CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

SimpleFoam k and epsilon bounded

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   November 25, 2008, 10:53
Default Hello everyone. I have been
  #1
New Member
 
Naveed Akram
Join Date: Mar 2009
Posts: 3
Rep Power: 8
nedved is on a distinguished road
Hello everyone.

I have been working on the nlf-0414 laminar airfoil. I have calculated the drag and lift coefficients for various angles and have got decent results. I have been using the steady state solver - simpleFoam - for unstructured grids. My simulations are two-dimensional.

I am now working on an ice accreted nlf-0414 airfoil. I am using the same solver settings as the non-ice nlf-0414 airfoil but my solution blows up after a few iterations. Here are some details about the case:

I created the mesh in ICEMCFD. I converted it into a fluent mesh which i then converted into foam format using fluent3dMeshTofoam.

As the case is 2D, i am using empty boundaries on the left and right sides of the domain. I am using inlet and outlet boundaries and walls for the airfoil, top and bottom regions.

I am using the k-epsilon turbulence model. I estimated k to be 20.23 and epsilon to be 166.12. I used these same settings for the non-ice cases which converged fine. My Reynolds number based on airfoil chord (0.914m) is 4.6x10^6 and inlet velocity is 73.45m/s.

I am attaching my case file.



When i run my case this is the problem i am having:

Create time

Create mesh for time = 0

Reading field p

Reading field U

Reading/calculating face flux field phi

Selecting incompressible transport model Newtonian
Selecting RAS turbulence model kEpsilon
kEpsilonCoeffs
{
Cmu 0.09;
C1 1.44;
C2 1.92;
alphaEps 0.76923;
}


Starting time loop

Time = 1

DILUPBiCG: Solving for Ux, Initial residual = 1, Final residual = 0.0868802, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 1, Final residual = 0.0384705, No Iterations 1
ICE default IO error handler doing an exit(), pid = 25139, errno = 0
DICPCG: Solving for p, Initial residual = 1, Final residual = 0.000974596, No Iterations 453
time step continuity errors : sum local = 0.0443247, global = -0.000256781, cumulative = -0.000256781
DILUPBiCG: Solving for epsilon, Initial residual = 0.177983, Final residual = 0.0134905, No Iterations 1
bounding epsilon, min: -5124.54 max: 2.59707e+06 average: 23725.9
DILUPBiCG: Solving for k, Initial residual = 1, Final residual = 0.0221967, No Iterations 1
ExecutionTime = 75.45 s ClockTime = 77 s

Time = 2

DILUPBiCG: Solving for Ux, Initial residual = 0.00022456, Final residual = 1.72182e-07, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.171213, Final residual = 6.76872e-06, No Iterations 1
DICPCG: Solving for p, Initial residual = 0.199818, Final residual = 0.00173239, No Iterations 1001
time step continuity errors : sum local = 0.25953, global = 0.000524615, cumulative = 0.000267833
DILUPBiCG: Solving for epsilon, Initial residual = 0.380199, Final residual = 3.54249e-13, No Iterations 1
bounding epsilon, min: -62.2232 max: 6.84878e+06 average: 26467.3
DILUPBiCG: Solving for k, Initial residual = 0.00031994, Final residual = 5.93409e-06, No Iterations 1
ExecutionTime = 211.38 s ClockTime = 223 s

Time = 3

DILUPBiCG: Solving for Ux, Initial residual = 0.999831, Final residual = 0.0334756, No Iterations 2
DILUPBiCG: Solving for Uy, Initial residual = 0.999976, Final residual = 0.0290285, No Iterations 2
DICPCG: Solving for p, Initial residual = 0.783759, Final residual = 0.000762911, No Iterations 635
time step continuity errors : sum local = 5126.09, global = -115.949, cumulative = -115.949
DILUPBiCG: Solving for epsilon, Initial residual = 1, Final residual = 0.0740209, No Iterations 2
DILUPBiCG: Solving for k, Initial residual = 1, Final residual = 0.000545361, No Iterations 1
ExecutionTime = 304.56 s ClockTime = 319 s

Time = 4

DILUPBiCG: Solving for Ux, Initial residual = 0.637303, Final residual = 0.0534082, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.392361, Final residual = 0.000317455, No Iterations 2
DICPCG: Solving for p, Initial residual = 0.949414, Final residual = 0.00213447, No Iterations 1001
time step continuity errors : sum local = 4384.93, global = -1118.18, cumulative = -1234.13
DILUPBiCG: Solving for epsilon, Initial residual = 0.255896, Final residual = 0.0139967, No Iterations 1
bounding epsilon, min: -1.31507e+11 max: 2.87675e+27 average: 9.48764e+21
DILUPBiCG: Solving for k, Initial residual = 0.999977, Final residual = 0.092381, No Iterations 1
ExecutionTime = 441.92 s ClockTime = 466 s

Time = 5

DILUPBiCG: Solving for Ux, Initial residual = 0.565411, Final residual = 0.000464199, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.361508, Final residual = 0.000488244, No Iterations 1
DICPCG: Solving for p, Initial residual = 5.22619e-06, Final residual = 1.98698e-08, No Iterations 1
time step continuity errors : sum local = 1.87592e+10, global = -390.727, cumulative = -1624.85
DILUPBiCG: Solving for epsilon, Initial residual = 0.178086, Final residual = 0.0001416, No Iterations 1
bounding epsilon, min: -3.05682e+26 max: 2.8755e+33 average: 5.0373e+27
DILUPBiCG: Solving for k, Initial residual = 0.0246705, Final residual = 0.000480176, No Iterations 1
bounding k, min: -341683 max: 5.29681e+24 average: 2.90027e+19
ExecutionTime = 452.27 s ClockTime = 477 s

Time = 6

DILUPBiCG: Solving for Ux, Initial residual = 0.00134352, Final residual = 1.02079e-05, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.0010846, Final residual = 5.96071e-06, No Iterations 1
DICPCG: Solving for p, Initial residual = 3.86649e-06, Final residual = 8.28192e-08, No Iterations 3
time step continuity errors : sum local = 1.84347e+19, global = 11386.1, cumulative = 9761.24
DILUPBiCG: Solving for epsilon, Initial residual = 2.93311e-10, Final residual = 2.93311e-10, No Iterations 0
DILUPBiCG: Solving for k, Initial residual = 0.114498, Final residual = 0.00215299, No Iterations 1
bounding k, min: -332156 max: 1.09647e+40 average: 8.20484e+34
ExecutionTime = 462.33 s ClockTime = 488 s

Time = 7

DILUPBiCG: Solving for Ux, Initial residual = 0.0498993, Final residual = 0.000172662, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.0784033, Final residual = 0.000290499, No Iterations 1
DICPCG: Solving for p, Initial residual = 2.31156e-23, Final residual = 2.31156e-23, No Iterations 0
time step continuity errors : sum local = 1.52759e+30, global = 1.7678e+14, cumulative = 1.7678e+14
DILUPBiCG: Solving for epsilon, Initial residual = 0.197579, Final residual = 0.00838687, No Iterations 1
bounding epsilon, min: -7.90723e+56 max: 8.65931e+63 average: 4.08564e+58
DILUPBiCG: Solving for k, Initial residual = 0.999368, Final residual = 0.0632189, No Iterations 1
bounding k, min: -4.54562e+29 max: 1.42308e+47 average: 1.79576e+42
ExecutionTime = 471.52 s ClockTime = 500 s

Time = 8

DILUPBiCG: Solving for Ux, Initial residual = 1, Final residual = 7.10734e-08, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.646717, Final residual = 9.62027e-09, No Iterations 1
DICPCG: Solving for p, Initial residual = 4.36332e-21, Final residual = 4.36332e-21, No Iterations 0
time step continuity errors : sum local = 1.27322e+32, global = 8.48049e+15, cumulative = 8.65727e+15
DILUPBiCG: Solving for epsilon, Initial residual = 0.997213, Final residual = 2.00069e-08, No Iterations 1
bounding epsilon, min: -1.51347e+71 max: 1.90819e+89 average: 7.36319e+83
DILUPBiCG: Solving for k, Initial residual = 0.203853, Final residual = 7.00189e-08, No Iterations 1
bounding k, min: -9.21274e+43 max: 3.56366e+57 average: 1.11523e+52
ExecutionTime = 480.72 s ClockTime = 509 s

Time = 9

DILUPBiCG: Solving for Ux, Initial residual = 4.80891e-09, Final residual = 4.80891e-09, No Iterations 0
DILUPBiCG: Solving for Uy, Initial residual = 4.77966e-09, Final residual = 4.77966e-09, No Iterations 0
DICPCG: Solving for p, Initial residual = 1.15667e-20, Final residual = 1.15667e-20, No Iterations 0
time step continuity errors : sum local = 2.88697e+32, global = 1.34591e+17, cumulative = 1.43248e+17
DILUPBiCG: Solving for epsilon, Initial residual = 9.2793e-12, Final residual = 9.2793e-12, No Iterations 0
bounding epsilon, min: 4.97127e-19 max: 1.90819e+89 average: 7.36319e+83
DILUPBiCG: Solving for k, Initial residual = 2.00211e-06, Final residual = 2.97586e-13, No Iterations 1
bounding k, min: -6.9942e+51 max: 1.64917e+75 average: 4.51736e+69
ExecutionTime = 490.87 s ClockTime = 521 s

Time = 10

DILUPBiCG: Solving for Ux, Initial residual = 4.50988e-06, Final residual = 3.0425e-07, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 2.41985e-05, Final residual = 1.47112e-06, No Iterations 1
DICPCG: Solving for p, Initial residual = 3.28653e-20, Final residual = 3.28653e-20, No Iterations 0
time step continuity errors : sum local = 5.24766e+32, global = -6.73284e+15, cumulative = 1.36515e+17
DILUPBiCG: Solving for epsilon, Initial residual = 7.52866e-30, Final residual = 7.52866e-30, No Iterations 0
DILUPBiCG: Solving for k, Initial residual = 3.68813e-06, Final residual = 1.75885e-07, No Iterations 1
bounding k, min: -6.74138e+68 max: 1.08664e+75 average: 2.03979e+70
ExecutionTime = 500.85 s ClockTime = 533 s


K and epsilon keep on being bounded which causes the case to diverge. I have tried to adjust the inlet values of k and epsilon but nothing changes. I have looked through the forum for similar problems but still cannot fix my problem. I would be very greatful for any suggestions to improve my case.

Also, to change from the k-epsilon to spalartallmaras turbulence model, what changes do i have to make in my case?
nedved is offline   Reply With Quote

Old   December 6, 2008, 05:36
Default Dear Naveed even i have faced
  #2
New Member
 
Ameya Durve
Join Date: Mar 2009
Location: Mumbai, Maharashtra, India
Posts: 20
Rep Power: 8
ameya is on a distinguished road
Dear Naveed
even i have faced such a problem.
The only solution i came across was to use hex mesh
ameya is offline   Reply With Quote

Old   December 9, 2008, 22:04
Default hi, I meet the same problem
  #3
Senior Member
 
weihong yao
Join Date: Mar 2009
Posts: 117
Rep Power: 8
ivanyao is on a distinguished road
hi,
I meet the same problem ever, but when i am change the BC,i fix the problem.
you should check your BC again.
ivan
ivanyao is offline   Reply With Quote

Old   December 10, 2008, 04:45
Default dear ivan/yao, what do you
  #4
Member
 
lord_kossity's Avatar
 
Andreas Dietz
Join Date: Mar 2009
Location: Munich
Posts: 79
Rep Power: 8
lord_kossity is on a distinguished road
dear ivan/yao,

what do you change your BC to? And which BC do you modify, only k and eps or also U?

Kind regards,
Andreas
lord_kossity is offline   Reply With Quote

Old   December 11, 2008, 05:27
Default try the komegaSST solver. this
  #5
Senior Member
 
Wolfgang Heydlauff
Join Date: Mar 2009
Location: Germany
Posts: 136
Rep Power: 8
wolle1982 is on a distinguished road
try the komegaSST solver. this works better. the epsilon model calculates freestream vorticities very good. the komegaSST is better used on airfoils where the freestream vorticities are not so important.
wolle1982 is offline   Reply With Quote

Old   April 8, 2010, 11:15
Default
  #6
DLC
Member
 
Davide Lupo Conti
Join Date: Nov 2009
Posts: 34
Rep Power: 7
DLC is on a distinguished road
Hi Foamers,
I know I'm entering the conversation quite late, but i'm having more or less the same problems...

I'm new to simpleFoam, and i'm testing it on a NACA0012. (2D problem)
I use hex mesh generated using a fortran scripts found here (http://www-rocq.inria.fr/macs/spip.php?rubrique69)... i have to say they generate a very nice mesh...

I'm having some issues understanding which turbulence mode I must use...
the best seems to be the k-e with the same values as nedved.
I tested the realizable k-e but the solution never reaches a steady state..
I tried the SST, but the solution blows up after few iterations... can anyone tell me the values for the SST coefficients? I used the ones I used for an interDyMFoam case and in that case they were fine...

which BC are you using? I'm using more or less the same as nedved..

last, and very important thing.... how can i find out forces on the airfoil? someone told me that it was possible while post-processing in paraview, but I couldn't figure out how.. does anyone know? the code doesn't calculate forces anywhere, right?

answers would result quite important for me....
thanks a lot...

DLC
DLC is offline   Reply With Quote

Old   October 25, 2013, 03:30
Exclamation
  #7
New Member
 
Visakh M G
Join Date: Dec 2010
Location: Thiruvananthapuram, India
Posts: 4
Rep Power: 6
visakhmg is on a distinguished road
Has anyone got the solution to this problem yet? About bounding of epsilon values? please help. I am faving the same proble. Thanks in advance.
\vmg
visakhmg is offline   Reply With Quote

Old   October 28, 2013, 05:25
Default
  #8
New Member
 
xingyu SIMA
Join Date: Sep 2013
Posts: 6
Rep Power: 3
sima_op is on a distinguished road
hallo, i'm facing this probleme,too. need for help.
sima_op is offline   Reply With Quote

Old   October 28, 2013, 05:56
Default
  #9
Senior Member
 
Nima Sam
Join Date: Sep 2009
Location: Tehran, Iran
Posts: 1,123
Blog Entries: 1
Rep Power: 14
nimasam is on a distinguished road
Send a message via Yahoo to nimasam
first try to reach steady-state solution in laminar condition, then turn on turbulence
__________________
Training Course on OpenFOAM at (http://www.isme.ir/)
My Weblog (http://openfoam.blogfa.com/)
nimasam is offline   Reply With Quote

Old   October 28, 2013, 06:39
Default
  #10
New Member
 
xingyu SIMA
Join Date: Sep 2013
Posts: 6
Rep Power: 3
sima_op is on a distinguished road
yes, thank you very much for your reply.
in fact, i have tried to off the turbulence in RASProperties,and it works very well. But if i turn on turbulence after 400 iterations(i'm not sure when it will reach the steady-state), there will be the same wrong message.
sima_op is offline   Reply With Quote

Old   October 29, 2013, 04:27
Default
  #11
New Member
 
Visakh M G
Join Date: Dec 2010
Location: Thiruvananthapuram, India
Posts: 4
Rep Power: 6
visakhmg is on a distinguished road
@nimasam; thankyou.
Yeah, i had tried with running laminar for some time and switching on turbulence later (at once). Still it has got the same problem of unbounding epsilon (it shows "bounding epsilon, min: -0.000470716658863 max: 454112.158676 average: 133.216441665"). The geometry is little heavy, with porous media and i have noticed unbounding of epsilon happens even if i give bounding limits. Is it like it bounds the value of epsilon after printing? The velocity and pressure fields are comparable to fluent results though, but i am not satisfied. Can you tell me which is the best option:
running pottentialFoam to get inviscid flow pattern followed by porousSimpleFoam; or running laminar followed by switching turbulence at once; or still gradually increasing the turbulence intensity? Or is it the boundary conditions and initial conditions of k and epsilon? Thanks in advance..
\vmg
visakhmg is offline   Reply With Quote

Old   October 29, 2013, 04:54
Default
  #12
Senior Member
 
Nima Sam
Join Date: Sep 2009
Location: Tehran, Iran
Posts: 1,123
Blog Entries: 1
Rep Power: 14
nimasam is on a distinguished road
Send a message via Yahoo to nimasam
well, all options are on the table

running potentialFlow in the begining of simulation will reduce the time of reaching steady-state, if you face sever condition then you may want to turn off turbulence and give a laminar result which can be an initial for lateral turbulence modeling.
if you still face the difficulty you may want to:
1- check your BC
2-check your fvScheme
3- use relaxation in fvSolution
__________________
Training Course on OpenFOAM at (http://www.isme.ir/)
My Weblog (http://openfoam.blogfa.com/)
nimasam is offline   Reply With Quote

Old   October 29, 2013, 06:19
Default
  #13
New Member
 
xingyu SIMA
Join Date: Sep 2013
Posts: 6
Rep Power: 3
sima_op is on a distinguished road
hallo, thanks very much for your reply to this question, my simulation was converge after i made changes in FvScheme, i changed the 'gausse linear' to 'bounded Gauss upwind' for div(phi,U)div(phi,k)div(phi,k)and div(phi,epsilon), i hope these can help you a litte,too.
However, in fact, i still don't understand why i should changes them....it will be very kind if anyone can explaine that for me..
sima_op is offline   Reply With Quote

Old   November 4, 2013, 15:13
Default
  #14
New Member
 
Karthik Rudra Reddy
Join Date: Nov 2013
Posts: 6
Rep Power: 3
kreddy is on a distinguished road
Quote:
Originally Posted by sima_op View Post
hallo, thanks very much for your reply to this question, my simulation was converge after i made changes in FvScheme, i changed the 'gausse linear' to 'bounded Gauss upwind' for div(phi,U)div(phi,k)div(phi,k)and div(phi,epsilon), i hope these can help you a litte,too.
However, in fact, i still don't understand why i should changes them....it will be very kind if anyone can explaine that for me..
In general, upwind schemes tend to suppress numerical oscillations and would be more stable than linear schemes.
This means that they also tend to suppress the turbulent fluctuations. So if you are only interested in computing the mean flow (and hence using a RANS model like k-epsilon), then upwind schemes are a good option. For cases where you want to capture the unsteady flow (say, in LES) you will have to use linear schemes.
kreddy is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Bounded scheme gives unbounded solution su_junwei OpenFOAM Running, Solving & CFD 3 November 18, 2011 03:35
SimpleFoam k and epsilon bounded nedved OpenFOAM Running, Solving & CFD 1 November 25, 2008 21:21
Bounded slice in Tecplot possible? Sam Tecplot 1 August 20, 2008 12:18
Mesh in wall bounded flow krishh FLUENT 1 December 3, 2007 02:09
Calculation of bounded scalars ankgupta8um OpenFOAM Running, Solving & CFD 1 June 19, 2006 05:03


All times are GMT -4. The time now is 19:01.