porocity

novice

Hi, I am simulating CFD problem with porosity first time and I want to know little more on alpha and beta of porous material. I am getting alpha and beta from experimental data, at the same time their values should be such that expression (alpha*U+beta)*L/(rho*U) >> 1. Here how to calculate U and L, i.e. characteristic velocity and characteristic overall dimension respectively. Your expert guidance is required. Thanks. -