The diffusion coefficient in the turbulence module is estimated based on the eddy viscosity used in solution of the flow equations divided by at scaling factor sigma. For specification of the eddy viscosity (see Eddy Viscosity). The diffusion coefficient is calculated as the eddy viscosity coefficient divided by a Prandtl number.
You can specify the horizontal and vertical Prandtl number used in the transport equations for the turbulent kinetic energy, k, and the dissipation of TKE, e, repectively.