Darcy's Law?
 

Hi, everyone, excuse me with my english and with my probably stupid question, and please help me, i use ansys cfx v. 12.1; i cant understand which eqations cfx is using when finding velocity of a fluid through porous media.
it should be darcys law
(i know it in this form):
U = (K/mu)*grad(p)
where U is actual velocity
K is permeability tensor
p is pressure
mu is viscosity
grad() is gradient:)

but in darcy's law its necessary to know permeability tensor (or scalar, in isotropic model) to find velocity, and i set only porosity, and it seems, that permeability is used only in momentum loss model. so how it works, how it finds velocity without permeability.
in cfx-pre help i found such formula
U = -R^(-1)*grad(p),
where R is resistance to flow, second rank tensor,
U is actual velocity
and with such string "you obtain an anisotropic version of Darcy's law, with permeability proportional to the inverse of the resistance tensor"
its cool, but i dont set any resistance tensor or scalar and leave permeability blank empty, and i get velocity (superficial or actual, it is not important yet)
so help me please, and i will return to reading trying and studyin)