Effect of Proximity to Bed on 30° and 45° Inclined Dense Jets: A Numerical Study

Employing inclined dense jets is a common way for the disposal of brine effluent from coastal desalination plants. This paper numerically analyzes the mixing and geometrical properties of 30° and 45° inclined dense jets when they discharge close to the bed. For this purpose, two series of numerical simulations were developed. First, the nozzle acts as a free jet when it is placed far enough from the lower boundary. Meanwhile, in the second series, the distance between the nozzle tip and seabed is substantially reduced. Consequently, by comparing these two series, the effect of proximity to bed on the behavior of dense jets is investigated. The governing equations are solved by modifying a solver within the CFD package of OpenFOAM. The numerical results are presented in comparative figures and compared to the previous works. Comparisons indicated that the numerical model predicts the geometrical characteristics of dense jets in good agreement with the past experimental studies. However, the dilution predictions are conservative. It has been observed that proximity to the bed has almost no appreciable effects on the behavior of 45° jets. However, for 30° jets, when the bed proximity parameter ( Y0/LM ) falls below 0.14, normalized values of horizontal and vertical locations of centerline peak and return point dilution are slightly reduced while the terminal rise height remains untouched.

Numerical Modeling of Multiple Inclined Dense Jets Discharged from Moderately Spaced Ports

Wastewaters are often discharged into water bodies from multiport diffusers in the form of inclined dense jets, and it is important to predict their mixing characteristics for a sound sustainable design for seawater desalination. Compared with single jets and multiple horizontal or vertical jets, the mixing processes of multiple inclined dense jets are more complicated, and thus the existing theoretical, analytical, or simplified numerical methods cannot effectively predict their dilution properties. Recent advances in numerical modeling techniques have provided a new avenue of simulating wastewater jets as three-dimensional phenomena, but their application to multiple inclined dense jets has rarely been reported. In this study, a fully three-dimensional numerical model is employed to simulate multiple inclined brine discharges from diffusers with moderately spaced ports, with the standard and re-normalization group (RNG) k-ε turbulence closures being tested. The simulated characteristic variables are compared to experimental data, and the results show that the simulations match very well with the experiments, demonstrating that the numerical model is a promising tool for simulating inclined dense jets discharged from multiport diffusers. The study also found that the RNG k-ε model performs better than the standard k-ε model without significantly increasing the computational costs.