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-   -   Strange averaging in directMappedFixedValue BC (http://www.cfd-online.com/Forums/openfoam/77482-strange-averaging-directmappedfixedvalue-bc.html)

 woody June 24, 2010 08:28

Strange averaging in directMappedFixedValue BC

Dear All,

while trying to derive my own BC from the direct mapped BC, i was wondering why there are two different averaging possibilities:

Code:

```  if (setAverage_)     {         Type averagePsi =             gSum(this->patch().magSf()*newValues)           /gSum(this->patch().magSf());         if (mag(averagePsi)/mag(average_) > 0.5)         {             newValues *= mag(average_)/mag(averagePsi);         }         else         {             newValues += (average_ - averagePsi);         }     }```
Any Idea about the streching if the average differs to much?

Have FUN!

 florian_krause September 7, 2012 05:10

Quote:
 Originally Posted by woody (Post 264335) Dear All, while trying to derive my own BC from the direct mapped BC, i was wondering why there are two different averaging possibilities: Code: ```  if (setAverage_)     {         Type averagePsi =             gSum(this->patch().magSf()*newValues)           /gSum(this->patch().magSf());         if (mag(averagePsi)/mag(average_) > 0.5)         {             newValues *= mag(average_)/mag(averagePsi);         }         else         {             newValues += (average_ - averagePsi);         }     }``` Any Idea about the streching if the average differs to much? Have FUN!
Hi guys,
I am successfully using the mapped BC for LES of turbulent flow through a 90deg bend, with the mapping region located in an (extended) straight inlet section. I switched on averaging of velocity to obtain my desired bulk velocity.

While running the simulation, I assumed that OF always computes the new velocities according to the above else statement, using the difference between the desired average and the current velocities. Then I checked the corresponding code and I'm also a bit confused by the same the if statement, specifically by the condition and the first correction method.

Any ideas?

Thanks,
Florian

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