When acoustic waves propagate through a turbulent flow they will experience attenuation due to the turbulence. It can be shown theoretically (see Ref. 18 and Ref. 19) that the experienced attenuation corresponds to extending the value of the dynamic viscosity μ to include the eddy viscosity μτ, such that the total effective viscosity is:

This effect can be included in the linearized Navier-Stokes model by using the effective dynamic viscosity as taken from a CFD model spf.mu_eff. This variable includes the dynamic viscosity and the turbulent viscosity (spf.muT). Notice, however, that the value of the turbulent viscosity can be much larger than the true eddy viscosity and that it depends on the turbulence model selected. This means that the experienced attenuation can be too large. Typically, more advanced turbulence models like the SST model give less numerical diffusion and thus a better estimate of the eddy viscosity.