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

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]

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]

Originally Posted by ashgun

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]

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

[Saman95]

I have a question about calculating area weighted average

how to calculating it for a variable?

[Far]

Just go to surface integral. Choose the area weighted and choose your variable from list.

[Saman95]

yes I know,just by some simple click I can get Area weighted average.
you are cool

my mean is "Calculating with udf"

[Far]

Originally Posted by Saman95

I have a question about calculating area weighted average

how to calculating it for a variable?

my mean is "Calculating with udf"

How I can get that you meant UDF?

Any how you can look for those functions and write a udf. Refer to udf manual for samples.

[Saman95]

Originally Posted by Far

How I can get that you meant UDF?

Any how you can look for those functions and write a udf. Refer to udf manual for samples.

u are very clever