Modelling of Dense Jet in Co-Flow and Counter Flow

Abstract

Wastewater effluents with a density higher than that of the environment are often discharged into coastal waters in the form of submerged dense (negatively buoyant) jets. Examples include brine discharge from desalination plants, cooled water from liquefied natural gas plants and gypsum waste from fertilizer factories. It is necessary to design dense jet discharges to achieve rapid mixing and minimize the environmental impact. Currently, however, there is no generally accepted predictive model for the mixing of a dense jet in a current. In the present study, numerical modelling of mixing and near-intermediate field interactions of upward discharged dense jet is carried out. The near field behaviour of the jet is computed by the Lagrangian jet model JETLAG. The mixing and transport in the intermediate field is predicted by dynamically coupling a three-dimensional (3D) shallow water circulation model with JETLAG using a Distributed Entrainment Sink Approach (DESA). Simulation of inclined dense jet in stagnant water and flowing current has been undertaken. The 3D model is able to simulate the initial rise and fall of the jet as well as the spreading layer along the bottom. The computed dilutions agree well with those obtained from the laboratory experiments, which demonstrate the feasibility of using the DESA method to compute the mixing of dense jet in a current.