Fluids

Fluids

Fluent: Access a transported scalar mass fraction in a UDF with the FGM model

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    • a.ortolani
      Subscriber

      Hi,

      I am using the flamelet generated manifold (FGM) model in Ansys Fluent and I am implementing a UDF using the macro "DEFINE_PDF_TABLE". 

      I am solving scalar transport equations for a couple of species in the mixture and in the UDF I can easily access their source terms (Get_Pdf_Tss_FwdRates(c, t, i)). I can also access the tabulated mass and mole fractions of all species (Get_Pdf_Xi(c,t,i)).

      What I can't do is to access the information about the mass (or mole) fraction of the transported species, i.e. the values computed in the CFD simulation. I couldn't find anything in the Customization manual.

      Can anyone help me?

      Thank you   

       

    • Rob
      Ansys Employee

      Does  C_YI(c,t,i) return what you're after?  I've turned on the Partially Premixed Model and have a PDF table and species reporting options. 

    • a.ortolani
      Subscriber

      Hi Rob,

      thank you for your answer.

      Unfortunatelly the C_YI(c,t,i) macro does not work with the partially premixed models. I need to use the Get_Pdf_Yi(c,t,i) macro which returns the value of the tabulated mass fraction, and not the one computed with the FGM scalar transport equation.

      I can easily get the information in post processing, but I would like to access it also in my UDF 

    • Rob
      Ansys Employee

      The post processing value is also taken from the pdf table: I think you've got the correct macro with Get_Pdf_Yi(c,t,i)  , it's covered in the UDF manual (apparently - a colleague is the expert). 

    • a.ortolani
      Subscriber

      As you say, in post processing I can access all the species concentration taken from the PDF table (Species.. > Mass fraction of ***). Those are the quantities that I can access in the UDF with Get_Pdf_Yi(c,t,i).

      What I would like to access in the UDF and I can't get is different. In post processing I find it in "Premixed Combustion... > Scalar Mass Fraction of ***"

    • Rob
      Ansys Employee

      Which may be calculated from the table. If it's not in the documentation I can't do much other than suggest checking the header files and retain all data (Section 3.2.3.7  https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v222/en/flu_udf/flu_udf_DataAccessMacros.html  )

    • a.ortolani
      Subscriber

      I didn't find any macro that suits my problem. To be clear, I am trying to acces the value of a scalar for which it is solved a transport equation. In particular I want the value of phi in equation 8-119 of the theory guide, which is found in section 8.3.2.3.1 "Scalar Transport with FGM closure" (https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v212/en/flu_th/flu_th_sec_par_premix_theory.html)

    • Rob
      Ansys Employee

      Then it may be stored under a different value, as I can't share anything that's no in the documentation I'm a bit stuck. 

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