Finding the exact pressure applied by the fan boundary condition.

    • maria.marinari

      Hi there, I used a profile to apply a pressure jump across a fan boundary. I would like to calculate the total pressure jump that was applied across the boundary. Either by integrating over the area or finding the area-weighted average. This is difficult because the pressure is high before the jump and low after it and the simulation only seem to store the lower at the boundary. Is there any way to extract the exact pressure difference that is applied to the flow at the boundary?

    • Swathi V. V.
      Ansys Employee


      General practice is to create multiple planes before and after the fan boundary and calculate the area avg pressure value. The result section in the following document might be helpful for you.

      7.8. User-Defined Fan Model (ansys.com)


    • maria.marinari

      Hi Swathi!

      Thanks so much for your response!

      I believe I have attempted this method - would this be the same as control volume analysis?

      To get the results and you need to include the change in momentum across the volume as well as the change in pressure to figure out the pressure change that the fan is implying on the flow.


      I tried this but I keep getting an incorrect result for the mass flow rate out of the sides of the control volume that is why I thought I would ask this question.


      Finally thank you for attaching the link to the User-Defined Fan Model. Could the same model that is written there be written as a straight UDF in C. What is the purpose of the User-Defined Fan Model if UDF's already exist?


      All the best,



    • maria.marinari

      One way I could find the exact force that the fan is applying to the flow is by integrating the pressure profile I defined in the udf over the disk.

      I define the profile using the DEFINE_PROFILE Macro and its name is P_profile. 

      Is there a way to do this in the UDF? or report this as a custom field function to integrate over in 'Reports' automatically.

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