# rho euation in rhoPisoFoam

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October 2, 2010, 11:48
rho euation in rhoPisoFoam
#1
Senior Member

Nilesh Rane
Join Date: Apr 2010
Posts: 122
Rep Power: 7
Hi,

In rhoPisoFoam, the .c code includes rhoEqn.H file but the file is not in that folder. Is is getting included from some other common directory?? I am asking this because when i solve my simulation the rho equation is not getting solved, it seems.

Can anyone tell me, what is the problem here?? Why the rho equation is not being solved??

Quote:
 Starting time loop Courant Number mean: 0.00160209 max: 0.237358 Time = 1e-06 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 DILUPBiCG: Solving for Ux, Initial residual = 1, Final residual = 2.11628e-11, No Iterations 3 DILUPBiCG: Solving for Uy, Initial residual = 1, Final residual = 1.98311e-11, No Iterations 3 DILUPBiCG: Solving for Uz, Initial residual = 1, Final residual = 1.87167e-09, No Iterations 2 DILUPBiCG: Solving for h, Initial residual = 1, Final residual = 3.93336e-13, No Iterations 2 DICPCG: Solving for p, Initial residual = 1, Final residual = 1.85699e-09, No Iterations 12 DICPCG: Solving for p, Initial residual = 8.61972e-05, Final residual = 2.87593e-10, No Iterations 2 DICPCG: Solving for p, Initial residual = 6.9308e-06, Final residual = 6.70903e-11, No Iterations 2 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.47432e-14, global = -1.96566e-15, cumulative = -1.96566e-15 DILUPBiCG: Solving for h, Initial residual = 0.464004, Final residual = 4.19598e-09, No Iterations 2 DICPCG: Solving for p, Initial residual = 0.0986332, Final residual = 8.95905e-09, No Iterations 10 DICPCG: Solving for p, Initial residual = 2.74445e-05, Final residual = 9.04744e-10, No Iterations 2 DICPCG: Solving for p, Initial residual = 4.60957e-06, Final residual = 7.9637e-09, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 3.76913e-12, global = -3.46891e-13, cumulative = -3.48856e-13 DILUPBiCG: Solving for h, Initial residual = 0.105746, Final residual = 5.79122e-10, No Iterations 2 DICPCG: Solving for p, Initial residual = 0.0235514, Final residual = 5.9246e-09, No Iterations 9 DICPCG: Solving for p, Initial residual = 1.34825e-05, Final residual = 4.20418e-10, No Iterations 2 DICPCG: Solving for p, Initial residual = 4.14208e-06, Final residual = 7.32319e-09, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 3.68586e-12, global = -2.74195e-13, cumulative = -6.23051e-13 DILUPBiCG: Solving for h, Initial residual = 0.0263855, Final residual = 1.16006e-10, No Iterations 2 DICPCG: Solving for p, Initial residual = 0.00641807, Final residual = 4.27544e-09, No Iterations 8 DICPCG: Solving for p, Initial residual = 5.14856e-06, Final residual = 6.37387e-09, No Iterations 1 DICPCG: Solving for p, Initial residual = 2.17279e-06, Final residual = 4.27578e-09, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.18805e-12, global = -1.21706e-13, cumulative = -7.44757e-13
__________________
Imagination is more important than knowledge..

 October 3, 2010, 21:06 #2 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,894 Rep Power: 26 Search your OpenFOAM-1.7.x/src directory for rhoEqn.H and you will find it. It is basically solve(fvm::ddt(rho) + fvc::div(phi)); with explicit discretization of the divergence to avoid conservation errors. The fact you see residuals equal to zero means that the solution is exact, not that the equation is not solved. You are using the diagonal solver, which is direct, and gives you the exact solution of the linear system. Best, sharonyue likes this. __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image. OpenQBMM - An open-source implementation of quadrature-based moment methods

 October 4, 2010, 06:07 #3 Senior Member   Nilesh Rane Join Date: Apr 2010 Posts: 122 Rep Power: 7 But No of iterations is also 0. __________________ Imagination is more important than knowledge..

 October 4, 2010, 12:02 #4 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,894 Rep Power: 26 This is really basic How many iterations do you need to obtain the exact solution of a linear system with a direct solver? The answer is zero, because the method is not iterative You basically can easily do that with the Thomas algorithm for whatever tri-diagonal system (or block tri-diagonal). Check a book on the topic to have the details. Best, __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image. OpenQBMM - An open-source implementation of quadrature-based moment methods

 October 5, 2010, 07:44 #5 Senior Member   Nilesh Rane Join Date: Apr 2010 Posts: 122 Rep Power: 7 Ohh...OF takes it in that sense. I was thinking on different line. I thought if you solve an equation (or rather a system of equations in turn) 1 time then No of Iterations should be 1 and so on... I do know about TDMA.. have used it in my UG assignments.. Thanks a lot.. __________________ Imagination is more important than knowledge..

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