The macroscopic flow during processing of composite structures by liquid composite molding is accompanied by the microscopic flow through individual fiber bundles. This concurrent microscopic flow occurs at length and time scales different than those of the macroscopic flow and influences the macroscopic flow behavior, impacting the void formation during composite manufacturing. A reduced-order model developed by the authors of this paper in [Proc. 2005 ASME Conf., IMECE2005-82436] for modeling the microscopic impregnation of individual fiber bundles is currently used to simulate the transient dynamics of the 1-D two-phase flow though a dual-scale porous medium during resin transfer molding (RTM). As has been show in our previous work [Inter. J. of Multiphase Flow, Vol. 32, pp. 1219–1233, 2006] the vapor-liquid phase transition and multidimensional effects of the gas entrapped inside fiber tows can play a significant role in the advancement of the macroscopic resin front and the formation of voids, thus indicating the need to account for these phenomena in the simulation of liquid composite molding processes. These effects are quantified by introducing a nonzero sink term into the right hand side of the mass conservation equation for the dual-scale porous medium, which couples the microscopic two-phase flow inside fiber bundles with the macro-flow through the perform. Two numerical methods, one of which is based on the moving coordinate system associated with the macroscopic resin front and the other one based on the fill factor technique on a fixed Eulerian coordinate system, are used to solve the resin flow through the preform. The comparative analysis of the fill factor and moving front methods as well as the results demonstrating the effect of phase transition and impregnation of individual fiber bundles on macroscopic flow parameters during RTM are presented.
Pressure drop and average void fraction measurements for two-phase flow through highly permeable porous media
