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August 14, 2008, 23:49 
Hi forum...
I was trying t

#1 
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Nishant
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Hi forum...
I was trying to get the postchannel plots for the channel395 case in OF1.5. Unfortunately postChannel utility has not been able to generate the Uf.xy, u.xy etc etc plots in OF1.5. I noticed that instead of Umean, now OF1.5 writes UMean (capital M) in every time directory. Also R file is not present in time directory. Is this error in postChannel utility because of that? I go through both the codes and find no difference. I am still looking into it but It will be helpful if someone can tell me fast. regards, Nishant
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Thanks and regards, Nishant 

August 20, 2008, 22:14 
can anyone take out some time

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Nishant
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can anyone take out some time to comment on the above problem. I changed the postchannel utility with UMean instead of Umean.. and now the utility is complaining about R file not found.
Now the question is, why channeloodle utility is not writting R field??
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Thanks and regards, Nishant 

May 5, 2009, 05:27 

#3 
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Leonardo Giampani Morita
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Hello,
I have the same problem...after running the postChannel utility, no files are created...has somebody figured out what the cause of the problem is? Thanks, Leonardo 

May 6, 2009, 20:48 

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Daniel WEI (老魏)
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June 8, 2009, 04:44 

#5 
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Dr. Fabian Schlegel
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UPrime2Mean is not R I guess. Nevertheless you have to use UPrime2Mean to calculate the reynolds stresses.


June 8, 2009, 04:49 

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Daniel WEI (老魏)
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Then, their differences are???
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June 8, 2009, 05:29 

#7 
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Dr. Fabian Schlegel
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Allright I think the following, but this is just an assumption, not proved up to now:
R = average(u'_i u'_j) UprimeToMean = average(u_i u_j) An by this R becomes: R = average ( u'_i u'_j) = average(u_i u_j)  average(u_i) * average (u_j) (1) Edit: I found a working postChannel in the GIT repository. But I am still 99% sure, that R is not the same als Uprime2Mean, if R is the reynolds stress tensor. But I am not able to figure out where the calculation (see equation 1) is done so far. But I am not so familiar with C++, so it is a bit difficult for me to understand the source code :/ Please correct me if I am wrong. Last edited by fs82; June 8, 2009 at 10:34. Reason: new awarenesses 

June 9, 2009, 05:32 

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Dr. Fabian Schlegel
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Mea culpa :/ I went into the fieldAverage routines and checked the calculation of the reynolds stresses and I have to take back everything and state the opposite. OpenFoam calculates average(u_i u_j) but writes out everytime step average(u'_i u'_j). This is done by equation (1). But before calculation the new reynolds stress tensor equation (1) is used again to get average(u_i u_j) from average(u'_i u'_j). So everything is fine and you can use UPrimeToMean instead of R from former OpenFoam versions.
Sry, fs82 

June 9, 2009, 05:43 

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December 9, 2011, 14:11 
FieldAveragingReynolds stress

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pooyan
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Hey guys,
I am trying to get Reynolds Stress Components for Lid driven cavity flow. By using fieldaveraging, I get 6 components for uprime2mean as written below UPrime2Mean:0 UPrime2Mean:1 UPrime2Mean:2 UPrime2Mean:3 UPrime2Mean:4 UPrime2Mean:5 My questions are that, are these components the Reynolds Stress tensor?! Which of these representing <uu>, <uv>, <vv> and etc?! Thanks 

December 11, 2011, 07:37 

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December 12, 2011, 15:36 

#12 
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pooyan
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Thanks. I went through this website, but I could not get any help from that. Do you think these six components are Reynolds Stress tensor?!
I guess Uprime2Mean (0) is <uu> and Uprime2Mean (1) is <vv> 

December 13, 2011, 05:26 

#13 
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Dr. Fabian Schlegel
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Alright, the site I suggested wasn't the best one to read. The best way is to try it out. I guess you have performed a test run and already have the field "UPrime2Mean". So do the following: "foamCalc components UPrime2Mean" in your foam case directory. This will provide you each component uu, vv, ww, uv, uw, vw in a separate file. Compare the values of your original symmTensor field to the ones in the files and you have the answer.
For my understanding UPrime2Mean represents more or less the Reynolds stresses. If you perform an LES you have: Mean Value + Fluctuations + Subgrid stresses = Instantaneous value and UPrime2Mean include for my understanding only the Fluctuations. In case of RANS I am not sure, but I think UPrime2Mean does not exist there (never tried a RANS), but you got an additional field named R, which represents the Reynolds stresses. May be one of the more advanced user could give you more information. kind regards, Fabian 

December 13, 2011, 17:58 

#14 
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pooyan
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Thanks for your complete response. I do appreciate your help.
I will try those suggested ways. Best Wishes, 

January 17, 2012, 17:39 

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pooyan
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Fabian,
I tried to get access to the source code to check the calculation of UPrime2Mean. I went through fieldAverage.C and fieldAverage.H, but unfortunately I could not see the calculation of Uprime2Mean in those files. Where should I check that out? Thanks, Quote:


January 18, 2012, 06:26 

#16 
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Dr. Fabian Schlegel
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You have to go to the follwing directory: <foampath>/OpenFOAM1.6.x/src/postProcessing/functionObjects/field/fieldAverage/fieldAverage and everything is there. The calculation of the mean and Prime2Mean values could be found in fieldAverageTemplates.C after a quick look.
hope this helps, Fabian 

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