Effect of dual scale porosity on the overall permeability of fibrous structures

Abstract The effect of various parameters on the overall permeability of a two dimensional dual scale fibrous structure is studied employing computational fluid dynamics. The permeability of the structure is computed using two models; one resolved and one with homogenised porosity. The homogenised porous tow model is compared with the resolved model to the level of resolution the resolved model can provide at reasonable computational cost. Good agreement is found between the two numerical models. The porous homogenised tow model is then used to study the effect of inter-tow and intra-tow porosity on the overall permeability. It is shown that the effect of intra-tow porosity on the overall permeability is insignificant, while the inter-tow porosity on the other hand has a very strong influence on the overall permeability. Good correlation is also shown with results from previous experimental and numerical studies. For relatively low tow to filament radius ratios ( R t / R f ) there can be some influence from the intra-tow porosity on the overall permeability. However, it is negligible for higher ratios ( R t / R f > 10 2 ), i.e. in the regime where most fibre reinforcements for composite materials are found.