Before revision: The Reynolds number (a dimensionless parameter) for porous media flow is typically expressed as where is the kinematic viscosity of water, is the specific discharge (not the pore velocity — with units of length per time), is a representative grain diameter for the porous media (the standard choice is d30, which is the 30% passing size from a grain size analysis using sieves — with units of length).
After revision: math|The Reynolds number (a dimensionless parameter) for porous media flow is typically expressed as where is the kinematic viscosity of water, is the specific discharge (not the pore velocity — with units of length per time), is a representative grain diameter for the porous media (the standard choice is d30, which is the 30% passing size from a grain size analysis using sieves — with units of length).