Numerical simulation of surface positive jet in confluence flow

This study conducts a numerical investigation of effluent discharge in river confluences, focusing on jet behaviour under various hydrodynamic conditions. Aquatic ecosystems are frequently used as receiving environments for wastewater discharges, which can lead to complex phenomena impacting the ecosystem. To mitigate and manage these adverse effects, a thorough understanding of the interactions between effluents and receiving environments is crucial for promoting sound environmental management practices. To this end, the current study investigates the behaviour of a warm jet in crossflow when released near the surface at the confluence of channels. This paper specifically examines how discharge location and velocity affect the jet's trajectory, dilution, and mixing efficiency. Using OpenFOAM for numerical simulations, we analysed jets introduced into both the main and tributary channels, with a focus on different discharge velocities, particularly low-velocity discharges (Fr near one), which remain underexplored in the existing literature. Using the Large Eddy Simulation (LES) turbulence model, the numerical results showed strong agreement with experimental data, with an average error of approximately 4%, validating the model's accuracy. Key findings reveal that the confluence shear layer plays a significant role in shaping jet trajectories and enhancing mixing efficiency. Jets discharged in the main channel exhibited longer trajectories and greater interaction with ambient flow, resulting in higher dilution rates for both low- and high-velocity jets. Low-velocity jets were found to behave independently of jet velocity upon reaching the confluence, with their path being altered by the shear layer. Conversely, jets released in the tributary maintained a more consistent trajectory, unaffected by confluence dynamics.