Can RMS velocity even be smaller than mean velocity?

lgas222 · May 22, 2012, 22:57

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.

Far · May 23, 2012, 01:17

It can be. RMS is the root mean square of fluctuating components that is u',v' and w'.

lgas222 · May 23, 2012, 04:18

Quote:

Originally Posted by Far

It can be. RMS is the root mean square of fluctuating components that is u',v' and w'.

Thanks for your reply.

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

Far · May 23, 2012, 04:26

I guess so.

Far · May 23, 2012, 04:36

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

May 22, 2012, 22:57	Can RMS velocity even be smaller than mean velocity?	#1
lgas222 New Member linlong Join Date: Feb 2012 Posts: 4 Rep Power: 14	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
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	It can be. RMS is the root mean square of fluctuating components that is u',v' and w'. jzc likes this.

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May 23, 2012, 04:26		#4
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	I guess so.

May 23, 2012, 04:36		#5
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	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