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-   -   Diffference between mass weighted average and Area (http://www.cfd-online.com/Forums/fluent/46942-diffference-between-mass-weighted-average-area.html)

 giogio January 3, 2008 05:00

Diffference between mass weighted average and Area

Hi, I don't understand the difference between Mass weighted average and area weighted average, when i must use one or the other. (results are very different).

Thanks

 Glenn January 8, 2008 13:19

Re: Diffference between mass weighted average and

Mass averaging is summation of (value * mass flow) / summation of mass flow over the surface of interest. Area averaging is summation of (value * area) / summation of area over the surface of interest.

 ashgun September 24, 2012 13:13

regarding mass weighted average velocity

Hi,
i just want to know that is average velocity( mass weighted ) dependent on grid number ? Actually i am simulating flow through pipe , and flow is laminar so friction factor theoretical is 64/ Re . And flow is fully developed(done using C coding) .for Re 500 f th is 0.128. and i am getting 0.145 and its not acceptable i guess. U max is 0.01817. So actual avg. velocity value should be 0.01284813 but fluent giving me d value 0.012135. Can anyone tell me whats going wrong or how to improve avg. velocity value (mass weighted )

Since flow is laminar we cant get actual pressure drop(static) and its coming out 0.2396 and fluent giving me 0.24 so its close only problem is with velocity plz. tell what is wrong

 syavash September 24, 2012 16:42

Quote:
 Originally Posted by ashgun (Post 383373) Hi, i just want to know that is average velocity( mass weighted ) dependent on grid number ? Actually i am simulating flow through pipe , and flow is laminar so friction factor theoretical is 64/ Re . And flow is fully developed(done using C coding) .for Re 500 f th is 0.128. and i am getting 0.145 and its not acceptable i guess. U max is 0.01817. So actual avg. velocity value should be 0.01284813 but fluent giving me d value 0.012135. Can anyone tell me whats going wrong or how to improve avg. velocity value (mass weighted ) Since flow is laminar we cant get actual pressure drop(static) and its coming out 0.2396 and fluent giving me 0.24 so its close only problem is with velocity plz. tell what is wrong
I guess nothing! Fluent solves the fluid flow numerically, so it's obvious that there would be difference in comparison with analytical solution.When dealing with computational methods, you have to consider range of acceptable numerical error, for instance 5%. Here you may try to adjust your mesh in order to get desired solution.

 ashgun September 25, 2012 01:36

I tried with 0.1 million cell count and 0.6 million, only i could see decrease in pressure drop but average velocity remained same

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