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Old   November 25, 2010, 05:25
Default Reg - Log result
  #1
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Hari Krishnan
Join Date: Mar 2009
Location: chennai, Tamil nadu, india
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Dear All,

I am into a calculation of to find out the air volumetric flow rate of a flow path.

To intialize the flow conditions,under simpleFoam, I have followed up these below mentioned relaxation factors.
iteration time 0-300
p - 1e-5, 0.001, 0.8
U - 1e-5, 0 , 0.01
epsilon - 1e-3, 0, 0.01
k - 1e-3, 0, 0.01
R,nutilda - 1e-3,0, 0.01
Inlet presssure, 7000pa, and outlet is 0 pa.

In the 0th time, the k was intialized as 0.0001 and epsilon with 0.01.
By replacing the 300th time to 0th time, iterated to time-4000 with following relaxation factors
p - 1e-6, 0.0001, 0.3
U - 1e-5, 0.001 , 0.4
epsilon - 1e-4, 0.01, 0.4
k - 1e-4, 0.01, 0.4
R,nutilda - 1e-4,0.01, 0.4

But the calulation log result shows the continutiy errors in a abnormal high values

Time = 1

DILUPBiCG: Solving for Ux, Initial residual = 0.0407914, Final residual = 5.31414e-06, No Iterations 3
DILUPBiCG: Solving for Uy, Initial residual = 0.125808, Final residual = 1.32436e-05, No Iterations 3
DILUPBiCG: Solving for Uz, Initial residual = 0.0630549, Final residual = 6.17269e-06, No Iterations 3
GAMG: Solving for p, Initial residual = 0.579967, Final residual = 3.21338e-05, No Iterations 7
time step continuity errors : sum local = 0.182605, global = -0.00299876, cumulative = -0.00299876
DILUPBiCG: Solving for epsilon, Initial residual = 0.165768, Final residual = 0.00011708, No Iterations 2
DILUPBiCG: Solving for k, Initial residual = 0.163874, Final residual = 0.000211085, No Iterations 2
ExecutionTime = 4.44 s ClockTime = 5 s

;

;
Time = 100

DILUPBiCG: Solving for Ux, Initial residual = 0.00241212, Final residual = 4.29667e-06, No Iterations 2
DILUPBiCG: Solving for Uy, Initial residual = 0.00441536, Final residual = 8.43683e-06, No Iterations 2
DILUPBiCG: Solving for Uz, Initial residual = 0.00218416, Final residual = 5.32736e-06, No Iterations 2
GAMG: Solving for p, Initial residual = 0.0230018, Final residual = 1.37452e-06, No Iterations 11
time step continuity errors : sum local = 0.00326717, global = -0.000564809, cumulative = -0.125284
DILUPBiCG: Solving for epsilon, Initial residual = 0.00320255, Final residual = 2.24605e-06, No Iterations 2
DILUPBiCG: Solving for k, Initial residual = 0.00374825, Final residual = 4.17044e-06, No Iterations 2
ExecutionTime = 269.62 s ClockTime = 297 s

;

;

Time = 300

DILUPBiCG: Solving for Ux, Initial residual = 0.00123843, Final residual = 2.41581e-06, No Iterations 2
DILUPBiCG: Solving for Uy, Initial residual = 0.00156465, Final residual = 4.65099e-06, No Iterations 2
DILUPBiCG: Solving for Uz, Initial residual = 0.000839765, Final residual = 3.14799e-06, No Iterations 2
GAMG: Solving for p, Initial residual = 0.00826977, Final residual = 6.9471e-07, No Iterations 9
time step continuity errors : sum local = 0.00204741, global = 0.000325488, cumulative = -0.0805461
DILUPBiCG: Solving for epsilon, Initial residual = 0.00197012, Final residual = 1.65425e-06, No Iterations 2
DILUPBiCG: Solving for k, Initial residual = 0.00200665, Final residual = 2.1513e-06, No Iterations 2
ExecutionTime = 762.05 s ClockTime = 858 s

;

;

Time = 500

DILUPBiCG: Solving for Ux, Initial residual = 0.155768, Final residual = 1.1042e-06, No Iterations 4
DILUPBiCG: Solving for Uy, Initial residual = 0.215307, Final residual = 6.0912e-05, No Iterations 3
DILUPBiCG: Solving for Uz, Initial residual = 0.189597, Final residual = 1.63893e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.521073, Final residual = 3.20929e-05, No Iterations 14
time step continuity errors : sum local = 217.793, global = 40.7283, cumulative = 50.0885
DILUPBiCG: Solving for epsilon, Initial residual = 0.0943214, Final residual = 0.000226612, No Iterations 1
DILUPBiCG: Solving for k, Initial residual = 0.0949947, Final residual = 4.71994e-05, No Iterations 2
ExecutionTime = 1336.27 s ClockTime = 1545 s

;

;

Time = 775

DILUPBiCG: Solving for Ux, Initial residual = 0.313058, Final residual = 7.33734e-05, No Iterations 3
DILUPBiCG: Solving for Uy, Initial residual = 0.362856, Final residual = 7.80359e-05, No Iterations 3
DILUPBiCG: Solving for Uz, Initial residual = 0.271597, Final residual = 3.44234e-05, No Iterations 3
GAMG: Solving for p, Initial residual = 0.493461, Final residual = 4.4403e-05, No Iterations 16
time step continuity errors : sum local = 2.07578e+11, global = -5.99968e+10, cumulative = -4.56283e+10
DILUPBiCG: Solving for epsilon, Initial residual = 0.565744, Final residual = 0.00559245, No Iterations 1
DILUPBiCG: Solving for k, Initial residual = 0.337978, Final residual = 0.00124628, No Iterations 1
ExecutionTime = 2159.84 s ClockTime = 2584 s


The fvscheme was :

ddtSchemes
{
default steadyState;
}

gradSchemes
{
default Gauss linear;
grad(p) Gauss linear;
grad(U) Gauss linear;
}

divSchemes
{
default none;
div(phi,U) Gauss upwind;
div(phi,k) Gauss upwind;
div(phi,epsilon) Gauss upwind;
div(phi,R) Gauss upwind;
div(R) Gauss linear;
div(phi,nuTilda) Gauss upwind;
div((nuEff*dev(grad(U).T()))) Gauss linear;
}

laplacianSchemes
{
default none;
laplacian(nuEff,U) Gauss linear corrected;
laplacian((1|A(U)),p) Gauss linear corrected;
laplacian(DkEff,k) Gauss linear corrected;
laplacian(DepsilonEff,epsilon) Gauss linear limited 0.5;
laplacian(DREff,R) Gauss linear corrected;
laplacian(DnuTildaEff,nuTilda) Gauss linear corrected;
}

interpolationSchemes
{
default linear;
interpolate(U) linear;
}

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p;
}

I had tried by giving the relaxation factors 0.1,0.2,0.2.. for p,u,epsilon.. resp.

Kindly advise me what would the time step continutiy errors high value indicates and how to identify where i would mistake?

Kindly suggest me a solution

Thank you,

Hari
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Old   November 25, 2010, 07:18
Default Reg - Time step continuity error
  #2
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Hari Krishnan
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I am trying to recognize the issue with related to the past threads.

There were previous solutions like changing the fvschemes,fvsolutions, even downscaling etc..

I wont feel those are appropriate to my issue.
When I see the 100,200,300 time iterations in paraview, the flow got stabilised within this 300 time iteration itself when another type of relaxation factors were given.

Any suggestion would be appreciable and helpful for me.

Thank you,

Hari
hariya03 is offline   Reply With Quote

Old   February 15, 2011, 06:32
Default
  #3
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Hari Krishnan
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May I know whether the above mentioned details are not enough for avail solution?

I dont know why is not there a single reply for this topic.

Anyone suggest me.

Thank you,

Hari
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