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-   -   cavity case in rhoPimpleFoam (http://www.cfd-online.com/Forums/openfoam-solving/110268-cavity-case-rhopimplefoam.html)

 immortality December 6, 2012 12:14

cavity case in rhoPimpleFoam

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.

 immortality December 6, 2012 14:42

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

 hz283 December 11, 2012 10:13

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

 nimasam December 11, 2012 15:34

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 :D, new rho will be calculated based on previous time step value
(diagonal solver)

 immortality December 14, 2012 05:07

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.

 nimasam December 14, 2012 05:15

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

 hz283 December 14, 2012 05:49

Quote:
 Originally Posted by nimasam (Post 397491) 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. :confused:

 nimasam December 14, 2012 06:53

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

 immortality December 14, 2012 10:55

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?

 immortality January 9, 2013 07:22

why sum of continuity cumulative and global are negative?

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