Displacement flow in an enclosure containing multiple buoyancy sources: A review

Buoyancy-driven displacement flow in ventilated enclosures is a key mechanism in natural ventilation, indoor stratification, and contaminant removal. This review provides a structured synthesis of theoretical and experimental studies on displacement flows driven by localized buoyancy sources, focusing on stratified-interface formation and predictive modeling for multiple-source configurations. The review is organized around a unified framework in which buoyant plumes entrain ambient fluid, form layered stratification, and drive unidirectional flow through upper and lower openings. For a single buoyancy source, the classical emptying–filling box model shows that the steady interface height is governed mainly by the dimensionless effective opening area and plume entrainment coefficient, whereas upper-layer buoyancy depends on source strength. For two sources at the same elevation, unequal plumes generate three-layer stratification, with interface positions controlled by opening area, enclosure height, and source-strength ratio. When sources are located at different elevations, additional regimes arise because source position relative to the stratified layers determines which plume supplies the intermediate or upper layer. Representative models are compared in terms of assumptions, governing parameters, treatment of entrainment and mixing, predicted quantities, and applicability. Recent developments involving virtual-source correction, interfacial entrainment, upper-layer depth restrictions, and regime classification are also discussed. By clarifying the relationships, strengths, and limitations of existing models, this review provides guidance for selecting appropriate approaches to predict interface heights, stratification regimes, and ventilation performance in naturally ventilated buildings and related buoyancy-driven flows.