- **OpenFOAM**
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- - **How does openFoam calculate residuals?**
(*https://www.cfd-online.com/Forums/openfoam/73183-how-does-openfoam-calculate-residuals.html*)

How does openFoam calculate residuals?I have solved a case with the density based solver rhoPisoFoam. When I checked the residuals for convergence, I noticed that the residuals for Rho were zero in every time step. Does anyone know how it can be? Does any body know how does OpenFoam calculate the residuals in every timestep?
Since the Piso loop in solver solves the rho, I thought this can be the result. But rho is being solved several times in piso loop, so it is changing, and this can be the method for calculation of residuals? |

Quote:
I know how the linear solver residual is calculated. But how the SIMPLE residual is calculated? |

I'm interested in this topic and will try to contribue what I can.
The correction of rho is outside of the PISO loop. https://github.com/OpenCFD/OpenFOAM-.../rhoPisoFoam.C See the: Code:
`#include "rhoEqn.H"` Code:
`solve(fvm::ddt(rho) + fvc::div(phi));` Houthuys, if you could exlpain the linear solver residual, I'd be grateful. I found this on the OF+ site. Do you understand this? I guess and but I still don't understand the logic behind the calculation of . |

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