Transient VOF analysis of geometry-controlled water ingress in residential sliding-window sills

Wind-driven rain (WDR) can cause water ingress through residential window-frame assemblies during tropical-cyclone events, even when structural failure does not occur. While external WDR exposure has been widely studied, the transient hydraulic response within sliding-window sill cavities remains less well quantified. This study presents a three-dimensional transient two-phase CFD investigation of water ingress through a residential sliding-window sill, focusing on the influence of internal drainage geometry. A Volume-of-Fluid (VOF) formulation was used to resolve air-water transport, cavity filling, internal pooling and leakage over a 5 s transient period. A sequential one-factor-at-a-time parametric study examined weep-hole length, drainage-channel length and number of drainage channels, with Fluent mass-flow-rate reports post-processed as time-increment water-mass metrics. The results show that weep-hole length is the dominant first-order control on water transport. Reducing the weep-hole length from 20 mm to 10 mm reduced the mean inlet and outlet transported mass metrics by approximately 48% and 54%, respectively. Drainage channels acted through a different mechanism, forming preferential drainage pathways and modifying the transient outlet response. The full-frame 10-channel case gave the lowest mean interior-outlet transport among the tested channel counts; a combined 10 mm weep-hole and 15 mm drainage-channel geometry was examined qualitatively. Instantaneous pressure excursions above 800 Pa were treated only as contextual loading indicators, not as CFD-based compliance criteria. The findings demonstrate that internal sill geometry strongly affects WDR-driven ingress and provides comparative evidence for the prescribed loading and 5 s observation window.