CFD Online Logo CFD Online URL
Home > Forums > CFX

different between the various averaging

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

LinkBack Thread Tools Display Modes
Old   June 8, 2001, 09:51
Default different between the various averaging
Posts: n/a
Hi, Is there anyone can tell me the difference between the mass averaging, area averaging, theta_averaing, I mean the physical meaning.

I am runing a case of centrifugal pump, and want to get the velocity and pressure average value in some special regions, but I do not understand the physical meaning of these three averaging methods.

  Reply With Quote

Old   June 8, 2001, 13:52
Default Re: different between the various averaging
Jan Rusås
Posts: n/a
Dear Huewei,

I will try to explain my answer by an example.

consider this very simple case:

2 face's

face 1 face 2 area A 1 2 massflow m 1 1 x variable 1 0.5

area average = (A1*x1+A2*x2)/(A1+A2)= (1*1+2*0.5)/(1+2)= 2/3

mass average = (m1*x1+m2*x2)/(m1+m2)= (1*1+1*0.5)/(1+1)= 3/4

When calculating a pressure difference (both static and dynamic) you must use the mass average - it comes from the energy equation.

For averaging the velocity the area average should be ok.

Regards Jan
  Reply With Quote

Old   June 18, 2001, 23:41
Default Re: different between the various averaging
Robin Steed
Posts: n/a
A mass average is calculating by taking the mass-integral of the scalar and dividing by the total mass-flow. Area averaged quantities are calculated by taking the area-integral and dividing by the total area. Theta averaged quantities are taken by integrating over the entire angular extent and dividing by the total angle (typically used by averaging along lines of constant radii to estimating mixed-out quantities for a downstream component).

Whether to use mass averaging or area averaging depends on how a quantity is conserved.

i) If you are concerned with a conserved quantity, such as momentum or total pressure, a mass average is appropriate because it is the mass integrated quantity which is conserved.

ii) If you are looking at static pressure, it is the area integral (force) which is conserved and thus the area average should be used.


  Reply With Quote

Old   February 22, 2015, 14:09
New Member
Join Date: Feb 2012
Posts: 14
Rep Power: 5
A.farid is on a distinguished road

I have a problem when calculating the mass average of the circumferential velocity component cu i found its value higher than the mass average of the absolute velocity c , how?!!!!!!

Can any on help me to know the reason.

A.farid is offline   Reply With Quote


Thread Tools
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 On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Starting field averaging using libFunctionObject after certain time eelcovv OpenFOAM Programming & Development 23 October 19, 2015 02:25
RANS - time averaging? Connor STAR-CCM+ 1 April 5, 2011 04:52
When to use mass flow averaging cspectre CFX 2 December 6, 2009 06:30
Averaging LES iko FLUENT 3 July 3, 2008 05:55
Start of averaging in LES fab Main CFD Forum 2 June 16, 2005 04:53

All times are GMT -4. The time now is 23:40.