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December 6, 2012, 11:14 
cavity case in rhoPimpleFoam

#1 
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Ehsan
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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, 13:42 

#2 
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Ehsan
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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 = 2.30733021e07, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 0.002904801618, Final residual = 1.334497056e07, No Iterations 2 DILUPBiCG: Solving for h, Initial residual = 0.00263319834, Final residual = 6.165570932e08, No Iterations 2 DICPCG: Solving for p, Initial residual = 0.004894302097, Final residual = 3.77008551e05, No Iterations 10 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.064078536e07, global = 5.170722179e11, cumulative = 1.229301626e08 rho max/min : 1.158623339 1.158622586 DICPCG: Solving for p, Initial residual = 0.0003231577867, Final residual = 7.031648618e07, No Iterations 14 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 3.856414427e09, global = 5.098053007e11, cumulative = 1.234399679e08 rho max/min : 1.158623339 1.158622586 DILUPBiCG: Solving for omega, Initial residual = 0.0006058053485, Final residual = 2.019874798e06, No Iterations 1 DILUPBiCG: Solving for k, Initial residual = 0.002108742738, Final residual = 5.150541624e06, No Iterations 1 ExecutionTime = 1.46 s ClockTime = 2 s End 

December 11, 2012, 09:13 

#3 
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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, 14:34 

#4 
Senior Member

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)
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December 14, 2012, 04:07 

#5 
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Ehsan
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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, 04:15 

#6  
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Quote:
Quote:
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December 14, 2012, 04:49 

#7  
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Quote:
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, 05:53 

#8  
Senior Member

look at creatFields.H,
rho calculate from another class thermo Quote:
Quote:
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December 14, 2012, 09:55 

#9 
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Ehsan
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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, 06:22 

#10 
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Ehsan
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why sum of continuity cumulative and global are negative?


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