A pressure-consistent compressible fluid mixture model for predicting persistent air entrapment in resin transfer molding

Classical mold filling simulations for Resin Transfer Molding are typically based on incompressible single-phase Darcy flow combined with volume-of-fluid techniques to track the advancing flow front. While these approaches accurately predict macroscopic flow front propagation, they fail to capture persistent air entrapment, as flow-induced voids artificially vanish over time. To overcome this limitation, a pressure-consistent compressible fluid mixture model is proposed. The model consists of volume-averaged continuity equations for the air and liquid phases and a momentum equation including Darcy viscous losses, coupled through a closed-form equation of state. Air is modeled as an ideal gas and the liquid as a weakly compressible fluid, enabling the build-up of counter-pressure in entrapped regions without introducing additional empirical parameters compared to classical Darcy flow models. The model is implemented in the open-source simulation tool LCMsim and validated against a radial flow experiment with deliberately induced air entrapment. In contrast to conventional Darcy-based approaches, the proposed model predicts persistent air pockets and captures their compression during flow front convergence. Additional test cases demonstrate its capability to identify critical regions and assess the influence of venting strategies. The results show improved physical realism while maintaining computational efficiency suitable for industrial applications.