hi there,

I'm doing UDS transport modelling in Fluent and have a diffusion coefficient which is a strongly non-linear function of the transported scalar. Does anyone know how the value of the diffusive coefficient is evaluated at the faces? The DEFINE_DIFFUSIVITY macro returns values for the cell centers, not for the faces. So I assume that the diffusive coefficient at the faces will be interpolated from the adjacent cell centers, but how?

thanks in advance

Hendrik-Jan

You should definie DEFINE_DIFFUSIVITY using user defined function. for example: DEFINE_DIFFUSIVITY(diffusivity_udf,cell,thread,i) { real przew; real T = C_T(cell, thread); if (T > 100.) { przew = 13990.; } else if ((T > 300.) && (T <= 1000.)) przew = 2.4430000000E-25*T - 1.9544000000E-22; } else if ((T > 1000.) && (T <= 2000.)) {przew = 2.8795570000E-22*T - 2.5913570000E-19; } else {przew = 22.} return przew; }