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Old   July 12, 2011, 10:25
Default Momentum predictor
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Andrea Ferrari
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Hi 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());
00003     surfaceScalarField rAUf(fvc::interpolate(rAU));
00004 
00005     U = rAU*UEqn.H();
00006     surfaceScalarField phiU
00007     (
00008         "phiU",
00009         (fvc::interpolate(U) & mesh.Sf())
00010       + fvc::ddtPhiCorr(rAU, rho, U, phi)
00011     );
00012 
00013     adjustPhi(phiU, U, p_rgh);
00014 
00015     phi = phiU +
00016     (
00017         fvc::interpolate(interface.sigmaK())*fvc::snGrad(alpha1)
00018       - ghf*fvc::snGrad(rho)
00019     )*rAUf*mesh.magSf();
what is the difference between switch on or switch off the momentum predictor in uEqn.H and how it affects the predicted velocities?. What does OF calculate in:

Code:
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     }
the second quesiton is: What does it mean
fvc::ddtPhiCorr(rAU, rho, U, phi) in the phiU calculation?

thanks a lot in advance

andrea
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Old   July 19, 2011, 18:52
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Santiago Marquez Damian
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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.
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Santiago MÁRQUEZ DAMIÁN, Ph.D.
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Old   July 20, 2011, 03:49
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Andrea Ferrari
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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 }
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Old   July 20, 2011, 09:29
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Santiago Marquez Damian
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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.
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Santiago MÁRQUEZ DAMIÁN, Ph.D.
Post-doctoral Fellow
Research Center for Computational Mechanics (CIMEC) - CONICET/FICH-UNL
T.E.: 54-342-4511594 Ext. 1005
Güemes 3450 - (3000) Santa Fe
Santa Fe - Argentina
http://www.cimec.org.ar
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Old   July 20, 2011, 09:35
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Ok, now it's totally clear!!

many thanks

andrea
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Old   July 22, 2011, 07:04
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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
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Old   March 11, 2013, 05:09
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Quote:
Originally Posted by Andrea_85 View Post
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
do you find a solution to this question? I'am the same question..i tried to compare it with the PISO algorithm but in the PISO algorithm the this U reconstruction is as follow:
U -= rUA*fvc::grad(p);

thanks for help
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