
[Sponsors] 
April 11, 2011, 12:42 
Reynolds Stress Tensor

#1 
New Member
Sergio
Join Date: Apr 2011
Posts: 8
Rep Power: 8 
Hello Foamers
I am quite new to CFD and OpenFoam, and I was wondering if someone can help me with this: How can be calculated / displayed the Reynolds Stress Tensor, in order to, say, calculate the stresses at a given point of the domain. Please also note that I am using a LES turbulence model Thanks in advance for your help 

April 11, 2011, 13:29 

#2 
Member
David Aljure
Join Date: Mar 2011
Location: CTTC Universidad Politécnica de Catalunya. Spain
Posts: 38
Rep Power: 8 
In the controlDict, the last part you can choose to add functions:
Code:
functions { fieldAverage1 { type fieldAverage; functionObjectLibs ( "libfieldFunctionObjects.so" ); enabled true; outputControl timeStep; outputInterval 100; fields ( U { mean on; prime2Mean on; base time; } p { mean on; prime2Mean off; base time; } ); } } This function will give a symmetric tensor field with 6 components for the times you choose. 

April 12, 2011, 10:42 

#3 
New Member
Sergio
Join Date: Apr 2011
Posts: 8
Rep Power: 8 
Hi David, thanks for your answer. I will try it.
On the other hand, checking commands, I found stressComponents and typed it. The thing, is that it created at each time step a sigmaxx, sigma xy.... sigmazz files. However when I opened any of those files the units I found are [0 2 2 0 0 0 0], while I was expecting [1 1 2 0 0 0 0]. Do you, or any other foamer have something to say about this? Thanks 

April 12, 2011, 12:55 

#4 
Member
David Aljure
Join Date: Mar 2011
Location: CTTC Universidad Politécnica de Catalunya. Spain
Posts: 38
Rep Power: 8 
In its source code, stressComponents is defined as:
laminarTransport.nu()*2*dev(symm(fvc::grad(U))) so I guess its the deviatoric stress tensor divided by the density, hence the units [0 2 2 ...] These stress components are different than the Reynolds stresses: Re Stresses: velocity fluctuation. Dev. Stresses: deformation. 

April 12, 2011, 14:01 

#5 
New Member
Sergio
Join Date: Apr 2011
Posts: 8
Rep Power: 8 
Gracias David
The tech support folks from OpenFoam, have said the following about this issue stressComponents was written for incompressible laminar flow. For LES you need to accumulate the Reynolds stress by averaging during the run.It looks as if it is time for this newbie to dig into the programming aspects of OpenFoam (auch!!!) 

April 12, 2011, 14:20 

#6 
New Member
Sergio
Join Date: Apr 2011
Posts: 8
Rep Power: 8 
It finally makes some sense:
Tau= mu*dV/dy stressComponents uses nu [m2 s1] instead of mu [kg m1 s1], and that is the reason why the stress tensor yields [m2 s2] However I still need to know how to calculate the stress tensor components 

April 13, 2011, 03:23 

#7 
Member
David Aljure
Join Date: Mar 2011
Location: CTTC Universidad Politécnica de Catalunya. Spain
Posts: 38
Rep Power: 8 
If you need to calculate the Re stress tensor use the info in my first post, at the end of control dict add the fieldaveraging function, UPrime2mean gives the Re stress tensor.
I'm also a newbie at foam and programing, but I have digged several times into the source codes. Have fun 

April 18, 2014, 07:30 

#8 
Member
Tony
Join Date: Nov 2013
Posts: 35
Rep Power: 5 
Hi David,
I saw you post about the Reynolds stress tensor. I also found that UPrime2mean yielded six columns which should be stress tensor. I was just wondering how I can get the RMS value from the UPrime2mean file. Hope you can give me some hints. Thank you very much. Kind regards, Tony 

January 4, 2017, 11:06 

#9 
New Member
DimitriF
Join Date: Dec 2016
Location: London
Posts: 19
Rep Power: 2 
Hey David,
This is quite an old post but maybe I'm lucky and get a reply. I want to plot the Reynolds stress versus the normal wall direction at a specific point. To do so, I used the post process utilities of OpenFOAM (simpleFoam postProcess func R latestTime) but I cannot sample this tensor along a line. (see my post here Sample of Reynolds Stress Normal to Wall) I thought I can use your option which is to write the UPrime2Mean using your proposed function above. However, comparing the Reynold stress that I got from the post process utility and UPrime2Mean, there is quite a difference. Any idea why? Cheers, Dimitri 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
postprocessing utility R, calculating Reynolds stress tensor  volker  OpenFOAM PostProcessing  11  January 17, 2016 09:28 
New implemented algebraic Reynolds stress model  volker  OpenFOAM  13  October 21, 2013 00:01 
Reynolds Stress Models  Jade M  Main CFD Forum  0  April 21, 2010 16:38 
Reynolds Stress Boundary Conditions  tstorm  FLUENT  0  July 27, 2009 14:44 
Questions about the Reynolds stress model  empirer2002  Main CFD Forum  1  January 5, 2006 08:37 