Good day.

I think you need to evaluate the dissipation rate at the boundary. My evaluation example is very formalistic, because turbulent exchange does not exist here:

Eps = k3/2 / le , where k-turbulent kinetic energy (5-10% of mean kinetic energy), le- scale size for pores.

I think the effective viscosity will be near molecular value at the boundary. 

With best regards,

Serge.

Thanks @Serge

Hi Sergii

OK for the Serge's answer but are you sure to have a turbulent flow ?