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 Pascal_doran May 18, 2010 18:07

solving pressure equation

Hi all,

I am simulating wake vortices in ground effect and I'm using the icoFOAM application. I would like to know why it solve twice for p at each time step. I have no error message or warning just the following output when I'm solving.

Code:

```Courant Number mean: 0.0258412 max: 0.99935 deltaT = 0.000909091 Time = 0.000909091 DILUPBiCG:  Solving for Ux, Initial residual = 0.00117738, Final residual = 8.40907e-08, No Iterations 4 DILUPBiCG:  Solving for Uy, Initial residual = 0.00100752, Final residual = 6.02822e-07, No Iterations 3 DICPCG:  Solving for p, Initial residual = 0.360239, Final residual = 9.95302e-07, No Iterations 982 time step continuity errors : sum local = 1.82785e-10, global = 4.3745e-21, cumulative = 4.3745e-21 DICPCG:  Solving for p, Initial residual = 0.00983221, Final residual = 9.57613e-07, No Iterations 872 time step continuity errors : sum local = 2.375e-10, global = -6.8944e-20, cumulative = -6.45695e-20 ExecutionTime = 40.92 s  ClockTime = 42 s```
This increase a lot the duration of the simulation. Can anybody explain to me why it is like that.

Thank you,

Pascal

 gwierink May 19, 2010 02:30

Hi Pascal,

"Solving for p ..." shows up twice because in icoFoam's standard setting the number of pressure corrections in the PISO loop is set to two. If you wish, you can change this at the bottom of the system/fvSolution file where it reads

Code:

```PISO {     nCorrectors    2;     nNonOrthogonalCorrectors 0;     pRefCell        0;     pRefValue      0; }```
But I would leave it at 2, or even increase it for less orthogonal meshes ...

 akidess May 19, 2010 03:33

While your at it, you should do some reading on how PISO works in Ferziger/Peric or the original paper by Issa and Olivera...

 Pascal_doran May 19, 2010 18:48

Thank you for all the information

Pascal

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