Hi, can anyone please tell me how to extract Reynolds stress as an outcome from a simulation? I'm validating an experiment and couldn't figure out how to extract it. I'm using RANS K-epsilon and K-Omega SST turbulence models

This is a job for the ``turbulenceFields`` function object

this is .com branch, but the same function exists in .org branch if this is what you are using. You might just want to check the documentation related to your version to make sure you use the proper syntax

Thank you for this, I understand it is a function object, but I'm not familiar with .org and .com branch, if you don't mind can you please explain what it is? I'm using OpenFOAM v2406

I'll take a look at this now and update you

OpenFOAM-v2406 is the OpenCFD branch (openfoam.com)

My link is the right one for you

The other development branch is the OpenFOAM foundation branch (openfoam.org), currently at OpenFOAM-12

Ohh okay, that's new for me to know that there are 2 versions. It seems like I'm working on .com branch

yep, you do!

Actually there is a 3rd branch... But I might summon the mighty hardcore users if I say it aloud 😱

Ohh, is that so😅. I better take baby steps

Is outputing "R" a space consuming thing? I had like 50 GB of space and my simulation ran only for 50 iterations and my machine went out of storage. without that, it would take only upto 20 GB of space for 500 iterations. or am I missing something?

One R value has 6 scalar variables in it.

yep, R is pretty big as qr said

You might want to reduce the amount of data you write to disk by either changing the write intervals, or use purgeWrite to remove older iterations since you are doing RANS

Ohh shoot🙃

I understood the first part of changing write intervals. However, I'm not aware of purgeWrite. can you please tell me what it is exactly?

It's a parameter in controlDict to remove older iterations data after writing new one

for instance setting ``purgeWrite 2;`` will save only 2 iterations saved to disk. Each time a new one is saved, the oldest one is removed

Ohh okay, if I run the simulation for 500 iterations, then as you mentioned if

purgeWrite 2

then the final outputs will be the data of 499 and the 500th iteration. Am I correct?

yep

Ohh that's nice. Thank you very much for the explanation

I calculated 'R' using the turbulence fields object and now I want to plot the

Reynold's shear stress

. Can you please tell me how to do that? When I searched it in google it showed something called

UPrime2mean

and we have to use it to estimate it and I don't understand how it works

Is

UPrime2mean

an another function object?

yep, you can compute it with the ``fieldAverage`` function object

Ohh okay, found it. Thanks. will it calculate the Reynolds shear stress directly or do we need to do something else in the process

When I estimated both

UPrime2Mean and Reynolds Stress Tensor 'R'

using FOs, Paraview automatically provided the reynold's shear stress at respective planes https://cdn.discordapp.com/attachments/598785402391887872/1362400786994303088/image.png?ex=6802421b&is=6800f09b&hm=71b0fd7e4b3d778344a307b8ae2ed4f0fcdddbad648ca875171544c8e2f70759&