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March 5, 2013, 04:58 
Initial Residual for p too high!

#1 
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Nikesh Bhattarai
Join Date: Nov 2011
Location: Sacheon, South Korea
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Hi all,
I am simulating a simple 2D flat plate flow in OpenFoam using simpleFOAM to validate a new turbulence model that I would like to implement here. This new turbulence model is a slight modification of the kOmegaSST model which includes few new terms into the nut equation. Results from kOmegaSST model are all OK! However, when I use this new model for the same grid, my initial pressure residuals oscillate around a pretty high value, at around 0.03 while the initial U,k and omega residuals are all at a reasonable convergence criterion, at around 10^5. This is not making much sense to me. Because, after some iterations(about 6~7,000) when I extract the results (even without reaching the convergence tolerance) and compare, they don't yet seem so weird or deviating highly from that of the SST's results. I have checked my code numerous times, doesn't seem to have any problems in there. Could there be a problem with the solvers I chose? I am as well wondering how the presidual is calculated in simpleFOAM. I would highly appreciate any insights into this! Thanks! Nikesh These are my settings and I've used the same for kOmegaSST (in the pic attached). 

March 5, 2013, 05:17 

#2 
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Ehsan
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hi
Test for one or two order lower p tolernces than U,... 1e9 or 1e10 

March 5, 2013, 06:23 

#3 
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Nikesh Bhattarai
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Thanks!
Tried, yet not much of a difference. 

March 9, 2013, 16:51 

#4 
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AndreiCFD
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Hi
Basically I am having the same problem.... I just want to ask you if you managed to do it in the end. I am simulating the flow over an aerofoil using k omega sst and simpleFoam with wall functions.......... Have you got any ideas? Thanks Andrei 

March 10, 2013, 01:35 

#5 
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Nikesh Bhattarai
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Hii Andrei,
Well, I am still stuck with the same problem. Obviously higher presidual means mass is not being conserved so well somewhere in the cells. You might want to look into your boundary conditions once more. Basically that is what I am trying to do too. And the schemes and type of mesh you are using for airfoil flow. 

March 10, 2013, 07:28 

#6 
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AndreiCFD
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Hi
Ok I understand . I am using k omega sst , wall functions and simpleFoam solver ..... I have changed my boundary conditions many times still nothing......for example how you o file looks like and something that I don't understand : how do you calculate the turbulent kinetic energy K and the rate of dissipation W(omega)....... thanks Andrei 

March 10, 2013, 10:56 

#7 
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Daniel P. Combest
Join Date: Mar 2009
Location: St. Louis, USA
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Nick,
There are some strategies that I would try to get these residuals down to something you would like.
There are a lot of other strategies that you can try, but this one might be sufficient. Without knowing more details like divergence schemes; mesh structure and checkmesh results; y+ values; and boundary conditions there is not much to add on my part. I would look at the thread http://www.cfdonline.com/Forums/ope...problems.html and then move on to a search of the forum. There are many threads about simpleFoam convergence...but my list of threads is not in front of me right now. good luck. Last edited by chegdan; March 10, 2013 at 19:01. Reason: spelling 

March 15, 2013, 05:17 

#8 
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Ehsan
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how can decrease the initial residuals for p in unsteady problems when relaxations are not applicable?


May 25, 2017, 02:52 

#9 
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Thodoris
Join Date: Apr 2016
Location: Greece
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Hello guys,
I am running a simulation of a flow over two wings. My simulation is 3d.I check the mesh and there is no error. I am using freestream bc and wall functions. Solver is simplefoam and turbulence model spalart almaras dudes. The problem is when I ran with coarse mesh the solution converge but when I ran with finer mesh the pressure residuals don't fall under 10^5 they stop at about 2*10^4.I used snappyhexmesh for the mesh. Any advice would be useful thank you in advance. Thodoris 

May 25, 2017, 03:58 

#10  
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AndreiCFD
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Quote:


May 25, 2017, 17:40 

#11 
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Thodoris
Join Date: Apr 2016
Location: Greece
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Andrei,
Thank you a lot for your answer.I am trying to calculate the cl, cd but i am having troubles because of my geometry, which consists two wings in the same but opposite angle of attack (+ 8 degrees) so i am having problems with the normals. I hope you have an idea to face this problem.I am attaching my geometry. Thank you very much in advance. 

May 26, 2017, 06:53 

#12  
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AndreiCFD
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Quote:
Cheers 

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