Zero Diffusive flux

Subramani Sockalingam

I am running an external compressible flow steady state laminar model.I have modeled air as a reacting gas consisting of N2,O2,N,O and NO in FLUENT. I was able to run the simulation until Mach 12 after that it diverges with the error that mass diffusivity is zero. I have modeled mass diffusivity of the mixture using kinetic theory and I have defined the L-J parameters for all the species. I also tried to model using multi component diffusion by modeling the diffusion coefficients as polynomials for the interacting pairs. I got the same error after Mach 12. warning: Mass_Diffusivity: invalid (zero) diffusivity Please check material properties. Please give your thoughts on what could be wrong.

Thanks, Subramani