[gu1]

Hi,

I am using OpenFOAM v11 for a multiphase study (Euler-Euler - LES(NicenoKeqn)) and I am having trouble post-processing the wallShearStress information, even though I know that this version allows the use of the function.

I try

foamPostProcess -func "wallShearStress(phase=water)"
foamPostProcess -func "wallShearStress(U.water)"
foamPostProcess -field U.water -func wallShearStress
foamPostProcess -solver multiphaseEuler -func wallShearStress

All the above functions return me:

Unable to find turbulence model in the database

What am I doing wrong?

[AtoHM]

It does not work in postProcess for multiphaseEuler, I tried it as well. Add it as a function object inside the functions { } section in controlDict and write it out during runtime. E.g. add it to controlDict and run again for 1 more time step.

[Severus]

Hello,
Have you checked this page: https://doc.cfd.direct/openfoam/user...processing-cli
Check the last few lines - they describe the error you got. Maybe this can help you resolve the issue.

I have not tried this specific functionObject, but in the past for multiphaseEulerFoam, the phaseForces function object gave me a similar error. And then I was looking at the code and then I came to know that it would not work with the foamPostProcess utility but rather, we have to add it in the controlDict and compute it during the simulation. Similar to what AtoHM has mentioned.

However, I would like to point out that in the phaseForces.H file, they have explicitly mentioned this.
https://cpp.openfoam.org/v12/phaseForces_8H_source.html

Note that it works only in run-time processing mode and in combination with the multiphaseEuler solver module.

But I dont see them mention anything like this for the wallShearStress functionObject. So, check out the first link and see if that helps.

Thanks

[gu1]

Perfect,

I will add the function to the controlDict and run it for a single timeStep. I believe there will be no loss in the results obtained.

Thanks a lot.

[gu1]

Hi,


I tried, but unfortunately, it keeps notifying that the turbulence model is not valid. I will try other turbulence models, even though it is very uncomfortable.

[gu1]

Hi,


I figured out what was going on. The wallShearStress.H file says that determining the PHASE is not a requirement. That's not true, you have to determine the phase, only then will it work.

[gu1]

Hi,

I was thinking, to get a 'good' result, I have to get the average value, the value at the last instant of time, it doesn't give me much information about the history of the wall shear stress. In that case there's not much I can do, or is there?

[Severus]

Hello,
It depends on what you want. If you want the time-averaged wall shear stress, you should average it over time and not just use the last time step. Or you should calculate it only at the last time step but by using UMean instead of U.

Check out these forums regarding this:
Visualing Time Avergaed Wall Shear Stress
wallGradU or wallShearStress on Time-Averaged Velocity Field

If you have a statistically steady flow, then time-averaging would make sense. For e.g. like a fully developed channel flow or in cases where you expect a quasi-steady behavior of the flow after running the simulation for a long time.

Thanks

[gu1]

Exactly,

It doesn't make sense to do it in the last timeStep. In fact, even if I have, for example, 10 folders in my directory related to the case I'm studying, it wouldn't give a good average result (at least that's what I believe).

[gu1]

Originally Posted by Severus

Hello,
It depends on what you want. If you want the time-averaged wall shear stress, you should average it over time and not just use the last time step. Or you should calculate it only at the last time step but by using UMean instead of U.

Check out these forums regarding this:
Visualing Time Avergaed Wall Shear Stress
wallGradU or wallShearStress on Time-Averaged Velocity Field

If you have a statistically steady flow, then time-averaging would make sense. For e.g. like a fully developed channel flow or in cases where you expect a quasi-steady behavior of the flow after running the simulation for a long time.

Thanks

Hello,

It worked by converting UMean.phase to U.phase and calculating the wallShearStress in the last timeStep, however, there was a slight difference in the result compared to doing it the conventional way, using filedAverange. I don't understand why.

[Severus]

Hello,
I think when you simply change UMean to U at the final time step and then compute the wallShearStress, you don't account for change in nut field over time. This may affect your result if you use wall functions. If you resolve the wall fully, then it shouldn't matter and in that case you should get the same result. So, when you don't resolve the wall, using the fieldAverage value of wallShearStress should be more accurate.

Thanks

[gu1]

Originally Posted by Severus

Hello,
I think when you simply change UMean to U at the final time step and then compute the wallShearStress, you don't account for change in nut field over time. This may affect your result if you use wall functions. If you resolve the wall fully, then it shouldn't matter and in that case you should get the same result. So, when you don't resolve the wall, using the fieldAverage value of wallShearStress should be more accurate.

Thanks

It makes sense.
I managed to write the function for the version I'm using, however, nothing happens (wallShearStress function - OpenFOAM 9 - Error). I did it with the intention of getting around this problem, especially because I need the RMS values ​​and I can't get them the way it was mentioned, by changing the file names.

If you can help me...
Thank you.