[apolloking]

Hi,all. I have some questions about UDF of mass diffusivity in fluent
By default, FLUENT uses the dilute approximation, under which the diffusion flux can be written as

that means the mass diffusion coeffcient Di,m is a isotropic value,but in some papers,the mass diffusion coeffcient is an anisotropic value, the mass diffusion coeffcient in radial direction is different from that in axial direction. How can i define this in UDF. Thank you!