Learning Forum

[Bovinille Anye Cho]

Hello all, how can one access the turbulent viscosity for transitional SST model in a UDF for further calculations? This is needed in my investigation to estimate the turbulent diffusivity for later solving a specie transport equation.

Although the turbulent viscosity is visible in the GUI, I have tried the macro C_MU_T(c,t) in a User Define Memory (UDM) but it doesn’t work as seen the attached picture. It seems this macro only works for the k-e and k-w models.

I tried storing in UDMs other variables such as turbulent kinetic energy (with C_K(c,t)), specific dissipation rate (with C_O(c,t)) and strain rate magnitude (with C_STRAIN_RATE_MAG(c,t)), to calculate it according to Menter’s work. However, only the former macro works as the others (i.e., C_O(c,t) and C_STRAIN_RATE_MAG(c,t)) didn’t work.

Also, I can create a custom field function for turbulent viscosity in the GUI but how does one access this within a UDF? Is there way to pass custom field functions into UDM for UDF calculations?

[Mark Owens]

Hi, it should work. It works here in testing, at least back to version 2022R2. C_MU_T is the turbulent viscosity for k-e, k-w and transition SST models. Have you hooked your UDF function into the meaterial properties for the UDS diffusivity? You could add the line

Message("c_mu_t = %e \n", C_MU_T(c,t));

to your UDF and run for 1 iteration to see what is happening. Only macros documented in the Customization manual are supported.

[Bovinille Anye Cho]

Hello Mark,

Thanks for your reply. I'm running on an ealier version (2022R1), my UDF is hooked into the material property, tried a few iterations and it doesn't work. 

Nonetheless, I have been able to use the custom feild function and patch it into a user define memory, and then read the UDM within the UDF, it works. Thanks. 

 

[Mark Owens]

OK, great. I am glad you have a workaround. However, it also works for me in 2022R1 so I can't be sure that upgrading would resolve your issue. No matter what I try, I cannot reproduce what you are seeing. "mut" is a predefined variable so maybe your compiler is doing something strange there. You could try renaming it to udf_mut. If that doesn't work then it would require a deeper investigation that we cannot provide through the forum.