[baran_foam]

Greeting all,
I am trying to implement viewFactor radiation model in chtMultiRegionFoam My geometry is a cavity air surrounded by solid insulation..inside cavity there is heating element giving constant temperature bc ..
but may be it some problem increating viewfactor generation matrix...so for low thermal conductivity say 0.2 it is diverging showing the error

--> FOAM FATAL ERROR:
Maximum number of iterations exceeded

for other thermal conductivity..it is showing...
"floating point exception"

Another issue is that..from first iteration in solid insulation temperature went negative...

Constructed constSolidThermo with
rho : rho [1 -3 0 0 0 0 0] 200
Cp : Cp [0 2 -2 -1 0 0 0] 1050
K : K [1 1 -3 -1 0 0 0] 0.2
Hf : Hf [0 2 -2 0 0 0 0] 0
emissivity : emissivity [0 0 0 0 0 0 0] 0.7
kappa : kappa [0 -1 0 0 0 0 0] 0
sigmaS : sigmaS [0 -1 0 0 0 0 0] 0

Time = 1


Solving for fluid region cavityAir
DILUPBiCG: Solving for Ux, Initial residual = 1, Final residual = 0.003580486, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 1, Final residual = 0.01333478, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 1, Final residual = 0.01962788, No Iterations 1
DILUPBiCG: Solving for h, Initial residual = 1, Final residual = 0.0410498, No Iterations 1

Decomposing C matrix...

LU Back substitute C matrix..
Min/max T:300 600
GAMG: Solving for p_rgh, Initial residual = 0.9989019, Final residual = 0.00930975, No Iterations 8
time step continuity errors : sum local = 9.485214e-05, global = 4.571069e-18, cumulative = 4.571069e-18
Min/max rho:0.5793113 1.158623
DILUPBiCG: Solving for omega, Initial residual = 0.1996194, Final residual = 0.003220218, No Iterations 1
DILUPBiCG: Solving for k, Initial residual = 0.9999999, Final residual = 0.04957684, No Iterations 1

Solving for solid region consT
DICPCG: Solving for T, Initial residual = 1, Final residual = 0.02127867, No Iterations 1
Min/max T:-229.3226 2868.877

Solving for solid region front
DICPCG: Solving for T, Initial residual = 1, Final residual = 0.009178718, No Iterations 2
Min/max T:272.8339 352.6411

Solving for solid region back
DICPCG: Solving for T, Initial residual = 1, Final residual = 0.008672207, No Iterations 2
Min/max T:197.2785 436.24
ExecutionTime = 306.09 s ClockTime = 307 s

Time = 2


Solving for fluid region cavityAir
DILUPBiCG: Solving for Ux, Initial residual = 0.9287885, Final residual = 0.01239605, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.696164, Final residual = 0.008070762, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.725314, Final residual = 0.009405048, No Iterations 1
DILUPBiCG: Solving for h, Initial residual = 0.7776453, Final residual = 0.02300447, No Iterations 1
Min/max T:-229.3226 2868.877
GAMG: Solving for p_rgh, Initial residual = 0.9800538, Final residual = 0.007261345, No Iterations 3
time step continuity errors : sum local = 6.842853, global = -1.089344e-14, cumulative = -1.088887e-14
Min/max rho:0.2 2
DILUPBiCG: Solving for omega, Initial residual = 0.003765011, Final residual = 0.0001824057, No Iterations 1
DILUPBiCG: Solving for k, Initial residual = 0.9616083, Final residual = 0.02695649, No Iterations 1

Solving for solid region consT
DICPCG: Solving for T, Initial residual = 0.24694, Final residual = 0.01181695, No Iterations 1
Min/max T:0.5520173 1237.833

Solving for solid region front
DICPCG: Solving for T, Initial residual = 0.1621441, Final residual = 0.01108482, No Iterations 1
Min/max T:256.9791 366.2241

Solving for solid region back
DICPCG: Solving for T, Initial residual = 0.3003714, Final residual = 0.02406933, No Iterations 1
Min/max T:153.0796 428.1253
ExecutionTime = 307.19 s ClockTime = 308 s

Kindly can anyone suggest what is the problem with this issue?

Regards,
baran

[cliffoi]

Hi Baran,
I'm a little out of date but, based on previous experience and a quick scan of the latest source code for OpenFOAM 2.3.0, the view factor radiation model in OpenFOAM is fully explicit. What this essentially means is that, for problems where radiation is important, instabilities are likely. This is particularly problematic in steady-state problems. My first suggestion is to try applying relaxation to the radiation heat source "Qr" and/or the temperature T and increase the number of temperature correction iterations.

I hope this is helpful
Ivor

[baran_foam]

Greeting all,
@Ivor ..thankss for your suggestion...
I have made the under relaxation in this way....
for Fluid region

SIMPLE
{
momentumPredictor on;
nNonOrthogonalCorrectors 0;
pRefCell 0;
pRefValue 100000;
rhoMin rhoMin [1 -3 0 0 0] 0.2;
rhoMax rhoMax [1 -3 0 0 0] 2;
}

relaxationFactors
{
fields
{
rho 0.1;
p_rgh 0.1;
}
equations
{
U 0.1;
h 0.1;
"(k|epsilon|omega)" 0.1;
G 0.1;
"ILambda.*" 0.1;
Qr 0.1;
}

for Solid region

SIMPLE
{
nNonOrthogonalCorrectors 0;
}

relaxationFactors
{
fields
{
}
equations
{
T 0.1;
}
}

I have no idea, how to increase temperature correction iteration...??

Still it is diverging.....
From 1st iteration only it calculate wrong value....

Selecting radiationModel viewFactor
Selecting absorptionEmissionModel constantAbsorptionEmission
Selecting scatterModel constantScatter
Total number of clusters : 6916
Insert elements in the matrix...
Smoothing the matrix...
*** Reading solid mesh thermophysical properties for region consT

Adding to thermos

Constructed constSolidThermo with
rho : rho [1 -3 0 0 0 0 0] 200
Cp : Cp [0 2 -2 -1 0 0 0] 1050
K : K [1 1 -3 -1 0 0 0] 0.2
Hf : Hf [0 2 -2 0 0 0 0] 0
emissivity : emissivity [0 0 0 0 0 0 0] 0.7
kappa : kappa [0 -1 0 0 0 0 0] 0
sigmaS : sigmaS [0 -1 0 0 0 0 0] 0

*** Reading solid mesh thermophysical properties for region front

Adding to thermos

Constructed constSolidThermo with
rho : rho [1 -3 0 0 0 0 0] 200
Cp : Cp [0 2 -2 -1 0 0 0] 1050
K : K [1 1 -3 -1 0 0 0] 0.2
Hf : Hf [0 2 -2 0 0 0 0] 0
emissivity : emissivity [0 0 0 0 0 0 0] 0.7
kappa : kappa [0 -1 0 0 0 0 0] 0
sigmaS : sigmaS [0 -1 0 0 0 0 0] 0

*** Reading solid mesh thermophysical properties for region back

Adding to thermos

Constructed constSolidThermo with
rho : rho [1 -3 0 0 0 0 0] 200
Cp : Cp [0 2 -2 -1 0 0 0] 1050
K : K [1 1 -3 -1 0 0 0] 0.2
Hf : Hf [0 2 -2 0 0 0 0] 0
emissivity : emissivity [0 0 0 0 0 0 0] 0.7
kappa : kappa [0 -1 0 0 0 0 0] 0
sigmaS : sigmaS [0 -1 0 0 0 0 0] 0

Time = 1


Solving for fluid region cavityAir
DILUPBiCG: Solving for Ux, Initial residual = 1, Final residual = 0.0002933064, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 1, Final residual = 0.00187239, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 1, Final residual = 0.002445057, No Iterations 1
DILUPBiCG: Solving for h, Initial residual = 1, Final residual = 0.0002107808, No Iterations 1

Decomposing C matrix...

LU Back substitute C matrix..
Min/max T:300 600
GAMG: Solving for p_rgh, Initial residual = 0.999703, Final residual = 0.009477161, No Iterations 8
time step continuity errors : sum local = 9.480888e-05, global = 3.806627e-18, cumulative = 3.806627e-18
Min/max rho:0.5793113 1.158623
DILUPBiCG: Solving for omega, Initial residual = 0.01985466, Final residual = 5.478545e-06, No Iterations 1
DILUPBiCG: Solving for k, Initial residual = 0.9999963, Final residual = 0.0004892097, No Iterations 1

Solving for solid region consT
DICPCG: Solving for T, Initial residual = 1, Final residual = 0.0004817332, No Iterations 1
Min/max T:-1098.868 1973.284

Solving for solid region front
DICPCG: Solving for T, Initial residual = 1, Final residual = 0.001541441, No Iterations 1
Min/max T:286.249 322.0137

Solving for solid region back
DICPCG: Solving for T, Initial residual = 1, Final residual = 0.001264182, No Iterations 1
Min/max T:227.1158 393.1771
ExecutionTime = 332.8 s ClockTime = 333 s

Time = 2


Solving for fluid region cavityAir
DILUPBiCG: Solving for Ux, Initial residual = 0.8267655, Final residual = 0.001452099, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.4513263, Final residual = 0.0005810657, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.4508985, Final residual = 0.0007290486, No Iterations 1
DILUPBiCG: Solving for h, Initial residual = 0.4400378, Final residual = 7.240746e-05, No Iterations 1
Min/max T:-1098.868 1973.284
GAMG: Solving for p_rgh, Initial residual = 0.9984738, Final residual = 0.008052426, No Iterations 2
time step continuity errors : sum local = 0.1321462, global = 4.714019e-16, cumulative = 4.752085e-16
Min/max rho:0.5791954 1.24276
DILUPBiCG: Solving for omega, Initial residual = 4.942994e-06, Final residual = 9.953325e-09, No Iterations 1
DILUPBiCG: Solving for k, Initial residual = 0.1724617, Final residual = 4.574731e-05, No Iterations 1

Solving for solid region consT
DICPCG: Solving for T, Initial residual = 0.2005355, Final residual = 0.000149245, No Iterations 1
Min/max T:2.205111 427.4738

Solving for solid region front
DICPCG: Solving for T, Initial residual = 0.1542511, Final residual = 0.0002249493, No Iterations 1
Min/max T:285.0157 323.4353

Solving for solid region back
DICPCG: Solving for T, Initial residual = 0.3187484, Final residual = 0.0003813551, No Iterations 1
Min/max T:208.5377 369.8918
ExecutionTime = 333.96 s ClockTime = 335 s

So how to tackle this issue..can anyone suggest??

Regards,
baran

[cliffoi]

Hi Baran,
You haven't given much information on the errors given during the radiation calculation. It's not clear which part of the solver is giving that error. Could you post the full output?

In relation to the instability in solid region temperatures:

• Is this is a transient solution (chtMuliRegionFoam and not chtMultiRegionSimpleFoam). If time-dependent, then the temperature instabilities are unexpected. Try reducing the time step size. Increase the number of PIMPLE correctors.
• Is the solution stable with thermal radiation switched off?
• It looks like the region consT is giving unbounded solutions. Try relaxing the temperature equation in this region.

If you send me the case, I can see if I can find a way forward for you.

Regards
Ivor

[baran_foam]

Greeting all,
@ Ivor...
this is a steady state case... chtMultiregionSimpleFoam
fluidZone.... cavityAir
solidZone....front, back, consT
It is working when radiation is switch off....
This is my case file for radiation...
https://www.dropbox.com/s/96y3woxakt...ation.zip?dl=0

What is the feature angle in viewFactor Dict file....??
Output file is also attached here.......
regards,
baran

[chriss85]

Can you post your fvSolution file? Your log files look as if you use a too high residual for the matrix solvers (only 1 iteration, high final residuals). I don't have any experience with the viewFactor radiation model myself.

[baran_foam]

this attached for one solid region and one for fluid....
https://www.dropbox.com/s/t5p1mte134...ution.zip?dl=0
regards,
baran

[wc34071209]

I would say that you'd better decrease the number of 'nFacesInCoarsestLevel' in dictionary file 'viewFactorsDict' located under 'constant'.

[baran_foam]

Greeting all,
I have some doubt regarding viewFactor radiation model....
1. What kind of effect we get if change 'nFacesInCoarsestLevel' in dictionary file 'viewFactorsDict' located under 'constant'??

2.What is the meaning of featureAngle in "viewFactorsDict" file...?
Mostly this feature angle option is not there in Fluent....

@cong thanks for your suggestions...
but I tried with these combination of

nFacesInCoarsestLevel 20;
featureAngle 10;

nFacesInCoarsestLevel 40;
featureAngle 10;

nFacesInCoarsestLevel 10;
featureAngle 10;

nFacesInCoarsestLevel 10;
featureAngle 1;

still same issue is coming...after that it is diverged......

Regards,
baran

[wc34071209]

Originally Posted by baran_foam

Greeting all,
I have some doubt regarding viewFactor radiation model....
1. What kind of effect we get if change 'nFacesInCoarsestLevel' in dictionary file 'viewFactorsDict' located under 'constant'??

2.What is the meaning of featureAngle in "viewFactorsDict" file...?
Mostly this feature angle option is not there in Fluent....

@cong thanks for your suggestions...
but I tried with these combination of





still same issue is coming...after that it is diverged......

Regards,
baran

You are using OF2.1. Please try OF2.3. It seems it is not because of viewFactor radiation model but something else.

[cliffoi]

I tried to run the attached case without any success. I couldn't even figure out what version of OpenFOAM you're using. I tried 2.2, 2.3 and the extend versions, all without success.

The feature angle and number of coarsest faces are used for agglomerating the faces for the view factor radiation calculation. Since the calculation involves NxN dense matrix inversions and multiplications, it can get really big really quickly. The idea is to agglomerate faces into groups to reduce the size of the problem. The feature angle is used to help ensure that the agglomerated faces share a common flat surface, i.e. helps to make sure the face grouping makes some physical sense.
I agree with Cong though. There is no reason to suggest that the problem is specifically related to the radiation model.
My suggestion is as follows. Set up the case without any radiation. If you need to run it with lower heater power to achieve this, then do this. Once you have a stable conjugate heat transfer solution then you can think about introducing the radiation model.

[baran_foam]

@ ivor....this openFoam versioon is 2.1.....
the case is runing properly without radiation.....after 15000 iteration residual is like this...

Time = 14998


Solving for fluid region cavityAir
DILUPBiCG: Solving for Ux, Initial residual = 0.0171211, Final residual = 0.0002174334, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.01850828, Final residual = 0.0002258723, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.01649942, Final residual = 0.000220407, No Iterations 1
DILUPBiCG: Solving for h, Initial residual = 0.002218244, Final residual = 2.974545e-05, No Iterations 2
Min/max T:358.2003 570.9645
GAMG: Solving for p_rgh, Initial residual = 0.03521581, Final residual = 0.0002197859, No Iterations 3
time step continuity errors : sum local = 0.006952361, global = 6.708561e-13, cumulative = -2.715702e-10
Min/max rho:0.9396181 1.497788
DILUPBiCG: Solving for omega, Initial residual = 7.257771e-05, Final residual = 1.595808e-06, No Iterations 1
DILUPBiCG: Solving for k, Initial residual = 0.008809298, Final residual = 0.0002710091, No Iterations 1

Solving for solid region consT
DICPCG: Solving for T, Initial residual = 4.466364e-06, Final residual = 4.27971e-07, No Iterations 1
Min/max T:303.0746 498.7842

Solving for solid region front
DICPCG: Solving for T, Initial residual = 1.732798e-06, Final residual = 1.288172e-07, No Iterations 1
Min/max T:303.6354 437.2566

Solving for solid region back
DICPCG: Solving for T, Initial residual = 1.875931e-06, Final residual = 1.381792e-07, No Iterations 1
Min/max T:303.6258 437.5337
ExecutionTime = 21754.83 s ClockTime = 21759 s

Time = 14999


Solving for fluid region cavityAir
DILUPBiCG: Solving for Ux, Initial residual = 0.01760132, Final residual = 0.0002245388, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.01859602, Final residual = 0.0002294703, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.0166128, Final residual = 0.0002192773, No Iterations 1
DILUPBiCG: Solving for h, Initial residual = 0.002214545, Final residual = 3.087828e-05, No Iterations 2
Min/max T:358.1999 571.4709
GAMG: Solving for p_rgh, Initial residual = 0.03569226, Final residual = 0.00023627, No Iterations 3
time step continuity errors : sum local = 0.007490534, global = -2.530013e-12, cumulative = -2.741002e-10
Min/max rho:0.9387865 1.497791
DILUPBiCG: Solving for omega, Initial residual = 7.168458e-05, Final residual = 1.611001e-06, No Iterations 1
DILUPBiCG: Solving for k, Initial residual = 0.009050288, Final residual = 0.0002684196, No Iterations 1

Solving for solid region consT
DICPCG: Solving for T, Initial residual = 4.542342e-06, Final residual = 4.466919e-07, No Iterations 1
Min/max T:303.0746 498.7842

Solving for solid region front
DICPCG: Solving for T, Initial residual = 1.738159e-06, Final residual = 1.324394e-07, No Iterations 1
Min/max T:303.6354 437.2578

Solving for solid region back
DICPCG: Solving for T, Initial residual = 1.853885e-06, Final residual = 1.408841e-07, No Iterations 1
Min/max T:303.6258 437.5329
ExecutionTime = 21756.26 s ClockTime = 21760 s

Time = 15000


Solving for fluid region cavityAir
DILUPBiCG: Solving for Ux, Initial residual = 0.01729756, Final residual = 0.0002239076, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.01839812, Final residual = 0.0002220848, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.01681352, Final residual = 0.0002197067, No Iterations 1
DILUPBiCG: Solving for h, Initial residual = 0.002202084, Final residual = 3.018876e-05, No Iterations 2
Min/max T:358.2 571.8507
GAMG: Solving for p_rgh, Initial residual = 0.03509366, Final residual = 0.000223746, No Iterations 3
time step continuity errors : sum local = 0.007095998, global = 4.35557e-12, cumulative = -2.697446e-10
Min/max rho:0.938163 1.497791
DILUPBiCG: Solving for omega, Initial residual = 7.161236e-05, Final residual = 1.56344e-06, No Iterations 1
DILUPBiCG: Solving for k, Initial residual = 0.008882402, Final residual = 0.0002667814, No Iterations 1

Solving for solid region consT
DICPCG: Solving for T, Initial residual = 4.419945e-06, Final residual = 4.319703e-07, No Iterations 1
Min/max T:303.0746 498.7842

Solving for solid region front
DICPCG: Solving for T, Initial residual = 1.717718e-06, Final residual = 1.261334e-07, No Iterations 1
Min/max T:303.6354 437.2588

Solving for solid region back
DICPCG: Solving for T, Initial residual = 1.843119e-06, Final residual = 1.449087e-07, No Iterations 1
Min/max T:303.6258 437.5315
ExecutionTime = 21758.93 s ClockTime = 21763 s

If there is any problem in openFoam 2.1 regarding viewFactor radiation model......??

regards,
baran