CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

OF8 - pimpleFoam: Increase in initial p residual at final iteration of each time step

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree3Likes
  • 1 Post By Tobermory
  • 1 Post By dlahaye
  • 1 Post By Tobermory

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 17, 2024, 13:27
Default OF8 - pimpleFoam: Increase in initial p residual at final iteration of each time step
  #1
Member
 
sirLentschi
Join Date: Nov 2010
Posts: 86
Rep Power: 15
lentschi is on a distinguished road
Hello,

I am currently running an LES WALE case in OF8 using pimpleFoam. An initial solution was adopted from a corresponding RANS simulation. I am encountering a significant increase in initial p residuals during the final iteration of each time step (from the beginning, up to the current time step = 407):

Code:
Courant Number mean: 0.008399714967 max: 0.7193162975
  132 Time = 5e-06
  133
  134 PIMPLE: Iteration 1
  135 smoothSolver:  Solving for Ux, Initial residual = 3.798020874e-06, Final residual = 2.178881283e-09, No Iterations  136 smoothSolver:  Solving for Uy, Initial residual = 1.23923313e-06, Final residual = 6.212075878e-10, No Iterations
  137 smoothSolver:  Solving for Uz, Initial residual = 3.326645723e-06, Final residual = 1.500835019e-09, No Iterations
  138 GAMGPCG:  Solving for p, Initial residual = 0.1039002852, Final residual = 7.321548563e-05, No Iterations 3
  139 GAMGPCG:  Solving for p, Initial residual = 0.007223483423, Final residual = 5.231179486e-06, No Iterations 4
  140 GAMGPCG:  Solving for p, Initial residual = 0.001099740598, Final residual = 4.479327689e-07, No Iterations 4
  141 time step continuity errors : sum local = 8.324539494e-12, global = 2.845274255e-13, cumulative = 2.845274255e-13
  142 GAMGPCG:  Solving for p, Initial residual = 0.03220724529, Final residual = 2.08032012e-05, No Iterations 3
  143 GAMGPCG:  Solving for p, Initial residual = 0.002289461202, Final residual = 1.813159765e-06, No Iterations 5
  144 GAMGPCG:  Solving for p, Initial residual = 0.0003657092185, Final residual = 6.333790375e-07, No Iterations 3
  145 time step continuity errors : sum local = 1.177320667e-11, global = -2.500815743e-13, cumulative = 3.444585116e-14
  
  ....
  
  182 PIMPLE: Iteration 5
  183 smoothSolver:  Solving for Ux, Initial residual = 3.571453512e-06, Final residual = 1.389921103e-09, No Iterations
  184 smoothSolver:  Solving for Uy, Initial residual = 5.873638525e-07, Final residual = 9.005931028e-09, No Iterations
  185 smoothSolver:  Solving for Uz, Initial residual = 1.298302045e-06, Final residual = 4.90217827e-10, No Iterations
  186 GAMGPCG:  Solving for p, Initial residual = 0.000810497471, Final residual = 3.461697627e-07, No Iterations 3
  187 GAMGPCG:  Solving for p, Initial residual = 4.458844283e-05, Final residual = 9.773047859e-08, No Iterations 3
  188 GAMGPCG:  Solving for p, Initial residual = 6.643134197e-06, Final residual = 7.799485967e-08, No Iterations 1
  189 time step continuity errors : sum local = 1.893199055e-12, global = -2.463948232e-15, cumulative = -2.505635775e-1
  190 GAMGPCG:  Solving for p, Initial residual = 0.0002424780533, Final residual = 1.0771658e-07, No Iterations 3
  191 GAMGPCG:  Solving for p, Initial residual = 1.31896789e-05, Final residual = 5.020704946e-08, No Iterations 2
  192 GAMGPCG:  Solving for p, Initial residual = 1.971721138e-06, Final residual = 2.429364249e-08, No Iterations 1
  193 time step continuity errors : sum local = 5.912169006e-13, global = -6.088530994e-15, cumulative = -3.114488874e-1
  194 PIMPLE: Converged
  195         Doing final iteration
  196 PIMPLE: Iteration 6
  197 smoothSolver:  Solving for Ux, Initial residual = 1.315012105e-06, Final residual = 1.081018863e-09, No Iterations
  198 smoothSolver:  Solving for Uy, Initial residual = 2.160959541e-07, Final residual = 4.776109417e-09, No Iterations
  199 smoothSolver:  Solving for Uz, Initial residual = 4.772566881e-07, Final residual = 9.535555309e-09, No Iterations
  200 GAMGPCG:  Solving for p, Initial residual = 0.3212578807, Final residual = 0.000273160544, No Iterations 3
  201 GAMGPCG:  Solving for p, Initial residual = 0.02012123337, Final residual = 1.017517052e-05, No Iterations 4
  202 GAMGPCG:  Solving for p, Initial residual = 0.00291566844, Final residual = 1.634454767e-06, No Iterations 4
  203 time step continuity errors : sum local = 3.007467842e-11, global = 1.636254419e-13, cumulative = 1.324805532e-13
  204 GAMGPCG:  Solving for p, Initial residual = 0.1235330451, Final residual = 0.0001013779859, No Iterations 3
  205 GAMGPCG:  Solving for p, Initial residual = 0.007228274664, Final residual = 3.421793683e-06, No Iterations 4
  206 GAMGPCG:  Solving for p, Initial residual = 0.001138691056, Final residual = 6.050579309e-07, No Iterations 4
  207 time step continuity errors : sum local = 1.114932749e-11, global = 2.85878474e-14, cumulative = 1.610684005e-13
  208 PIMPLE: Converged in 6 iterations
  209 ExecutionTime = 220.96 s  ClockTime = 221 s
Excerpt of fvSolution:

Code:
 20     p
 21     {
 22         solver          PCG;
 23         preconditioner
 24         {
 25             preconditioner  GAMG;
 26             tolerance       1e-7;
 27             relTol          0;
 28             nVcycles        2;
 29             smoother        GaussSeidel;
 30             nPreSweeps      0;
 31             nPostSweeps     2;
 32             nFinestSweeps   2;
 33             cacheAgglomeration on;
 34             nCellsInCoarsestLevel 10;
 35             agglomerator    faceAreaPair;
 36             mergeLevels     1;
 37         }
 38         tolerance       1e-7;
 39         relTol          0.001;
 40         minIter     1;
 41     }
 42
 43     pFinal
 44     {
 45         $p;
 46         tolerance       1e-06;
 47         relTol          0;
 48     }


 60 PIMPLE
 61 {
 62     nOuterCorrectors    50;
 63     momentumPredictor   true;
 64     nCorrectors         2;
 65     nNonOrthogonalCorrectors 2;
 66
 67     outerCorrectorResidualControl
 68     {
 69         "(U|(p).*)"
 70         {
 71                 tolerance  1e-3;
 72                 relTol     0;
 73         }
 74      }
 75 }


 78 relaxationFactors
 79 {
 80     fields
 81     {
 82           p                     0.7;
 83         "(p)Final"             1;
 84     }
 85     equations
 86     {
 87         U                         0.7;
 88         omega                  0.7;
 89         k                         0.7; 
 90
 91         "(U|k|omega)Final"      1;
 92     }
 93 }
Any hints? I am a bit at a loss.


Many thanks!


//Markus
lentschi is offline   Reply With Quote

Old   February 23, 2024, 14:07
Default
  #2
Member
 
sirLentschi
Join Date: Nov 2010
Posts: 86
Rep Power: 15
lentschi is on a distinguished road
No hints in this round?
lentschi is offline   Reply With Quote

Old   February 27, 2024, 05:46
Default
  #3
Senior Member
 
Join Date: Apr 2020
Location: UK
Posts: 670
Rep Power: 14
Tobermory will become famous soon enough
This usually occurs because the intermediate PIMPLE iterations are run with underrelaxation, to help smooth the convergence, whilst the final PIMPLE is run without relaxation to enforce continuity. Looking at your fvSolution file - this is exactly what you have got.

Post edit: see my post below - I meant "time accuracy" and not "continuity"; brain was on holiday!
dlahaye likes this.

Last edited by Tobermory; March 1, 2024 at 05:48.
Tobermory is offline   Reply With Quote

Old   March 1, 2024, 04:50
Default
  #4
Senior Member
 
Domenico Lahaye
Join Date: Dec 2013
Posts: 736
Blog Entries: 1
Rep Power: 17
dlahaye is on a distinguished road
@tobermory
Quote:
whilst the final PIMPLE is run without relaxation to enforce continuity.
Could you pls. elaborate on how you relate relaxation on p in the final PIMPLE with continuity. Do you encounter cases in which relaxation on p in the final PIMPLE is required to obtain convergence?

Many thanks. All the best.
Tobermory likes this.
dlahaye is offline   Reply With Quote

Old   March 1, 2024, 05:47
Default
  #5
Senior Member
 
Join Date: Apr 2020
Location: UK
Posts: 670
Rep Power: 14
Tobermory will become famous soon enough
Apologies Domenico - that was careless of me - relaxation of the p field has nothing to do with continuity (that's related to the p equation factor, which you'll note is always 1). What I meant to say was enforce "time accuracy" rather than "continuity". In other words, if you use a value of less than 1 for the p field relaxation factor, then you are artificially holding back the development of the pressure field. That may not be a problem, if you are searching for a steady state solution ... but will introduce some inaccuracy if you are trying for a true transient solution. I'll add a caution to my earlier post.
dlahaye likes this.
Tobermory is offline   Reply With Quote

Old   March 1, 2024, 14:28
Default
  #6
Member
 
sirLentschi
Join Date: Nov 2010
Posts: 86
Rep Power: 15
lentschi is on a distinguished road
Thank you very much for your clarification. I assumed that the relaxation has something to do with this issue but was not sure.
lentschi is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Help sought on axial compressor simulation jyotir OpenFOAM Running, Solving & CFD 0 November 17, 2021 10:49
Segmentation fault when using reactingFOAM for Fluids Tommy Floessner OpenFOAM Running, Solving & CFD 4 April 22, 2018 12:30
Unstabil Simulation with chtMultiRegionFoam mbay101 OpenFOAM Running, Solving & CFD 13 December 28, 2013 13:12
Micro Scale Pore, icoFoam gooya_kabir OpenFOAM Running, Solving & CFD 2 November 2, 2013 13:58
SLTS+rhoPisoFoam: what is rDeltaT??? nileshjrane OpenFOAM Running, Solving & CFD 4 February 25, 2013 04:13


All times are GMT -4. The time now is 17:42.