Fluids

Fluids

How to write UDF for Dynamic viscosity??

    • Devank12
      Subscriber

      I have one dynamic viscosity equation which is depend on fluid temperature and i want to apply that equation in a flow through a pipe. So how to  write the user defined function. .

    • DrAmine
      Ansys Employee

      Search in the Fluent customization for the macro DEFINE_PROPERTY and create the expression for the viscosity, 

    • klu
      Ansys Employee

      Add to abenhadj, the macro to access cell temperature is C_T(c,t).

    • seeta gunti
      Ansys Employee

       Hello Devank,


       


      You can refer Fluent Customization documentation under "Detailed Examples". In that, DEFINE_PROPERTY macro is explained with an example of a variable viscosity  profile to simulate the solidification. You can try the similar UDF with dynamic viscosity profile. Hope this help you.

    • Devank12
      Subscriber

      #include "udf.h"


      DEFINE_PROPERTY (cell_viscosity,c,t)


      {


      real mu;


      real temp = C_T(cell, thread);


      mu =2.414*e-05* double pow(double 10, double 248/T-140);


      return mu;


      }


      i have developed a UDF for dynamic viscosity . i dnot know which is correct. if any correction plz inform me

    • Nownesh
      Ansys Employee

      Hello


      In DEFINE_PROPERTY (cell_viscosity,c,t), and  real temp = C_T(cell, thread);... c,t and cell & thread names should be consistent. 

    • DrAmine
      Ansys Employee

      #include "udf.h"


       


      DEFINE_PROPERTY(cell_viscosity,c,t)


      {


      real mu = 1e-5;


      real fac = 1.0;


      fac = 248.0/(C_T(c,t)-140.0);


      mu =2.414*exp(-0.5)*pow(10.0,  fac);


      C_UDMI(c,t,0) = mu;


      return mu;


      }


       


      Please check the customization manal and attend a UDF Training.

    • dsub5
      Subscriber

      hello everyone. i have to create udf for dynamic viscosity and thermal conductivity coefficient. but have no idea about codes.

      here is the formulas. if anyone can help me, i wii be glad.



      mu=(3.4*10^-7*T^2)-(2.3*10^-4*T)+(3.9*10^-2)

      k=0.004961*T-0.8078

    • ziadkoussa
      Subscriber

      hello, 


       


      i am running the same udf you posted as i need the same values however after i interpret the udf and change the viscosity to user defined, when i try to initialise and calculate i get an error message saying "f1 process could not be started" and fluent automatically closes. 


      Help please

    • DrAmine
      Ansys Employee
      Try to compile.
    • ziadkoussa
      Subscriber

      Hi Amine, 


       


      thank you for your help. 


       


      Is there anything i need to change in the code to compile? (I am still new to ansys) 


       


      Thanks

    • DrAmine
      Ansys Employee

      You need to install a compiler. Check in the forum for several Compiler threads. In your case your using the UDF I Posted I guess. Please check if you have defined a User Memory in Fluent.

    • Eirene2015
      Subscriber

      Wrong help provided by abenhadj, 


      made me go through a whole day learning how to compile the UDFs, but the issue is the fact that his syntax is wrong. 


      C_UDMI(c,t,0) is not defined yet, so you cannot allocate values to it, thus the user receives a segmentation fault error!


      This UDF does not require compilation. A simple interpret will work as long as the issue of C_UDMI(c,t,0) is omitted. 


      Do not wast time in compiling this code as I did!

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