Difference between revisions of "OpenFOAM guide/The PISO algorithm in OpenFOAM"

Revision as of 22:47, 12 March 2007

1 The PISO algorithm

TODO: Add a description of the algorithm here.

2 Implementation of the PISO algorithm in OpenFOAM

The PISO algorithm is implemented in OpenFOAM as follows (Details can be found in the icoFoam standard solver provided with OpenFOAM):

• Define the equation for U

 
 fvVectorMatrix UEqn
 (
   	fvm::ddt(U)
      + fvm::div(phi, U)
      - fvm::laplacian(nu, U)
 );

• Solve the momentum predictor

 
 solve (UEqn == -fvc::grad(p));

• Calculate the coefficient and calculate U

 
 volScalarField AU = UEqn().A();
 U = UEqn().H()/AU;

• Calculate the flux

 
 phi = (fvc::interpolate(U) & mesh.Sf()) 
       + fvc::ddtPhiCorr(1/AU, U, phi);
 adjustPhi(phi, U, p);

• Define and solve the pressure equation and repeat for the prescribed number of non-orthogonal corrector steps

 
 fvScalarMatrix pEqn
 (
    fvm::laplacian(1.0/AU, p) == fvc::div(phi)
 );
 pEqn.setReference(pRefCell, pRefValue);
 pEqn.solve();

• Correct the flux

 
 phi -= pEqn.flux();

• Calculate continuity errors

 
# include "continuityErrs.H"

• Perform the momentum corrector step

 
 U -= fvc::grad(p)/AU;
 U.correctBoundaryConditions();

• Repeat from the calculation of for the prescribed number of PISO corrector steps.