Simulation of inclined dense jets in stagnant environments: an LES and experimental study

Inclined dense jets are commonly used to mitigate the environmental impacts of brine discharge in coastal desalination plants. Numerous studies have been performed to numerically simulate the sophisticated structures of the flow within this process. However, numerical prediction of the process is still a challenge. The present paper performs a comprehensive numerical study using the large eddy simulation (LES) approach on inclined dense jets oriented at angles 15°, 30°, 45°, 60°, and 75°, with a particular emphasis on the near-wall region, where the most complicated structures of the flow occur. The objective is to evaluate the capability of the LES approach to replicate the mixing processes of the brine jets. Besides numerical simulations, a series of experiments using the planar laser-induced fluorescence technique is carried out to compare each numerical simulation with its experimental correspondence. Both numerical and experimental results are presented in comparative figures compared to previous experimental data. The comparisons indicated that the LES model could reasonably predict the geometrical and mixing characteristics of inclined dense jets; however, the flow features are still underestimated by up to 25%. Moreover, the model could reproduce the local concentration build-up near the impact point. The processes within the near-wall region leading to this local decrease of dilution are discussed in detail. Additionally, a novel criterion is proposed to predict when the flow reaches a quasi-steady-state. The criterion can be used to manage the computational expenses, especially in simulations with high demanding computing power such as LES.