Permeability modeling and electric-hydraulic analogy for unidirectional tows

This study investigates the permeability of fiber tow domains using ANSYS Fluent simulations and an approximation method based on an electric-hydraulic analogy derived from Darcy's Law and Ohm's Law. The permeability of a hexagonally distributed fiber structure is calculated using a representative unit cell modeled in ANSYS Fluent. Fibers are modeled as solid regions, allowing resin to flow through the spaces between them. Permeability is determined by applying Darcy's Law to the computed flow rate, showing strong agreement with Gebart's analytical solution. In a larger scale, the overall permeability is determined by simulating resin flow through a unit cell of ten fiber tows, where tows are treated as porous regions with resin flowing through both inter-tow and intra-tow channels. A variety of tow distribution scenarios are examined, including manually designed extreme cases and random distributions generated in MATLAB, emphasizing the impact of tow spacing perpendicular to the flow direction on flow channels and permeability. The permeability approximation method aligns with simulation results, while significantly reducing computational cost and time. Key factors such as domain size, tow spacing, and intra-tow porosity are analyzed. Comparisons between simulated and approximated permeabilities highlight the limitations of the method under varying domain sizes and intra-tow porosities. The results show that the approximation improves in accuracy as intra-tow porosity decreases and domain height increases, due to the predominance of resin flow in inter-tow channels. This study's primary contribution is offering a scalable and efficient permeability prediction approach applicable to a range of tow configurations, providing valuable insights for optimizing resin flow in composite manufacturing processes.