemes { default steadyState; } gradSchemes { default Gauss linear; } divSchemes { default none; div(phi,U) bounded Gauss limitedLinear 1; div(phi,k) bounded Gauss limitedLinear 1; div(phi,omega) bounded Gauss limitedLinear 1; div((nuEff*dev(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } fluxRequired { default no; p; } // ************************************************** *********************** //
I hope somebody has an idea. Thank you.
Max

 June 24, 2015, 03:42 #4 New Member   Max T Join Date: Feb 2015 Posts: 8 Rep Power: 11 Hi, additionally I started a transient case this morning using the pimpleFoam solver and kEpsilon. Maybe the local turbulence is too high to solve this case as global steady-state. Max

 June 25, 2015, 09:51 #5 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26 Hey Max, as I understand your first post, it is the outer (SIMPLE) iterations that don't converge for omega. Then, you write about the omega solver itself, but this is related to the inner / linear iterations. Why do you expect an error in the inner solver, when the outer iterations are stuck? __________________ The skeleton ran out of shampoo in the shower.

 June 25, 2015, 10:04 #6 Senior Member     Jan Join Date: Jul 2009 Location: Hamburg Posts: 133 Rep Power: 19 Hi Max, some ideas: the more complex the flow (mesh) the more iterations you need to have a converged solution. More than e.g. 2000 is quite normal in my experience. LimitedLinear for turbulence equations is optimistic, try linearUpwind (see motorBike tutorial) or even upwind, of course only for the turbulence equations. Also try limited schemes for laplacian and snGrad schemes, e.g 0.5 Best regards, Jan RodriguezFatz likes this.

 June 29, 2015, 08:02 #7 New Member   Max T Join Date: Feb 2015 Posts: 8 Rep Power: 11 Hi, Thanks for the good ideas. I startet a simulation using the recommended changes at the fvSolution last Friday. I also changed the speed to an inlet velocity of 60m/s. But the simulation stopped after 6 timesteps. I will upload the log-file this evening. Max

 June 29, 2015, 08:55 #8 Super Moderator     Tobias Holzmann Join Date: Oct 2010 Location: Tussenhausen Posts: 2,702 Blog Entries: 6 Rep Power: 51 Hello Max, 1900 Iterations are not really a lot of iteration. In my combustion solver I have to run something like 30.000 Iterations till I reach a steady state situation. This always depend on the initial values of your simulation. You can use the previous lower velocity solution and start with that but with a higher velocity inlet. That helps a lot in convergence and speed up the simulation. Thus, you can use renumberMesh to speed up your case too. What about your relaxation of omega? I hope you did not forget to set this because in the standard tutorials there is no omega included (as far as I know). If your problem is complex, maybe the mesh should be improved, or your BC are not really a good choice. Relaxation is a topic too and of course all the stuff what is mentioned above. Good luck. arashgmn likes this. __________________ Keep foaming, Tobias Holzmann

 June 29, 2015, 09:42 #9 New Member   Max T Join Date: Feb 2015 Posts: 8 Rep Power: 11 Hi Tobi, I have set a relaxation for omega from the start. As rodriguezFatz said, it's a problem with the simple algorithm. Using pimplefoam there is no problem at all, but I'd really like to use simplefoam. My BC I checked several times, but there could be a mesh problem. Seading my case with a one with a lower velocity I was also thinking about, maybe that's the best I could do. Except from waiting... I will try your ideas this evening. Maybe I'm wrong, but can't I also use the slower simple case for a fast pimple case? Thank you very much. Max

 June 29, 2015, 09:44 #10 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26 You need to post the log file for better assistance. Edit: I am not quite sure if you understood what I meant in my post. Tobi likes this. __________________ The skeleton ran out of shampoo in the shower.

 June 30, 2015, 03:45 #11 Senior Member   Francesco Del Citto Join Date: Mar 2009 Location: Zürich Area, Switzerland Posts: 237 Rep Power: 17 Hi Max, Your mesh is not great, but you should be able to obtain a solution. What are your initial condition? Have you tried to initialise the flow with potentialFoam? This usually helps a lot. Cheers, Francesco

July 2, 2015, 02:49
#12
New Member

Max T
Join Date: Feb 2015
Posts: 8
Rep Power: 11
Hi,
I think the main BC's should be correct.

Inlet
U fixedValue (60,0,0)
omega fixedValue
nut calculated

Outlet
p fixedValue 0
omega inletOutlet
nut calculated

Walls
U fixedValue (0,0,0)
omega omegaWallFunction \$internalField
k kqRWallFunction \$internalField
nut nutkWallFunction \$internalField

5-belt-system
U movingWallVelocity (60,0,0)
omega omegaWallFunction \$internalField
k kqRWallFunction \$internalField
nut nutkWallFunction \$internalField

car
U fixedValue (0,0,0)
omega omegaWallFunction \$internalField
k kqRWallFunction \$internalField
nut nutkWallFunction \$internalField

car_tires
U rotatingWallVelocity
omega omegaWallFunction \$internalField
k kqRWallFunction \$internalField
nut nutkWallFunction \$internalField
Direction and rotational speed is checked

car_rims
Here I created cellZones with topoSet and defined MRF-Zones with the fvOptions. Same values and axes as the tires.

So I think the BCs of the Inlet and the outlet could be improved, but I thought, that it should be already runable with these BCs. I was using potentialFoam every case I was running, but this time I tried the argument -initialiseUBCs. But the simulation stopped after 10 timesteps. Here the log-file:

Quote:
 /*---------------------------------------------------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 2.4.0 | | \\ / A nd | Web: www.OpenFOAM.org | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ Build : 2.4.0-f0842aea0e77 Exec : simpleFoam Date : Jul 01 2015 Time : 21:46:21 PID : 4545 Case : /opt/run/aeroSteady_MT01072015 nProcs : 1 sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE). fileModificationChecking : Monitoring run-time modified files using timeStampMaster allowSystemOperations : Allowing user-supplied system call operations // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // Create time Create mesh for time = 0 Reading field p Reading field U Reading/calculating face flux field phi Selecting incompressible transport model Newtonian Selecting RAS turbulence model kOmegaSST kOmegaSSTCoeffs { alphaK1 0.85; alphaK2 1; alphaOmega1 0.5; alphaOmega2 0.856; gamma1 0.555556; gamma2 0.44; beta1 0.075; beta2 0.0828; betaStar 0.09; a1 0.31; b1 1; c1 10; F3 false; } Creating finite volume options from "system/fvOptions" Selecting finite volume options model type MRFSource Source: MRF1 - applying source for all time - selecting cells using cellZone mrf_volume_front_left - selected 48869 cell(s) with volume 8.66941e-05 Selecting finite volume options model type MRFSource Source: MRF2 - applying source for all time - selecting cells using cellZone mrf_volume_front_right - selected 48845 cell(s) with volume 8.66575e-05 Selecting finite volume options model type MRFSource Source: MRF3 - applying source for all time - selecting cells using cellZone mrf_volume_rear_left - selected 49567 cell(s) with volume 8.95837e-05 Selecting finite volume options model type MRFSource Source: MRF4 - applying source for all time - selecting cells using cellZone mrf_volume_rear_right - selected 49591 cell(s) with volume 8.9623e-05 SIMPLE: convergence criteria field p tolerance 0.001 field U tolerance 0.0001 field "(k|epsilon|omega)" tolerance 1e-05 Starting time loop Reading surface description: yNormal forceCoeffs forceCoeffs1: Not including porosity effects Time = 1 smoothSolver: Solving for Ux, Initial residual = 0.00214738, Final residual = 0.000145893, No Iterations 3 smoothSolver: Solving for Uy, Initial residual = 0.106149, Final residual = 0.00682049, No Iterations 3 smoothSolver: Solving for Uz, Initial residual = 0.0700754, Final residual = 0.00561898, No Iterations 2 GAMG: Solving for p, Initial residual = 1, Final residual = 0.00674501, No Iterations 13 time step continuity errors : sum local = 0.000145054, global = -1.53116e-05, cumulative = -1.53116e-05 smoothSolver: Solving for omega, Initial residual = 0.00108313, Final residual = 9.85236e-05, No Iterations 3 bounding omega, min: -10209.9 max: 1.0531e+06 average: 1491.17 smoothSolver: Solving for k, Initial residual = 1, Final residual = 0.0465201, No Iterations 4 ExecutionTime = 603.98 s ClockTime = 1463 s forceCoeffs forceCoeffs1 output: Cm = 0.145217 Cd = 2.20251 Cl = -1.59432 Cl(f) = -0.651942 Cl(r) = -0.942376 Time = 2 smoothSolver: Solving for Ux, Initial residual = 0.0184341, Final residual = 0.000558471, No Iterations 2 smoothSolver: Solving for Uy, Initial residual = 0.427426, Final residual = 0.00744874, No Iterations 2 smoothSolver: Solving for Uz, Initial residual = 0.449388, Final residual = 0.00828222, No Iterations 2 GAMG: Solving for p, Initial residual = 0.0575339, Final residual = 0.000377759, No Iterations 12 time step continuity errors : sum local = 0.000104903, global = -3.08856e-06, cumulative = -1.84001e-05 smoothSolver: Solving for omega, Initial residual = 0.00307868, Final residual = 0.000220552, No Iterations 4 bounding omega, min: -7.20885 max: 6.81923e+14 average: 1.45861e+09 smoothSolver: Solving for k, Initial residual = 0.00500152, Final residual = 0.000275102, No Iterations 1 ExecutionTime = 971.26 s ClockTime = 2436 s forceCoeffs forceCoeffs1 output: Cm = 0.19666 Cd = 3.83183 Cl = -2.94906 Cl(f) = -1.27787 Cl(r) = -1.67119 Time = 3 smoothSolver: Solving for Ux, Initial residual = 0.814136, Final residual = 0.0486659, No Iterations 4 smoothSolver: Solving for Uy, Initial residual = 0.99902, Final residual = 0.0630418, No Iterations 4 smoothSolver: Solving for Uz, Initial residual = 0.995703, Final residual = 0.062805, No Iterations 4 GAMG: Solving for p, Initial residual = 0.630178, Final residual = 0.00310921, No Iterations 4 time step continuity errors : sum local = 8.92089, global = -0.00105117, cumulative = -0.00106957 smoothSolver: Solving for omega, Initial residual = 0.538466, Final residual = 3.63298e-09, No Iterations 1 bounding omega, min: -4.61813e+06 max: 2.04577e+14 average: 4.3806e+08 smoothSolver: Solving for k, Initial residual = 0.110096, Final residual = 0.0045401, No Iterations 2 ExecutionTime = 1320.53 s ClockTime = 3378 s forceCoeffs forceCoeffs1 output: Cm = 476.833 Cd = 5543.13 Cl = 14137.7 Cl(f) = 7545.7 Cl(r) = 6592.03 Time = 4 smoothSolver: Solving for Ux, Initial residual = 0.562065, Final residual = 0.0233287, No Iterations 3 smoothSolver: Solving for Uy, Initial residual = 0.573858, Final residual = 0.0224044, No Iterations 3 smoothSolver: Solving for Uz, Initial residual = 0.594993, Final residual = 0.025018, No Iterations 3 GAMG: Solving for p, Initial residual = 0.930801, Final residual = 0.00870941, No Iterations 114 time step continuity errors : sum local = 7.8706, global = -1.22715, cumulative = -1.22822 smoothSolver: Solving for omega, Initial residual = 0.538455, Final residual = 1.93868e-07, No Iterations 1 bounding omega, min: -3064.16 max: 6.13731e+13 average: 1.31573e+08 smoothSolver: Solving for k, Initial residual = 0.0347727, Final residual = 0.00289815, No Iterations 3 ExecutionTime = 1933.35 s ClockTime = 4591 s forceCoeffs forceCoeffs1 output: Cm = 3.6495e+09 Cd = -1.37355e+08 Cl = -8.4765e+10 Cl(f) = -3.8733e+10 Cl(r) = -4.6032e+10 Time = 5 smoothSolver: Solving for Ux, Initial residual = 0.514354, Final residual = 0.0295775, No Iterations 3 smoothSolver: Solving for Uy, Initial residual = 0.510212, Final residual = 0.0371913, No Iterations 3 smoothSolver: Solving for Uz, Initial residual = 0.513935, Final residual = 0.0429204, No Iterations 3 GAMG: Solving for p, Initial residual = 1.01566e-06, Final residual = 9.46779e-08, No Iterations 3 time step continuity errors : sum local = 67.4263, global = 0.313691, cumulative = -0.91453 smoothSolver: Solving for omega, Initial residual = 0.538434, Final residual = 3.18436e-07, No Iterations 1 bounding omega, min: -7308.98 max: 1.84119e+13 average: 3.95139e+07 smoothSolver: Solving for k, Initial residual = 0.0127437, Final residual = 0.00109737, No Iterations 3 ExecutionTime = 2281.48 s ClockTime = 5544 s forceCoeffs forceCoeffs1 output: Cm = -1.06918e+09 Cd = -2.15708e+10 Cl = -1.26863e+11 Cl(f) = -6.45006e+10 Cl(r) = -6.23623e+10 Time = 6 smoothSolver: Solving for Ux, Initial residual = 0.435054, Final residual = 0.0303544, No Iterations 5 smoothSolver: Solving for Uy, Initial residual = 0.492075, Final residual = 0.0468131, No Iterations 3 smoothSolver: Solving for Uz, Initial residual = 0.442942, Final residual = 0.0302857, No Iterations 4 GAMG: Solving for p, Initial residual = 2.1378e-05, Final residual = 1.6657e-07, No Iterations 9 time step continuity errors : sum local = 331.245, global = -11.2961, cumulative = -12.2106 smoothSolver: Solving for omega, Initial residual = 0.532998, Final residual = 0.00145076, No Iterations 1 bounding omega, min: -0.000784596 max: 5.52405e+12 average: 1.20666e+07 smoothSolver: Solving for k, Initial residual = 0.0193182, Final residual = 0.00174137, No Iterations 3 ExecutionTime = 2628.35 s ClockTime = 6465 s forceCoeffs forceCoeffs1 output: Cm = 8.82291e+09 Cd = -4.34566e+09 Cl = -3.23404e+10 Cl(f) = -7.34731e+09 Cl(r) = -2.49931e+10 Time = 7 smoothSolver: Solving for Ux, Initial residual = 0.483845, Final residual = 0.0336438, No Iterations 3 smoothSolver: Solving for Uy, Initial residual = 0.505909, Final residual = 0.0346509, No Iterations 3 smoothSolver: Solving for Uz, Initial residual = 0.488301, Final residual = 0.0314531, No Iterations 3 GAMG: Solving for p, Initial residual = 9.0698e-05, Final residual = 8.43222e-07, No Iterations 167 time step continuity errors : sum local = 1032.83, global = -694.237, cumulative = -706.448 smoothSolver: Solving for omega, Initial residual = 0.389922, Final residual = 0.0381758, No Iterations 1 smoothSolver: Solving for k, Initial residual = 0.00339684, Final residual = 0.000179562, No Iterations 4 ExecutionTime = 3362.12 s ClockTime = 7813 s forceCoeffs forceCoeffs1 output: Cm = 3.96893e+14 Cd = -1.30111e+13 Cl = 3.61902e+15 Cl(f) = 2.20641e+15 Cl(r) = 1.41262e+15 Time = 8 smoothSolver: Solving for Ux, Initial residual = 0.510707, Final residual = 0.0388976, No Iterations 3 smoothSolver: Solving for Uy, Initial residual = 0.391124, Final residual = 0.0343672, No Iterations 3 smoothSolver: Solving for Uz, Initial residual = 0.386794, Final residual = 0.0324804, No Iterations 3 GAMG: Solving for p, Initial residual = 1.42187e-07, Final residual = 4.49518e-08, No Iterations 1 time step continuity errors : sum local = 48617.2, global = -193.335, cumulative = -899.783 smoothSolver: Solving for omega, Initial residual = 0.33843, Final residual = 0.0147085, No Iterations 3 smoothSolver: Solving for k, Initial residual = 0.0168934, Final residual = 0.00164581, No Iterations 3 ExecutionTime = 3694.08 s ClockTime = 8731 s forceCoeffs forceCoeffs1 output: Cm = 1.50654e+16 Cd = -2.56672e+17 Cl = -8.02582e+16 Cl(f) = -2.50636e+16 Cl(r) = -5.51945e+16 Time = 9 smoothSolver: Solving for Ux, Initial residual = 0.434079, Final residual = 0.0423767, No Iterations 11 smoothSolver: Solving for Uy, Initial residual = 0.396288, Final residual = 0.0289426, No Iterations 12 smoothSolver: Solving for Uz, Initial residual = 0.405692, Final residual = 0.025783, No Iterations 12 GAMG: Solving for p, Initial residual = 0.000538875, Final residual = 3.92192e-05, No Iterations 1000 time step continuity errors : sum local = 2.52333e+09, global = 2.1412e+09, cumulative = 2.1412e+09 smoothSolver: Solving for omega, Initial residual = 0.598808, Final residual = 0.0223923, No Iterations 3 smoothSolver: Solving for k, Initial residual = 0.0114434, Final residual = 0.000690612, No Iterations 12 ExecutionTime = 6436.91 s ClockTime = 12074 s forceCoeffs forceCoeffs1 output: Cm = 5.12029e+17 Cd = 8.74243e+19 Cl = -5.85838e+19 Cl(f) = -2.87799e+19 Cl(r) = -2.98039e+19 Time = 10 smoothSolver: Solving for Ux, Initial residual = 0.479676, Final residual = 0.0391509, No Iterations 3 smoothSolver: Solving for Uy, Initial residual = 0.547761, Final residual = 0.0419616, No Iterations 3 smoothSolver: Solving for Uz, Initial residual = 0.393054, Final residual = 0.0363214, No Iterations 3 GAMG: Solving for p, Initial residual = 0.998489, Final residual = 0.0892845, No Iterations 1000 time step continuity errors : sum local = 1.14593e+16, global = -1.39648e+14, cumulative = -1.39646e+14 smoothSolver: Solving for omega, Initial residual = 0.449707, Final residual = 0.0305966, No Iterations 14 smoothSolver: Solving for k, Initial residual = 0.359738, Final residual = 0.0238417, No Iterations 4 ExecutionTime = 9157.95 s ClockTime = 15375 s forceCoeffs forceCoeffs1 output: Cm = 4.41418e+26 Cd = 1.36257e+28 Cl = -8.57928e+27 Cl(f) = -3.84822e+27 Cl(r) = -4.73106e+27 Time = 11 smoothSolver: Solving for Ux, Initial residual = 0.696349, Final residual = 0.591836, No Iterations 1000 smoothSolver: Solving for Uy, Initial residual = 0.6991, Final residual = 0.343637, No Iterations 1000 smoothSolver: Solving for Uz, Initial residual = 0.438022, Final residual = 124.356, No Iterations 1000 #0 Foam::error:rintStack(Foam::Ostream&) at ??:? #1 Foam::sigFpe::sigHandler(int) at ??:? #2 ? in "/lib/x86_64-linux-gnu/libc.so.6" #3 Foam::GAMGSolver::scale(Foam::Field&, Foam::Field&, Foam::lduMatrix const&, Foam::FieldField const&, Foam::UPtrList const&, Foam::Field const&, unsigned char) const at ??:? #4 Foam::GAMGSolver::Vcycle(Foam::PtrList const&, Foam::Field&, Foam::Field const&, Foam::Field&, Foam::Field&, Foam::Field&, Foam::Field&, Foam::Field&, Foam::PtrList >&, Foam::PtrList >&, unsigned char) const at ??:? #5 Foam::GAMGSolver::solve(Foam::Field&, Foam::Field const&, unsigned char) const at ??:? #6 Foam::fvMatrix::solveSegregated(Foam::dict ionary const&) at ??:? #7 Foam::fvMatrix::solve(Foam::dictionary const&) at ??:? #8 ? at ??:? #9 ? at ??:? #10 __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6" #11 ? at ??:?
I added the error message at the end. In the past I was only using pretty easy CFD-Software like PowerFLOW or StarCCM and I'm still at the beginning of learning openFoam, but I hope this case will be runable anytime. Thanks for your help,

Max

 July 2, 2015, 03:04 #13 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26 Well I would run it with Code: ```laplacianSchemes { default Gauss linear uncorrected; } divSchemes { default bounded Gauss upwind; div((nuEff*dev(T(grad(U))))) Gauss linear; }``` which is much more stable. And then post the log file again __________________ The skeleton ran out of shampoo in the shower.

July 2, 2015, 07:24
#14
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Max T
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Hi,

with these ones it runs, thanks a lot! Done 22 timesteps till yet, because my regular computer isn't available. See residuals, I think convergence behaviour is ok. Thanks a lot, I will post again as the run has completed.

Max

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 July 2, 2015, 07:30 #15 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26 You can usually get rid of these "bounding Omega" errors by switching off the laplacian correction (-> "Gauss linear uncorrected"). You could also do that just for the omega laplacian. Also of course divScheme upwind is much more stable than your previous scheme. __________________ The skeleton ran out of shampoo in the shower.

July 2, 2015, 07:38
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Tobias Holzmann
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Quote:
 Originally Posted by RodriguezFatz Also of course divScheme upwind is much more stable than your previous scheme.
But your solution gets very diffusive (just as a hint).
Maybe you can switch to a high order scheme after a few timesteps, or even after the solution is converged to improve your gradients.
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Keep foaming,
Tobias Holzmann

October 30, 2018, 14:10
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Quote:
 Originally Posted by Max1234 Hi, additionally I started a transient case this morning using the pimpleFoam solver and kEpsilon. Maybe the local turbulence is too high to solve this case as global steady-state. Max
I know this is an old post. I have tried to obtain the steady-state solution with K-Omega SST with both Fluent and OpenFOAM. It is always problematic. I can only get the convergence with low order scheme. If I switch the model to 2nd order after it converged with the low order, it will still blow up. If it does not blow up, the residual look ugly and rarely the model is useful. I have been told by people in NASA that they always run SST in unsteady fashion.

Thanks,
Rdf

 October 31, 2018, 02:15 #18 Super Moderator     Tobias Holzmann Join Date: Oct 2010 Location: Tussenhausen Posts: 2,702 Blog Entries: 6 Rep Power: 51 Hi Randolf, is there any question or was it just a comment to the discussion above? __________________ Keep foaming, Tobias Holzmann

October 31, 2018, 09:03
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Quote:
 Originally Posted by Tobi Hi Randolf, is there any question or was it just a comment to the discussion above?
Hi Tobi,

I just want to share some experience. And I think the steady-state solution for high numerical Reynolds number simulation (rhoVL/(miu+miu_t)) with RANS, the numerical solution itself may be just a trade-off between order accuracy (diffusion and dispersion error, etc) and absolute convergence (stability and residual). There is no well-grounded practice guidance. The actual usefulness of the solution is religious. Someone please correct me if I understand this problem wrong (I think I am absolutely wrong on this, but I can not interpret my experience in another possible way...).

"1900 Iterations are not really a lot of iteration. In my combustion solver I have to run something like 30.000 Iterations till I reach a steady state situation."

Can you share some details of your simulation? the complexity of your geometry, M, Re, model,etc. And also how satisfied you are with your steady-state solution?

Thanks,
Rdf

 Tags convergence problem, k omega sst, simplefoam