- **OpenFOAM**
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- - **Momentum predictor**
(*https://www.cfd-online.com/Forums/openfoam/90500-momentum-predictor.html*)

Momentum predictorHi all,
i have 2 questions about the solution procedure in interFoam. The predicted fluxes are bulid in pEqn.H, if i'm not wrong: Code:
`volScalarField rAU(1.0/UEqn.A());` Code:
`00019 if (pimple.momentumPredictor())` fvc::ddtPhiCorr(rAU, rho, U, phi) in the phiU calculation? thanks a lot in advance andrea |

Andrea, predicted velocity is taken into account in H method (check Hrv Thesis). ddtPhiCorr is intended to apply a correction to Rhie-Chow interpolation due temporal scheme.
Regards. |

Hi Santiago and thanks to your reply.
If i'm not wrong, H is a function of U (it takes into into account the velocities of the neighboring cells). So, if the momentum predictor is turned off, which is the velocity used to bulid up H? Or in another way, are these lines (below) used to calculate a velocity or are used only to do an update of the coefficients of the matrices A and H? 00019 if (pimple.momentumPredictor()) 00020 { 00021 solve 00022 ( 00023 UEqn 00024 == 00025 fvc::reconstruct 00026 ( 00027 ( 00028 fvc::interpolate(interface.sigmaK())*fvc::snGrad(alpha1) 00029 - ghf*fvc::snGrad(rho) 00030 - fvc::snGrad(p_rgh) 00031 ) * mesh.magSf() 00032 ) 00033 ); 00034 } |

Andrea, if momentum predictor is turned off, U from previous time-step is used, if it is on once the solve method is executed U is refreshed and then used in H method.
Regards. |

Ok, now it's totally clear!!
many thanks andrea |

Hi Santiago,
i'm still a little bit confused about the velocity reconstruction after the pressure solution. U += rAU*fvc::reconstruct((phi - phiU)/rAUf); Why phiU is substracted from the fluxes? phiU is defined as the sum of the predicted velocity interpolated to the faces and the temporal correction. The contribution of H/A is included in the new velocity because of "+=", so which contribution is substructed? Is the temporal correction? thanks again andrea |

Quote:
U -= rUA*fvc::grad(p); thanks for help |

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