CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

About rmse velocity and rms velocity

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

Like Tree6Likes
  • 1 Post By starz
  • 5 Post By LuckyTran

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 9, 2019, 06:02
Post About rmse velocity and rms velocity
  #1
New Member
 
zx
Join Date: Jan 2017
Posts: 4
Rep Power: 5
starz is on a distinguished road
In the Fluent, we can plot the contour of RMSE velocity magnitude (not only velocity but also for other parameters) base on the sampled LES results. However, as I checked, RMSE and RMS are two different concepts.

RMSE is short for root mean square error, which is defined as:http://statweb.stanford.edu/~susan/c...it/node60.html
It is the root mean square of the instantaneous velocity subtract by the average velocity.

RMS is not an error. It is the root mean square of the instantaneous velocity without subtracting anything.

I checked the ANSYS Fluent Theory Guide. I only find RMS in instead of RMSE. And in our Forum, people are mostly talked about RMS.
Therefore, I am confused. Is RMSE in Fluent is the root mean square error of velocity or root mean square of velocity?

Thanks
Best regards
StarZ
soheil_r7 likes this.
starz is offline   Reply With Quote

Old   April 9, 2019, 17:14
Default
  #2
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 4,013
Rep Power: 48
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
This question has been asked over and over and over again.

As you state correctly, RMS is root mean square of instantaneous velocity without subtracting anything. RMSE is the root mean square error, which is equivalent to the RMS of the fluctuating velocity.

For unsteady flows, it was presumed obvious that we are looking for RMS of fluctuating velocities. But then one day people realized that RMS of velocity is confusing. So Fluent changed the labeling from RMS to RMSE to make it clearer that it is calculating RMSE. Fluent has always calculated RMSE, but you will find it labeled RMS in the program or manual.

For turbulent flows people are talking about the RMS of the fluctuating velocity (rms of u', v', or w'), which is the RMSE of the instantaneous velocity. A lot of people say RMS when they actually mean RMSE. Heck a lot of people call u',v', w' as "the rms velocity."
soheil_r7, roi247, starz and 2 others like this.
LuckyTran is offline   Reply With Quote

Reply

Tags
definition, rms velocity, rmse, unsteady flow

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
RMS Velocity values Firefly STAR-CCM+ 0 April 26, 2016 13:29
Prob in rms velocity components, pls help.. sakurabogoda CFX 5 February 13, 2013 21:30
Can RMS velocity even be smaller than mean velocity? lgas222 FLUENT 4 May 23, 2012 04:36
RMS velocity in Cylindrical coordinates ? lcw FLUENT 2 October 5, 2006 04:49
RMS velocity coordinates transform ??? lcw FLUENT 0 February 22, 2006 22:29


All times are GMT -4. The time now is 04:35.