CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

fieldAverage meaning in steady state solution

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes
  • 1 Post By HPE

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 17, 2021, 19:48
Question fieldAverage meaning in steady state solution
  #1
New Member
 
Geovany López
Join Date: Sep 2020
Posts: 2
Rep Power: 0
Geovany is on a distinguished road
Hi everyone,

I'm currently working with a 3D cavity-based geometry using rhoSimpleFoam solver. I'd like to get the u_rms value of my simulations. I've already done my simulation in a 5M mesh and I've validated my results.

Reading another thread I know that I have to re-run my simulation and use fieldAverage function object to get UPrime2Mean and then u_rms,x=sqrt(UPrime2Meanxx) using calculator in paraview.

My question is: In a steady simulations, 'cause I used a steady solver, the answer of u_rms,x that I will get is correct? Or it is just averaging through every iteration and this is not useful, since the solution has not yet converged until the last iteration?
In case that the approach of using fieldAverage isn't correct, someone can tell me how I could get the u_rms using a steady solver?

Thanks in advance!
Geovany is offline   Reply With Quote

Old   February 18, 2021, 15:53
Default
  #2
HPE
Senior Member
 
HPE's Avatar
 
Herpes Free Engineer
Join Date: Sep 2019
Location: The Home Under The Ground with the Lost Boys
Posts: 854
Rep Power: 9
HPE is on a distinguished road
No, don't think you can use `fieldAverage` on steady simulations. There can't be any `UPrime2Mean` because there is no `UPrime` (i.e. fluctuating part) for steady simulations.

The object you are looking for is `R` for steady cases. You can use turbulenceFields function object to calculate it, and I don't think you need to rerun your completed RANS simulation. Postprocessing the simulation should be enough.
Geovany likes this.
HPE is offline   Reply With Quote

Old   February 19, 2021, 20:39
Post
  #3
New Member
 
Geovany López
Join Date: Sep 2020
Posts: 2
Rep Power: 0
Geovany is on a distinguished road
Thank you very much for your help.

I used the function that you mentioned and then I was able to plot the turbulence properties in Matlab. But I have another question, I hope that you could help me. How can I compute u'_rms from the Reynolds Stress Tensor?
u'_{rms}=\sqrt{Rxx}
or
u'_{rms}=\sqrt{\frac{1}{3}(Rxx+Ryy+Rzz)}

I think that in the latter option it is assuming that the velocity fluctuations are equal to \sqrt{\frac{2}{3}(k)} and that only applies to isotropic turbulence, right? Or am I mixing basic concepts?

My goal is to plot cross-stream profiles of turbulent fluctations \frac{u'_{rms}}{U_{max}}
Geovany is offline   Reply With Quote

Reply

Tags
fieldaverage, rms velocity, steady state rans

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
The difference between steady state and transient JuPa CFX 36 December 9, 2019 22:50
Simulation time for steady state solution using transient solver spelletier Main CFD Forum 1 June 26, 2019 04:08
mass flow in is not equal to mass flow out saii CFX 12 March 19, 2018 05:21
Steady state solution as an initial condition for a transient problem adnanakhtar FLUENT 7 November 25, 2016 05:16
About the difference between steady and unsteady problems Lisa Main CFD Forum 11 July 5, 2000 14:37


All times are GMT -4. The time now is 15:22.