Numerical Model for Unidirectional Diffuser in a Crossflow

Abstract

This paper presents a mechanistic model to simulate multiple jets of a unidirectional diffuser discharging in shallow water with a strong crossflow. Due to the shallow water depth and close spacing of the jets, a sheltering effect is considered such that the presence of upstream jets reduces the crossflow velocity experienced by a jet. In addition, an induced flow field due to the entrainment of individual jets is calculated by considering point sinks located at jet nozzles and is superimposed on the ambient current. An integral model is used to simulate the trajectory and the mixing of the diffuser’s individual jets. Individual jets are considered to merge to form an aggregate jet when their inner boundaries intersect. An integral model is also used to calculate the trajectory and mixing of the aggregate jet. The sheltering factor, crossflow entrainment coefficient, and drag coefficient used in the model are calibrated using experimental observations of jet trajectory and dilution. The predictions of dilution at the edge of a mixing zone are shown to agree well with the observations for strong currents and moderate values of the ratio of jet spacing to water depth. The numerical model presented shows a significant improvement over existing models.