- **OpenFOAM Post-Processing**
(*https://www.cfd-online.com/Forums/openfoam-post-processing/*)

- - **Reynolds Stress Tensor**
(*https://www.cfd-online.com/Forums/openfoam-post-processing/87105-reynolds-stress-tensor.html*)

Reynolds Stress TensorHello 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 |

In the controlDict, the last part you can choose to add functions:
Code:
`functions` This function will give a symmetric tensor field with 6 components for the times you choose. |

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 |

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. |

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!!!) |

It finally makes some sense:
Tau= mu*dV/dy stressComponents uses nu [m2 s-1] instead of mu [kg m-1 s-1], and that is the reason why the stress tensor yields [m2 s-2] However I still need to know how to calculate the stress tensor components |

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 :) |

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 |

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 https://www.cfd-online.com/Forums/op...rmal-wall.html) 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 |

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