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Wrong fluctuation of pressure in transient simulation

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Old   February 28, 2015, 00:46
Default Wrong fluctuation of pressure in transient simulation
  #1
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Cai Tao
Join Date: Oct 2014
Location: China shanghai
Posts: 7
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Hi.
I come across a problem in a transient simulation. I use the LES model to simulation a sequare cylinder, and set some pressure monitoring points.
The results of the pressure have a strange fluctuation, which is shown in the follow pictures.


the file of controDict
// ************************************************** *********************** //libs
(

);
application pisoFoam;

startFrom latestTime;

startTime 0;

stopAt endTime;
//stopAt writeNow;

endTime 5;

deltaT 5.0e-6;

writeControl timeStep;

writeInterval 1000;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression off;

timeFormat general;

timePrecision 6;

runTimeModifiable true;

functions
{
probes
{
type probes;
functionObjectLibs ("libsampling.so");
enabled true;
outputControl timeStep;
outputInterval 1;
probeLocations
(
( 0.06 0.02 -0.08 )
( 0.005 0.0095 -0.08 )
( 0.005 0.0305 -0.08 )
( 0.015 0.0095 -0.08 )
( 0.015 0.0305 -0.08 )
}
// ************************************************** *********************** //

the file of fvScheme
// ************************************************** *********************** //
ddtSchemes
{
default backward;
}

d2dt2Schemes
{
}

gradSchemes
{
default Gauss linear;
grad(nuTilda) cellLimited Gauss linear 1;
grad(U) cellLimited Gauss linear 1;
}

divSchemes
{
default none;

div(phi,U) Gauss LUST unlimitedGrad(U);
//div(phi,U) Gauss linearUpwind unlimitedGrad(U);
div(phi,k) Gauss limitedLinear 1;
div(phi,nuTilda) Gauss limitedLinear 1;

div((nuEff*dev(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
default Gauss linear limited corrected 0.33;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default limited corrected 0.33;
}

fluxRequired
{
default no;
p;
}

// ************************************************** *********************** //


the file of fvSolution

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
p
{
solver GAMG;
tolerance 1e-6;
relTol 0.1;
smoother GaussSeidel;
nPreSweeps 0;
nPostSweeps 2;
nFinestSweeps 40;
cacheAgglomeration on;
agglomerator faceAreaPair;
nCellsInCoarsestLevel 128;
mergeLevels 1;
}

pFinal
{
$p;
tolerance 1e-6;
relTol 0;
};

"(U|k|B|nuTilda)"
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-07;
relTol 0.1;
}
"(U|k|B|nuTilda)Final"
{
$U;
tolerance 1e-7;
relTol 0;
};
}

PISO
{
nCorrectors 2;
nNonOrthogonalCorrectors 5;
pRefCell 0;
pRefValue 0;
}

relaxationFactors
{
"U.*" 1;
"p.*" 1;
"nuTilda.*" 1;
}
// ************************************************** *********************** //
part of the file of the log



Time = 0.12566

Courant Number mean: 0.00839828 max: 0.310058
smoothSolver: Solving for Ux, Initial residual = 3.6145e-05, Final residual = 1.33368e-07, No Iterations 1
smoothSolver: Solving for Uy, Initial residual = 0.00041477, Final residual = 1.43826e-06, No Iterations 1
smoothSolver: Solving for Uz, Initial residual = 0.00079561, Final residual = 3.29873e-06, No Iterations 1
GAMG: Solving for p, Initial residual = 0.00910454, Final residual = 0.000548275, No Iterations 1
GAMG: Solving for p, Initial residual = 0.002062, Final residual = 0.000200861, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00120839, Final residual = 9.88252e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000657611, Final residual = 6.04321e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000334683, Final residual = 2.98511e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.000201084, Final residual = 1.9542e-05, No Iterations 3
time step continuity errors : sum local = 1.57267e-11, global = -3.70403e-14, cumulative = 2.7449e-12
GAMG: Solving for p, Initial residual = 0.00336111, Final residual = 0.00018496, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00165023, Final residual = 0.0001041, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000837023, Final residual = 6.35304e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000429824, Final residual = 4.20207e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000238282, Final residual = 2.09567e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.000144679, Final residual = 9.81141e-07, No Iterations 80
time step continuity errors : sum local = 8.19777e-13, global = -3.70403e-14, cumulative = 2.70786e-12
ExecutionTime = 6263.22 s ClockTime = 6361 s

Time = 0.125665

Courant Number mean: 0.00839835 max: 0.310065
smoothSolver: Solving for Ux, Initial residual = 3.61455e-05, Final residual = 1.33319e-07, No Iterations 1
smoothSolver: Solving for Uy, Initial residual = 0.000414767, Final residual = 1.43823e-06, No Iterations 1
smoothSolver: Solving for Uz, Initial residual = 0.000795566, Final residual = 3.29825e-06, No Iterations 1
GAMG: Solving for p, Initial residual = 0.00916193, Final residual = 0.0005405, No Iterations 1
GAMG: Solving for p, Initial residual = 0.00205039, Final residual = 0.00019946, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00118592, Final residual = 9.89506e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000645054, Final residual = 6.05196e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000332466, Final residual = 3.01745e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.000198621, Final residual = 1.98006e-05, No Iterations 3
time step continuity errors : sum local = 1.59175e-11, global = 6.0819e-14, cumulative = 2.76868e-12
GAMG: Solving for p, Initial residual = 0.00335465, Final residual = 0.000184149, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00164526, Final residual = 0.000104069, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000834565, Final residual = 6.34114e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000428368, Final residual = 4.17622e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000237407, Final residual = 2.04899e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.00014399, Final residual = 9.93928e-07, No Iterations 77
time step continuity errors : sum local = 8.52212e-13, global = 6.0819e-14, cumulative = 2.8295e-12
ExecutionTime = 6310.82 s ClockTime = 6409 s

Time = 0.12567

Courant Number mean: 0.00839843 max: 0.310072
smoothSolver: Solving for Ux, Initial residual = 3.61467e-05, Final residual = 1.33373e-07, No Iterations 1
smoothSolver: Solving for Uy, Initial residual = 0.000414775, Final residual = 1.43828e-06, No Iterations 1
smoothSolver: Solving for Uz, Initial residual = 0.000795495, Final residual = 3.29769e-06, No Iterations 1
GAMG: Solving for p, Initial residual = 0.0091657, Final residual = 0.00054717, No Iterations 1
GAMG: Solving for p, Initial residual = 0.00205872, Final residual = 0.000199804, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00120643, Final residual = 9.84e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000656809, Final residual = 6.01974e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000334246, Final residual = 2.96852e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.000200805, Final residual = 1.95013e-05, No Iterations 3
time step continuity errors : sum local = 1.56932e-11, global = -3.71509e-14, cumulative = 2.79235e-12
GAMG: Solving for p, Initial residual = 0.00336065, Final residual = 0.000184732, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00164948, Final residual = 0.000103936, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000836544, Final residual = 6.33963e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000429508, Final residual = 4.19258e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00023813, Final residual = 2.08646e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.00014451, Final residual = 9.97118e-07, No Iterations 79
time step continuity errors : sum local = 8.31101e-13, global = -3.71509e-14, cumulative = 2.75519e-12
ExecutionTime = 6358.9 s ClockTime = 6457 s

Time = 0.125675

Courant Number mean: 0.0083985 max: 0.310079
smoothSolver: Solving for Ux, Initial residual = 3.61467e-05, Final residual = 1.33325e-07, No Iterations 1
smoothSolver: Solving for Uy, Initial residual = 0.000414768, Final residual = 1.43821e-06, No Iterations 1
smoothSolver: Solving for Uz, Initial residual = 0.00079544, Final residual = 3.29733e-06, No Iterations 1
GAMG: Solving for p, Initial residual = 0.00908316, Final residual = 0.000539338, No Iterations 1
GAMG: Solving for p, Initial residual = 0.00204978, Final residual = 0.000199266, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00118581, Final residual = 9.87077e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000644816, Final residual = 6.03733e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000332293, Final residual = 3.01533e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.000198653, Final residual = 1.98122e-05, No Iterations 3
time step continuity errors : sum local = 1.59243e-11, global = 6.10176e-14, cumulative = 2.81621e-12
GAMG: Solving for p, Initial residual = 0.00335482, Final residual = 0.000184184, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00164542, Final residual = 0.000104145, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000834698, Final residual = 6.35111e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000428487, Final residual = 4.18969e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000237558, Final residual = 2.06722e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.000144187, Final residual = 9.92679e-07, No Iterations 79
time step continuity errors : sum local = 8.51382e-13, global = 6.10176e-14, cumulative = 2.87723e-12
ExecutionTime = 6407.22 s ClockTime = 6506 s

Time = 0.12568

Courant Number mean: 0.00839857 max: 0.310086
smoothSolver: Solving for Ux, Initial residual = 3.61473e-05, Final residual = 1.33375e-07, No Iterations 1
smoothSolver: Solving for Uy, Initial residual = 0.000414769, Final residual = 1.43821e-06, No Iterations 1
smoothSolver: Solving for Uz, Initial residual = 0.000795392, Final residual = 3.29701e-06, No Iterations 1
GAMG: Solving for p, Initial residual = 0.00903316, Final residual = 0.000545484, No Iterations 1
GAMG: Solving for p, Initial residual = 0.00205756, Final residual = 0.000199936, No Iterations 2
GAMG: Solving for p, Initial residual = 0.0012069, Final residual = 9.83739e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000657011, Final residual = 6.01633e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000334339, Final residual = 2.97385e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.000200948, Final residual = 1.94727e-05, No Iterations 3
time step continuity errors : sum local = 1.56695e-11, global = -3.72636e-14, cumulative = 2.83997e-12
GAMG: Solving for p, Initial residual = 0.00336013, Final residual = 0.000184686, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00164964, Final residual = 0.00010392, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000836632, Final residual = 6.34008e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000429559, Final residual = 4.19243e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000238137, Final residual = 2.08849e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.000144556, Final residual = 9.82253e-07, No Iterations 79
time step continuity errors : sum local = 8.19351e-13, global = -3.72636e-14, cumulative = 2.8027e-12
ExecutionTime = 6455.37 s ClockTime = 6554 s

Time = 0.125685

Courant Number mean: 0.00839865 max: 0.310093
smoothSolver: Solving for Ux, Initial residual = 3.61477e-05, Final residual = 1.33329e-07, No Iterations 1
smoothSolver: Solving for Uy, Initial residual = 0.000414766, Final residual = 1.43816e-06, No Iterations 1
smoothSolver: Solving for Uz, Initial residual = 0.000795332, Final residual = 3.29664e-06, No Iterations 1
GAMG: Solving for p, Initial residual = 0.00902425, Final residual = 0.000538001, No Iterations 1
GAMG: Solving for p, Initial residual = 0.00204822, Final residual = 0.000198808, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00118526, Final residual = 9.88807e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000645015, Final residual = 6.0607e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000332475, Final residual = 3.02826e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.000198705, Final residual = 1.66574e-05, No Iterations 4
time step continuity errors : sum local = 1.34104e-11, global = 6.12341e-14, cumulative = 2.86394e-12
GAMG: Solving for p, Initial residual = 0.0033574, Final residual = 0.00018402, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00164436, Final residual = 0.000103905, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000834272, Final residual = 6.33415e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000428371, Final residual = 4.17247e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000237515, Final residual = 2.0474e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.000144517, Final residual = 9.88653e-07, No Iterations 77
time step continuity errors : sum local = 8.48563e-13, global = 6.12341e-14, cumulative = 2.92517e-12
ExecutionTime = 6500.77 s ClockTime = 6601 s

actually, I have once slove this problem by change the mesh, see the post "A shock appears after several periods of the transient simulation"http://www.cfd-online.com/Forums/openfoam-solving/143751-shock-

appears-after-several-periods-transient-simulation.html. but now, this method seems useless. Can someone come across such problem. maybe we can have a disscussion.
Attached Images
File Type: jpg QQ??20150228103550.jpg (23.0 KB, 19 views)
File Type: jpg QQ??20150228121234.jpg (63.9 KB, 21 views)
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Old   February 28, 2015, 09:33
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  #2
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anonymous
Join Date: Aug 2014
Posts: 175
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Maybe you should let te simulation run for a lot more of time. I don't think that it has had enough time to settle.

If you've already tried it, we could dip in it further
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Old   March 5, 2015, 22:33
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Cai Tao
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Quote:
Originally Posted by ssss View Post
Maybe you should let te simulation run for a lot more of time. I don't think that it has had enough time to settle.

If you've already tried it, we could dip in it further
hi anonymous
I have run this case form time 0.125s to 0.24s, and the result is still unsatisfactory. The attached pictures are the result. Do you think I need to keep runing this case? or maybe I need to change some sets?
Attached Images
File Type: jpg QQ??20150306100853.jpg (25.7 KB, 6 views)
File Type: jpg QQ??20150306101004.jpg (50.4 KB, 4 views)
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pressure, transient simulation, wrong fluctuation

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