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pimpleFoam runs slower than rhoPimpleFoam

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Old   February 5, 2020, 22:39
Default pimpleFoam runs slower than rhoPimpleFoam
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Kosuke Seto
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Hi,

I'm trying to simulate the low Mach number flow.

I firstly use pimpleFoam because of the low Mach number, but it was so slow.
Then, I started to use rhoPimpleFoam and it ran faster.

Becouse rhoPimpleFoam needs to solve rho, but pimpleFoam needn't, I first ly thought that PimpleFoam runs faster, but it didn't.

Here's the log file of each solver.
Used geometry, deltaT and runTime are the same.
These are the part of last time step of each.

rhoPimpleFoam
Code:
Courant Number mean: 0.036513 max: 4.87821
Time = 0.001

PIMPLE: iteration 1
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
DILUPBiCG:  Solving for Ux, Initial residual = 0.00647503, Final residual = 4.47952e-08, No Iterations 1
DILUPBiCG:  Solving for Uy, Initial residual = 0.00802886, Final residual = 1.79069e-06, No Iterations 2
DILUPBiCG:  Solving for e, Initial residual = 0.00460524, Final residual = 1.584e-08, No Iterations 1
DICPCG:  Solving for p, Initial residual = 0.0134054, Final residual = 5.03037e-07, No Iterations 6
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 4.07381e-09, global = 8.16074e-10, cumulative = 4.08312e-07
PIMPLE: iteration 2
DILUPBiCG:  Solving for Ux, Initial residual = 0.00189279, Final residual = 3.3992e-08, No Iterations 1
DILUPBiCG:  Solving for Uy, Initial residual = 0.00242582, Final residual = 2.28783e-07, No Iterations 3
DILUPBiCG:  Solving for e, Initial residual = 0.00146006, Final residual = 1.41675e-08, No Iterations 1
DICPCG:  Solving for p, Initial residual = 0.00106469, Final residual = 9.15342e-07, No Iterations 2
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 7.46023e-09, global = 2.165e-09, cumulative = 4.10477e-07
PIMPLE: iteration 3
DILUPBiCG:  Solving for Ux, Initial residual = 0.000564564, Final residual = 3.10279e-08, No Iterations 1
DILUPBiCG:  Solving for Uy, Initial residual = 0.000729992, Final residual = 2.123e-08, No Iterations 3
DILUPBiCG:  Solving for e, Initial residual = 0.000476872, Final residual = 2.00902e-08, No Iterations 1
DICPCG:  Solving for p, Initial residual = 0.000348436, Final residual = 6.79079e-07, No Iterations 4
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 5.53697e-09, global = 2.12568e-10, cumulative = 4.10689e-07
DILUPBiCG:  Solving for k, Initial residual = 0.00107901, Final residual = 8.67088e-08, No Iterations 1
bounding k, min: 0 max: 4.79338 average: 0.0456554
ExecutionTime = 202.8 s  ClockTime = 202 s

fieldAverage fieldAverage1 write:
    Calculating averages

    Writing average fields

End
pimpleFoam
Code:
Courant Number mean: 0.0358382 max: 5.41205

Time = 0.001



PIMPLE: iteration 1

DILUPBiCG:  Solving for Ux, Initial residual = 2.28422e-05, Final residual = 2.1461e-07, No Iterations 1

DILUPBiCG:  Solving for Uy, Initial residual = 0.000813427, Final residual = 2.42374e-07, No Iterations 2

DICPCG:  Solving for p, Initial residual = 0.00736801, Final residual = 7.23368e-05, No Iterations 94

time step continuity errors : sum local = 6.35008e-11, global = 1.2066e-12, cumulative = -2.96628e-08

PIMPLE: iteration 2

DILUPBiCG:  Solving for Ux, Initial residual = 7.86165e-06, Final residual = 7.83411e-08, No Iterations 1

DILUPBiCG:  Solving for Uy, Initial residual = 0.000297705, Final residual = 8.88551e-07, No Iterations 2

DICPCG:  Solving for p, Initial residual = 0.00674716, Final residual = 6.64599e-05, No Iterations 84

time step continuity errors : sum local = 5.84091e-11, global = 7.84435e-13, cumulative = -2.9662e-08

PIMPLE: iteration 3

DILUPBiCG:  Solving for Ux, Initial residual = 2.6318e-06, Final residual = 2.6861e-08, No Iterations 1

DILUPBiCG:  Solving for Uy, Initial residual = 0.000100458, Final residual = 7.50726e-08, No Iterations 2

DICPCG:  Solving for p, Initial residual = 0.00350058, Final residual = 3.48472e-05, No Iterations 105

time step continuity errors : sum local = 3.06619e-11, global = 3.39332e-12, cumulative = -2.96586e-08

DILUPBiCG:  Solving for nuTilda, Initial residual = 0.000401555, Final residual = 3.25482e-06, No Iterations 1

ExecutionTime = 405.13 s  ClockTime = 406 s



fieldAverage fieldAverage1 write:

    Calculating averages



    Writing average fields



End

I check them and realized that NO Iterations of P is much larger in pimpleFoam resulting in ClockTime in pimpleFoam is twice as that in rhoPimpleFoam.

Perhaps I don't understand the difference of algorithm in each solver very much, so I can't identify the cause of this.
I wanna use also pimpleFoam futuristic, so can anyone tell me why and how to solve this.


Thank you for any help you can provide!
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Old   February 6, 2020, 01:50
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Yogesh Bapat
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You can try to use GAMG for p and smoothSolver for U and turbulence parameters.
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Old   February 6, 2020, 02:14
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Kosuke Seto
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Thans for replying,Yogesh!

I'll try it and share the result here.

I still have some questions.
I think that the change of solver may have some effect, but it is not appropriate to comprehend the difference of two solver.
Do you have any opinion?

Best regards.
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Old   May 27, 2023, 14:12
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Alireza Maleki
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Hi, did you find out the reason why pimpleFoam need much more iteration in solving the pressure?

I have the same issue in comparison to rhopimpleFoam and pimpleFoam!
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