Mixing of Multiple Buoyant Jets

Abstract

Multiple buoyant jets are found in the natural and artificial environment: thermal discharges from fossil and nuclear-fueled electricity generation, domestic and industrial wastewater discharges, brine disposal from desalination plants, and various heat sources in the built environment. An overview of theoretical and experimental modeling of multiple buoyant jets over the past three decades is presented. Basic measurements of the structure of buoyant jet flows, integral jet modeling and three-dimensional numerical solutions of the Reynolds-averaged equations are reviewed. A semianalytical model is proposed to predict the dynamic interaction of multiple buoyant jets in stagnant fluid. The unknown jet trajectories are obtained from an iterative solution of an integral jet model and the irrotational external flow. Predictions are in good agreement with experiments of clustered jet groups, turbulent plume pairs, alternating diffusers, and rosette buoyant jet groups; the approach can also be extended to multiple jets in cross-flow. The mixing of a rosette buoyant jet group in a cross-flow is reviewed. The use of jet theory in solving two unconventional urban environment problems are highlighted: (1) the unraveling of the cause of the severe acute respiratory syndrome (SARS) outbreak in Hong Kong in 2003; and (2) design of a complex river junction for flood control under tight space constraints. It is suggested that experiments will remain a source of new theoretical ideas and the need for a civil engineer to solve complex problems with tractable models and analytical clarity will prevail.