# solving pressure equation

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 May 18, 2010, 18:07 solving pressure equation #1 Member   Pascal Join Date: Jun 2009 Location: Montreal Posts: 65 Rep Power: 10 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

 May 19, 2010, 02:30 #2 Senior Member   Gijsbert Wierink Join Date: Mar 2009 Posts: 383 Rep Power: 11 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 ... __________________ Regards, Gijs

 May 19, 2010, 03:33 #3 Senior Member     Anton Kidess Join Date: May 2009 Location: Germany Posts: 1,261 Rep Power: 23 While your at it, you should do some reading on how PISO works in Ferziger/Peric or the original paper by Issa and Olivera...

 May 19, 2010, 18:48 #4 Member   Pascal Join Date: Jun 2009 Location: Montreal Posts: 65 Rep Power: 10 Thank you for all the information Pascal

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