# Can RMS velocity even be smaller than mean velocity?

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 May 22, 2012, 22:57 Can RMS velocity even be smaller than mean velocity? #1 New Member   linlong Join Date: Feb 2012 Posts: 4 Rep Power: 13 Dear all, I'm using the mixture, k-e, air-water two phases model in FLUENT to simulate bubble column. I calculated with transient mode. After calculation, I checked the results: RMS velocity magnitude and mean velocity magnitude. I found out that RMS value is even smaller than mean value. Does anyone know how can it be like this? Is there anything wrong? Thanks a lot.

 May 23, 2012, 01:17 #2 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,552 Blog Entries: 6 Rep Power: 53 It can be. RMS is the root mean square of fluctuating components that is u',v' and w'. jzc likes this.

May 23, 2012, 04:18
#3
New Member

linlong
Join Date: Feb 2012
Posts: 4
Rep Power: 13
Quote:
 Originally Posted by Far It can be. RMS is the root mean square of fluctuating components that is u',v' and w'.

I have one more question: is RMS calculated as ((x1^2+x2^2+x3^2+...+xn^2)/n)^0.5?

 May 23, 2012, 04:26 #4 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,552 Blog Entries: 6 Rep Power: 53 I guess so.

 May 23, 2012, 04:36 #5 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,552 Blog Entries: 6 Rep Power: 53 Some links are shared here, where you can find the discussion about the RMS velocity http://www.cfd-online.com/Forums/flu...ity-ratio.html

 Tags air-water, fluent, k-e, rms