Desalination plants are becoming essential due to the limited water resources in order to reduce the pressure of high demand of freshwater in many countries in recent decades. A concerning problem associated with desalination plants is the high concentration brine which has high risk to marine environments. Inclined dense jets are commonly used to treat brine produced by desalination plants or in industrial outfall discharges. They are produced when the brine is discharged at an upwardly inclined angle through a pipe or a diffuser system. Previous studies have mainly focused on jets on a horizontal bottom. In the present study, the influence of sloped bottom is investigated by numerical simulations using a modified solver in OpenFOAM (pisoFoam). Four different Reynolds Averaged Navier Stokes (RANS) turbulence models (Realizable k-ε, Standard k-ε, RNG k-ε and Nonlinear k-ε were employed to assess the accuracy of the selected turbulence models in predicting the jet behavior. Jets of inclination angle of 30° with four different initial conditions (Froude number=15, 20, 25, 30) on three different bed slope angles (2°, 5°, 10°) in stagnant water were conducted. Although inclined dense jets of the discharge angel of 60° are more common in discharge systems, sometimes they cannot be used in shallow waters in order to prevent surface pollution. In such cases, a relatively small jet inclining angle can be used to prevent the surface pollution and as shown in this thesis, bed slope can enhance the brine mixing and dilution. The results showed that Realizable k-ε model is more accurate among the turbulence models studied herein. The dilution at the impact point can be estimated based on the Froude number and initial conditions. After the impact point, the slope did enhance the dilution of the plume compared to the horizontal bed. The dilution was thus affected by the slope and the dilution after the impact point on the slope appeared to be linearly related to the distance to the source. Besides, the slope could enhance the jet dilution up to 20% compared with the horizontal bed after the impact point.

Liquid wastes discharged from industrial outfalls have been researched for many years in the past. Majority of past studies, initiated in 1960s, were experimental studies mainly focused on basics of discharges such as key geometrical properties. Eventually, more robust experimental studies were performed to measure the mixing properties of effluent discharges with various jet configurations and ambient water conditions. Discharges could be as a means of submerged diffusers or surface channels and receiving water could vary from a homogenous calm ambient to a very complex stratified turbulent cross flow ambient. Depending on the bathymetric and economic situation around an outfall project, submerged discharges are preferred designs for most of ocean outfalls. It is the reason that majority of past studies have evaluated the mixing characteristics of submerged jets. Since early 1990s, the numerical modelling has emerged to support complex fluid mechanic problems. Later in 1990s and early in 2000s, the use of computational fluid dynamic (CFD) tools emerged in predicting the jet properties for the effluent discharges. Since then different numerical models have been developed for different applications. Similar to experimental studies, most of numerical studies have been focused on the submerged dense jet discharges. The current study intends to stay focused on the numerical modelling of such jets too; however, to cover the gaps in the literature. To achieve this, a thorough literature review was performed on the past CFD studies of over past 20 years to better understand what was done and what the gaps are. The results of this thorough review revealed that although there has been a great progress in the CFD studies in the field of effluent discharges, there are some applications that have not been investigated before, yet. It was found that there are some discharge inclinations that were not studied numerically before. Four discharge angles of 60°,75°, 80° and 85° were selected in this study, as previous studies mostly focused on 30° and 45°. The higher inclinations are more suitable for deep water outfalls where terminal rise height of the jet does not attach to the ambient water surface. The numerical model OpenFOAM was used in this study which is based on the Finite Volume Method (FVM) applying LRR turbulence model closure. LRR turbulence models was proved to be a capable choice for effluent discharge modelling. The second gap identified in the comprehensive literature review completed was the submerged dense effluent discharge into shallow water with surface attachment (for both inclined and vertical discharges). There was no previous numerical study of such jets identified. Three different regimes were identified: full submergence, plume contact and centerline impingement regimes (i.e. FSR, PCR and CIR). Key geometrical and dilution properties of these jets at surface contact (Xs, Ss) and return point (Xr, Sr) were extracted numerically and compared to those available from experiments. Two discharge angles (30° and 45°) were investigated based on the available experimental data. Five Reynolds-averaged Navier-Stokes (RANS) turbulence models were examined in this study: realizable k-ε and k-ω SST models (known as two-equation turbulence models), v2f (four equations to model anisotropic behavior) and LRR and SSG turbulence models (known as Reynolds stress models - six equations to model anisotropic behavior). Vertical dense effluent discharges are popular in the design of outfall systems. Vertical jets provide the opportunity to be efficient for a range of ambient currents, where the jet will be pushed away not to fall on itself. This research work investigates worst case scenario in terms of mixing and dilution of such jets: vertical dense effluent discharges with no ambient current and in shallow water where jet impacts the surface. This scenario provides a conservative design criteria for such outfall systems. The numerical modelling of such jets has not been studied before and this research work provides novel, though preliminary, insights in simulations of vertical dense effluent discharges in shallow waters. Turbulent vertical discharges with Froude numbers ranging from 9 to 24 were simulated using a Reynolds stress model (RSM), based on the results from inclined dense discharges to characterize the geometrical (i.e., maximum discharge rise Zm and lateral spread Rsp) and dilution μmin properties of such jets. Three flow regimes were reproduced numerically, based on the experimental data: deep, intermediate and impinging flow regimes.