outlet pressure

Unknown
Unknown
edited March 2023 in Community Q&A

Hi all,

I was writing the pressure at outlet of my model to a file using UDF_OSI_PRESSURE. In the input file, I have specified the outlet pressure to be 24900000.000000 exactly. But, when I read the file, the Pout=24900004.555655382574. Is this discrepancy because of the averaging?

 

Thanks and regards,

Prabin

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Best Answer

  • acupro
    acupro
    Altair Employee
    edited March 2023 Answer ✓

    There are potentially two reasons for the difference in quantity.

    First - the pressure boundary condition is weakly enforced, and element boundary condition.  The solver does not set every node to that given value, but as you say, it is more of an averaged value.  It also somewhat depends on the convergence level and mesh resolution.

    Second - the OSI values from the surface integration process have contribution not only from the surface nodes or elements themselves, but also from the attached parent volume element.  Thus, again, there can be some deviation due to convergence level and mesh resolution.

Answers

  • acupro
    acupro
    Altair Employee
    edited March 2023 Answer ✓

    There are potentially two reasons for the difference in quantity.

    First - the pressure boundary condition is weakly enforced, and element boundary condition.  The solver does not set every node to that given value, but as you say, it is more of an averaged value.  It also somewhat depends on the convergence level and mesh resolution.

    Second - the OSI values from the surface integration process have contribution not only from the surface nodes or elements themselves, but also from the attached parent volume element.  Thus, again, there can be some deviation due to convergence level and mesh resolution.

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