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-   -   Area Weighted Average Velocity is Not Correct (https://www.cfd-online.com/Forums/fluent/186859-area-weighted-average-velocity-not-correct.html)

CaptainCombo April 24, 2017 11:57

Area Weighted Average Velocity is Not Correct
 
Hi all,

In Fluent area weighted average of inlet velocity is not giving correct Uavg value. Here is my way to define fully developed velocity profile;

1. Solve the problem at uniform Uavg velocity for one time step
2. Write the inlet velocity profile to PROF file
3. Calculate the fully developed velocity profile by using formula U(r) = 2*Uavg*(1-(r^2/R^2)). Here "r" values are teaken from PROF file.
4. Copy fully developed velocity values to PROF file
5. Read the PROF file from Fluent

In Fluent area weighted average of inlet velocity must be equal to Uavg written in formula at step 3. However there are significant error between correct value and the Fluent.

LuckyTran April 24, 2017 16:18

How significant is the mismatch?

Quote:

Originally Posted by CaptainCombo (Post 646302)
In Fluent area weighted average of inlet velocity must be equal to Uavg written in formula at step 3.

Your formula is analytical whereas Fluent is dealing with a discretized velocity with a grid. In general, using only an analytical formula to calculate the desired velocity profile, you cannot guarantee the average velocities to match.


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