In Phoenics CFD software, we can modify effecive thermal conductivity in energy equation by adjusting the thermal diffusivity. I want to know if we can do the same thing in FLUENT by UDF. The DEFINE_DIFFUSIVITY macro is not possible because it only can be used to specify the diffusivity for the species transport equations or user-defined scalar (UDS) transport equations.

Thanks a lot.

Thermal diffusivity is modeled by

k+cp*turb_viscosity/Pr_Energy

k is conductivity and cp specfific heat. You can set Prandtl number in the viscous panel either as constant value or udf. Unfortunatly there is no documentation about the needed macro (only for TKE and TDR Prandtl). In udf.h you can find (beside the two DEFINE_PRANDTL macros mention in the udf guide) three macros

#define DEFINE_PRANDTL_O(name, c, t) real name(cell_t c, Thread *t)

#define DEFINE_PRANDTL_T(name, c, t) real name(cell_t c, Thread *t)

#define DEFINE_PRANDTL_T_WALL(name, c, t) real name(cell_t c, Thread *t)

Maybe one of those will work.

Good Luck

RoM

Rom, thank for your help.