# cavity case in rhoPimpleFoam

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 December 6, 2012, 12:14 cavity case in rhoPimpleFoam #1 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,210 Rep Power: 19 at the cavity case in rhoPimpleFoam folder occurs something odd! and that is when it is running residual of rho is zero in command shell from start to end and in paraView also the pressure and velocity fields are not like icoFoam test case at all. why it is so? can anyone think about and tell me? thanks.

 December 6, 2012, 14:42 #2 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,210 Rep Power: 19 this is a time step(it seems rho is not solved): Courant Number mean: 0.1716988131 max: 0.5466230657 Time = 2 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 DILUPBiCG: Solving for Ux, Initial residual = 0.002584181588, Final residual = 2.30733021e-07, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 0.002904801618, Final residual = 1.334497056e-07, No Iterations 2 DILUPBiCG: Solving for h, Initial residual = 0.00263319834, Final residual = 6.165570932e-08, No Iterations 2 DICPCG: Solving for p, Initial residual = 0.004894302097, Final residual = 3.77008551e-05, No Iterations 10 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.064078536e-07, global = -5.170722179e-11, cumulative = -1.229301626e-08 rho max/min : 1.158623339 1.158622586 DICPCG: Solving for p, Initial residual = 0.0003231577867, Final residual = 7.031648618e-07, No Iterations 14 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 3.856414427e-09, global = -5.098053007e-11, cumulative = -1.234399679e-08 rho max/min : 1.158623339 1.158622586 DILUPBiCG: Solving for omega, Initial residual = 0.0006058053485, Final residual = 2.019874798e-06, No Iterations 1 DILUPBiCG: Solving for k, Initial residual = 0.002108742738, Final residual = 5.150541624e-06, No Iterations 1 ExecutionTime = 1.46 s ClockTime = 2 s End

 December 11, 2012, 10:13 #3 Senior Member   Join Date: Nov 2012 Posts: 168 Rep Power: 6 Hi, I found that I have the same problem when I used the solve rhoPimpleFoam . the Initial residual, final residual and iterations are all zero. Do you have got the cause for this issue? Thank you very much. best regards, hz

 December 11, 2012, 15:34 #4 Senior Member   Nima Samkhaniani Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,233 Blog Entries: 1 Rep Power: 18 Atleast in two posts in this forum, i saw the answer of this question, it solves equation in explicit manner, so there is no residual , new rho will be calculated based on previous time step value (diagonal solver) __________________ Telegram channel (https://telegram.me/openfoam4Iranian) My Weblog in Persian(http://openfoam.blogfa.com/) My Personal Website (http://nimasamkhaniani.ir/)

 December 14, 2012, 05:07 #5 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,210 Rep Power: 19 yes some one that has a lot of kind has answered before.totally here all are kindful together and dont reproach eachother for replying.however then why these residuals are shown at the results when they are all zero.as i know in rhoCentralFoam density should be calculated implicitly from continuity.correct if needs.

December 14, 2012, 05:15
#6
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Nima Samkhaniani
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Quote:
 .as i know in rhoCentralFoam density should be calculated implicitly from continuity
why ? from where?
Quote:
 solve(fvm::ddt(rho) + fvc::div(phi));
from code, it is clear that it calculates rho explicitly
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December 14, 2012, 05:49
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Quote:
 Originally Posted by nimasam why ? from where? from code, it is clear that it calculates rho explicitly
Hi,

thank you for your help. When the simulation starts, in the first step, where does the code get the initial values of rho and phi(=rho*U*A)? because I found that we did not need to initialize the density in the folder 0/. Thank you very much.

December 14, 2012, 06:53
#8
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Nima Samkhaniani
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look at creatFields.H,

rho calculate from another class thermo
Quote:
 volScalarField rho ( IOobject ( "rho", runTime.timeName(), mesh, IOobject::NO_READ, IOobject::AUTO_WRITE ), thermo.rho(), rhoBoundaryTypes );
and phi is :
Quote:
 surfaceScalarField phi("phi", mesh.Sf() & fvc::interpolate(rhoU));
you need to read the code
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 December 14, 2012, 10:55 #9 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,210 Rep Power: 19 i accept the reality of approach but my argument is on the truth means what should be or is more rational to be in existance.therefore in your opinion what will be difference between a density based scheme and pressure one when both calculate rho explicitly and at the other hand what is the necessity for displaying and printing these zero and zero numbers from starting to end.i know we can disable writing of those by changing solver but what intentions do the providers have got?does exist a rational explanation for this behaviour?

 January 9, 2013, 07:22 #10 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,210 Rep Power: 19 why sum of continuity cumulative and global are negative?

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