A model for the transverse permeability of bi‐material layered fibrous preforms

Abstract We consider viscous flow across unidirectional hexagonal arrays of porous tows of elliptical cross section. Using the lubrication approximation we develop an analytical model for the hydraulic permeability of layered systems, in which the permeability of the porous tows making up each alternating layer is allowed to differ. Extensive validation of this model is carried out through numerical computations using the Computational Fluid Dynamics package FIDAP. Good agreement between model predictions and numerically calculated permeabilities is found in the interesting region of small porosity (ϕ = 0.20 or ϕ = 0.30). Using this model we also address the issue of the inaccuracies that may be introduced if the overall permeability of a fibrous preform is calculated using an arithmetic average permeability instead of the actual permeability of each layer. We find that use of an average permeability will result in overestimation of the overall permeability of the system. This overestimation will increase as the porosity is reduced and/or as the difference in permeabilities increases.