Hi,i am trying to set boundary condition for species equation. I want to set a fix gradient of species at wall as the boundary condition. However, the fluent at wall boundary for species only has two options,one is to set species mass fraction, another is to set gradient of species equal to zero. Does anyone know how to set this kind boundary condition? Thanks a lot.

I think in your problem, mass fraction values will be solved for in the domain. thus the value at the boundary will need to be changed depending on the value of mass fraction in the cell next to the boundary. since you dont know that values till you have solution for the previous time step, you will have to use UDf to change the mass fraction value to maintain the gradient value. please refer to UDf manual. I think define_profile should work.