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YOĞUN DEŞARJ ÜZERİNE YAPILAN HESAPLAMALI AKIŞKANLAR DİNAMİĞİ (HAD) MODELLEME ÇALIŞMALARININ İNCELENMESİ
Abstract
Appropriate design of marine outfalls is of utmost importance for the safe disposal of brine,
which is the byproduct of the desalination process. A thorough analysis of brine jet behavior and mixing
and dilution in ambient environments is required for the optimum design. For these analyses, Computational
Fluid Dynamics (CFD) models have been increasingly used in recent years. In this paper, studies carried
out on dense discharges using different CFD software and turbulence models are systematically reviewed.
It was aimed to investigate the effects of differing discharge parameters on brine jet behavior and dilution
and to evaluate and compare the performances of different CFD software and turbulence models. Results
revealed that differing discharge parameters affect brine jet behavior and dilution significantly; different
models performed differently under altering discharge and ambient water conditions, and the use of the
most suitable model for optimum discharge is important.
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Seawater desalination is a reliable way to confront the growing challenges of freshwater demands in the world. Brine is the primary by-product of this process and needs to be carefully managed and discharged back into the sea. In coastal desalination plants, the use of submerged outfall as a pipeline laying on the ocean floor is a popular strategy to minimize the environmental impacts of brine discharge. The Venturi nozzle has been proposed as a more efficient method for dispersing brine into the ocean. However, it requires a high exit velocity, which poses limitations for steep nozzle angles in shallow waters. This study aims to investigate the benefits of a lower range of exit velocities in the Venturi nozzles. The 60° inclined dense jet from a Venturi nozzle was explored, numerically and experimentally, and the results were compared to those of a simple dense jet. Comparisons showed that the Venturi nozzle decreases the flow path and diminishes flow dilution at the critical points. However, this reduction can be compensated by increasing the discharge Froude number to reach the same trajectory as a simple jet. It is important to note that this compensation is intricately linked to the discharge velocity, and it makes the use of Venturi nozzles for brine discharge a challenging proposition in both deep and shallow waters.
Vertical dense effluent discharges are popular in outfall system designs. Vertical jets provide the opportunity to be efficient for a range of ambient currents, where the jet is pushed away so as not to fall on itself. This study focuses on the worst-case scenario of the dilution and mixing of such jets: vertical dense effluent discharges with no ambient current, in shallow water, where the jet impinges the water surface. This scenario provides conservative design criteria for such outfall systems. The numerical modelling of such jets has not been investigated before and this study provides novel insights into simulations of vertical dense effluent discharges in shallow waters. Turbulent vertical discharges with Froude numbers ranging from 9 to 24 were simulated using OpenFOAM. A Reynolds stress model (RSM) was applied 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.
Wastewaters are commonly discharged into the seas and oceans through multiport diffusers. Accurate prediction of the complex interactions of multiport diffusers with the receiving water bodies is significant for the optimal design of outfall systems and has yet to be fully illuminated. In the current study, the mixing and dilution characteristics of multiple inclined dense jets are studied using a three-dimensional numerical simulation. The Launder, Reece, and Rodi (LRR) turbulence model is employed to perform the simulations, and the predictions are compared against available experimental data. The results indicate that the LRR turbulence model is a promising tool for the study of inclined dense jets discharged from multiport diffusers, and it can provide more accurate predictions of the mixing behavior than standard and re-normalization group (RNG) k-ε turbulence models. The model is further employed to evaluate and compare the dispersion capabilities of multiport diffusers with uniform and non-uniform jet orientation to the horizontal, as a novel idea. The comparisons demonstrate the middle discharge may have a longer trajectory (7% and 5% increase in terminal rise height and impact point distance, respectively) and therefore a higher dilution rate (14% increase in impact dilution) when its adjacent jets are disposed with a different angle, compared to that of uniform discharges. The outcomes may be favorable for outfall systems applications involving dilution.
This paper presents the numerical results for inclined dense effluent discharges into a shallow receiving water body. Two jet discharge angles relative to the horizontal (30° and 45°) were investigated based on the experimental results from Jiang et al. (J Hydraul Eng 140:241–253, 2014). 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). Three mixing regimes introduced in Jiang et al. (J Hydraul Eng 140:241–253, 2014) were reproduced numerically for both discharge angles applying various turbulence models: 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 jet centerline return point (Xr, Sr) were compared to those available from experiments. Normalization parameter that was selected for jets in shallow waters is H/D (water depth above discharge point over nozzle diameter). It was found that surface attachment increases the return point length from the nozzle and that surface dilution decreases from FSR toward CIR. Among turbulence models tested herein, Reynolds stress models (LRR and SSG) predicted the effluent discharge kinematic and dilution properties better compared to two- and four-equations models. This is mainly attributed to the anisotropic nature of the effluent discharge problem studied herein and that these models are better capable to account for anisotropies.
Effluent discharge mixing and dispersion have been studied for many decades. Studies began with experimental investigations of geometrical and concentration characteristics of the jets in the near-field zone. More robust experiments were performed using Laser-Induced Fluorescence (LIF) and Particle Image Velocimetry (PIV) systems starting in the 20th century, which led to more accurate measurement and analysis of jet behavior. The advancement of computing systems over the past two decades has led to the development of various numerical methods, which have been implemented in Computational Fluid Dynamics (CFD) codes to predict fluid motion and characteristics. Numerical modeling of mixing and dispersion is increasingly preferred over laboratory experiments of effluent discharges in both academia and industry. More computational resources and efficient numerical schemes have helped increase the popularity of using CFD models in jet and plume modeling. Numerous models have been developed over time, each with different capabilities to facilitate the investigation of all aspects of effluent discharges. Among these, Reynolds-averaged Navier-Stokes (RANS) and Large Eddy Simulations (LES) are at present the most popular CFD models employing effluent discharge modeling. This paper reviews state-of-the-art numerical modeling studies for different types and configurations of discharges, including positively and negatively buoyant discharges, which have mostly been completed over the past two decades. The numerical results of these studies are summarized and critically discussed in this review. Various aspects related to the impact of turbulence models, such as k-ε and Launder-Reece-Rodi (LRR) models, are reviewed herein. RANS and LES models are reviewed, and implications for the simulation of jet and plume mixing are discussed to develop a reference for future researchers performing numerical investigations on jet mixing and dispersion.
In some outfall systems, wastewaters are discharged into ambient water bodies using rosette-type diffusers in the form of multiple buoyant jets, and it is essential to simulate their mixing characteristics for practical applications and optimal design purposes. The mixing processes of a rosette jet group are more complicated than single jets and multiple horizontal or vertical jets, and thus the existing methods cannot be effectively used to simulate their mixing and dilution properties. With the recent advancements in numerical modeling approaches, numerical simulation of wastewater jets as three-dimensional phenomena can be feasible. The present study deals with a fully three-dimensional numerical simulation for buoyant jets discharged from a rosette-type multiport diffuser, with the standard and re-normalization group (RNG) k-ε turbulence models. The simulated results are compared with experimental data, and the results show a good agreement with the experimental data, demonstrating that the numerical model is an efficient and effective tool for simulating rosette jet groups. It was also concluded that the RNG k-ε model leads to better results than the standard k-ε model with a comparable computational cost. The validated model was further utilized to investigate the influences of port inclinations on the mixing behaviors.
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.
Inclined submerged jets are mostly employed in the disposal of effluent produced by industrial sites such as desalination and power plants. The optimal design of discharge systems has been a topic of interest in many studies seeking to improve the mixing of effluent and reduce its negative environmental impacts. In addition to salinity, the effluent produced by thermal desalination units, which are usually built near power plants, has a high temperature compared to the marine environment and is mixed with hot power plant effluent, eventually forming thermal-saline effluent. The present study numerically modeled thermal-saline effluent using realizable k − ε turbulence model for a discharge angle of 45° in a uniform, stationary environment. The experimental results were used to calibrate the model results. Generally, the geometrical characteristics obtained from the numerical and physical models were in good consistency, which indicates the ability of the model in predicting the behavior of thermal-saline jets.
Seawater reverse osmosis (SWRO) desalination is increasingly used as a technology for addressing shortages of freshwater supply and desalination plants are in operation or being planned world-wide and specifically in California, USA. However, the effects of continuous discharge of high-salinity brine into coastal environments are ill-constrained and in California are an issue of public debate. We collected in situ measurements of water chemistry and biological indicators in coastal waters (up to ~2 km from shore) before and after the newly constructed Carlsbad Desalination Plant (Carlsbad, CA, USA) began operations. A bottom water salinity anomaly indicates that the spatial footprint of the brine discharge plume extended about 600 m offshore with salinity up to 2.7 units above ambient (33.2). This exceeds the maximum salinity permitted for this location based on the California Ocean Plan (2015 Amendment to Water Quality Control Plan). However, no significant changes in the assessed biological indicators (benthic macrofauna, BOPA-index, brittle-star survival and growth) were observed at the discharge site. A model of mean ocean wave potential was used as an indicator of coastal mixing at Carlsbad Beach and at other locations in southern and central CA where desalination facilities are proposed. Our results indicated that to minimize environmental impacts discharge should target waters where a long history of anthropogenic activity has already compromised the natural setting. To ensure adequate mixing of the discharge brine desalination plants should be constructed at high-energy sites with sandy substrates, and discharge through diffusor systems.
Desalination is the method of removing salts from brackish or saline water in order to produce fresh water. Due to rapid increases in populations and limitations to existing water supplies, this method has become essential source to provide fresh water demands. Thus, many large desalination plants, mostly coastal, have been constructed or are under construction around the world. Capital cost, high energy consumption, and environmental impacts are the main considerations involved in designing and operating of desalination plants. The main environmental concern, however, is the disposal of produced waste water back into the environment. The effects are mostly related to high salinity of brine produces during the process as byproduct. If the salt concentration is very high, making it denser than the ambient water, it is prone to plunge and spreads out over the floor, which increases the risk of negative effects on benthic ecosystems. So proper brine disposal is required to minimize the adverse impacts. The solution is to design marine outfall for rapid dilution to reduce salinity down to safe level. In this chapter, some of the essential issues involved in the management and modeling of brine discharges for coastal desalination plants are discussed.
Laboratory experiments on rosette diffusers for dense concentrate disposal from seawater desalination plants into flowing currents are reported. The dimensionless parameters for riser spacing and current speed were typical of operating diffusers. Three-dimensional laserinduced fluorescence (3DLIF) was used to map tracer concentration fields from which the main geometrical and dilution parameters were obtained. As the current speed increases, dilution and impact distance increase and rise height decreases. The results were insensitive to planform orientation of the risers. The rise heights of the rosette jets were always less than that of a corresponding isolated jet in a stationary environment. Semiempirical equations were presented to predict dilution, rise height, and impact distance, and confidence levels for the predictions were estimated. The results did not become independent of riser spacing in the range tested, in contrast to studies in stationary water where the flow properties became dependent on riser spacing for sr/dF < ~2. For narrow riser spacings and relatively slow current speeds, rosette diffusers have higher dilutions than equivalent conventional multiport diffusers, i.e., diffusers with the same length and number of ports, but for higher current speeds the rosette dilutions are significantly less than for the equivalent multiport diffuser.
Experiments are reported on multiport diffusers typical of brine disposal from desalination plants discharging into flowing currents. Diffusers discharging from one side into coflowing and counterflowing currents and from both sides were tested. A three-dimensional laser-induced fluorescence system was used to determine bottom impact dilution, impact location, and rise height. The results were plotted in dimensionless form as functions of port spacing and current speed parameters and empirical equations were fitted. As the current speed increased, the impact location was swept farther downstream, rise height decreased, and impact dilution increased. The merging of closely spaced jets prevents intrusion into the space between the ascending and descending regions, which can alter the flow fields. The results did not become independent of port spacing, at least within the parameter ranges studied and the experimental uncertainty. Raising the diffuser above the bed, which allowed the flow to pass beneath it, can affect the flow patterns significantly. Dilutions were not significantly affected, however, possibly because the nozzles were elevated above the pipe with a spacing that allowed passage of entrained flow between them. The dependence of the observed flow patterns on relatively small changes in source conditions should be considered in diffuser designs to avoid constricting the diluting entrainment flow.
Experiments were performed with a particle tracking velocimetry system to investigate the behaviour of inclined negatively buoyant jets with source angles of 15°, 30°, 45°, 60°, 65°, 70°, and 75° in stationary ambient conditions. Velocities were measured in a plane aligned with the central axis of the flow and the experiments were designed such that the flow did not interact with boundaries in the region were the flow behaviour was measured. The results of this study complement previous research, which has largely focused on the mean geometric characteristics and the mean dilution of the discharged fluid. Geometric characteristics, spreading rates, and time-averaged (mean) centreline velocity results are compared with relevant experimental results from previous studies and integral model predictions. Axial and transverse mean velocity profiles at maximum height and the return point provide additional insights into the detrainment of discharged fluid due to the unstable density gradient on the inner side of the flow.
Many municipal and industrial outfalls release effluent into water bodies. Temperatures and/or salinities of the effluent and receiving water may be different, and other dissolved/suspended constituents may be present. Away from the outfall, mixing processes usually reduce constituent concentrations to acceptable levels for local water quality. However, at the outlet, concentrations may be sufficient to cause environmental concern. Accurate dispersion prediction is therefore important. Two-stage modelling approaches are typically used: (1) a near-field dilution assessment, based on mixing zone or empirical models; and (2) a mid- /far-field dispersion assessment, using hydrodynamic models. As computational and numerical methods improve, computational fluid dynamics (CFD) can increasingly model dispersion across both regions. These methods require validation of the underlying discretisation and turbulence schemes. Preliminary validation is presented for near-field simulations of buoyant and dense jets. Buoyant jet predictions compare well with established results. Preliminary simulations under-predict entrainment into the dense jet, overly-predicting near-field concentrations.
Extensive Experiments on inclined dense jets typical of brine discharges into shallow water are reported. The experiments were conducted with nozzles oriented at 30°, 45°, and 60° to the horizontal and the spatial variations of tracer concentrations were measured by three-dimensional laser-induced fluorescence (3DLIF). Three flow regimes were identified: deep water, surface contact, and shallow water. The regimes depend on the value of dF=H, where d is the nozzle diameter, F the jet densimetric Froude number, and H the water depth; criteria were presented for the transitions between them. Flow images revealed complex three-dimensional interactions with the free surface, especially for steep nozzle angles in shallow water. Dilutions at critical points and their locations were measured. For deep water, all results followed those previously reported for fully submerged jets. As the depth decreases (or dF=H increases) to the surface contact regime, dilutions begin to decrease. Tracer concentration profiles are truncated at the water surface and in shallow water resemble half-Gaussian profiles similar to those of wall jets. The jets can cling to the water surface, although the locations of the bottom impact point and near-field length are not significantly affected by the water surface. In deep water and surface contact regimes, the impact point and near-field dilutions are highest for 60° nozzles. As the depth decreases further, however, the dilutions for the three nozzle angles become approximately equal, until, for shallow water, the 30°-nozzle gives slightly higher dilution. The 30°-nozzle may be preferable for this case because there is less surface interaction and, therefore, less visual impact on the water surface. Previous recommendations that dense jets be submerged so that the rise height to the jet's upper boundary be less than 75% of the water depth to avoid surface effects appear to be overly conservative and the present results suggest that the rise can be as much as 90% of the water depth for all angles with no deleterious effect on dilution.
Desalination is the method of removing salts from brackish or sea water in order to produce fresh water. Desalting is a natural and continual process which is an essential part of the water cycle. After rainfall, rain water carries dissolved minerals and other materials along the way to the sea, which makes the water increasingly salty. Through the sun’s energy, the evaporation of water leaves the salts behind and the resulting water vapor forms clouds that produce rain thus continuing the water cycle.
Laboratory experiments on single dense jets oriented at angles from 15° to 85° to the horizontal are reported. The major flow properties were measured by laser-induced fluorescence at the maximum rise height, impact point, and, for the first time, at the end of the near field. The impact point dilution was insensitive to nozzle angle over the range of about 45-65°. Because the additional mixing that occurred in the spreading layer beyond the impact point depended on nozzle angle, the near-field dilution was more sensitive to nozzle orientation and was highest for 60°, consistent with generally accepted design practice. Bottom boundary effects on dilution were also addressed. Along the jet centerline, time-average dilution first increased and then actually decreased in a thin layer up to the wall. The concentration increase near the bed is due to an increase in turbulent intermittency and accumulation of more saline fluid elements at the bed. The presence of this layer may explain wide discrepancies in reported dilutions near the boundary and may be environmentally important due to exposure of benthic organisms and sea grasses to high salinity. It may not persist, however, as it can be swept up by vortices that propagate radially away from the impact point. The vortices entrain ambient fluid leading to increased dilution, but they eventually collapse under their self-induced density stratification, marking the end of the near field.
An efficient method for increasing the dilution rate of brine water discharged into the sea is an inclined negatively buoyant jet from a single port or a multi-diffuser system. Such jets typically arise when brine is discharged from desalination plants. Two small-scale experimental studies were conducted to investigate the behaviour of a dense jet discharged into lighter ambient water. The first experiment concerned the importance of the initial angle of inclined dense jets, where the slope of the flow increased for the maximum levels as a function of this angle. An angle of 60 o produced better results than 30° or 45°. An empirical pre-dictive equation was developed based on five geometric quantities to be considered in the design of plants. The second experiment studied the near and intermediate fields of negatively buoyant jets. Dilution in the flow direction was increased by about 10 and 40 % with bottom slope, and bottom slope together with a 30° jet inclination, respectively. An over 16 % bottom slope experiment and more field work in the future are needed to compare with this result. It was found that an inclination of 30° with a 16 % bottom slope were optimal for the design of brine discharge outfall.
In this study, experimental and numerical investigations of the dense brine jets are conducted for disposal areas of limited extent. First, a new experimental model representing a section of sea floor with a single port brine outfall is built to study different characteristics of dense jets. Second, a number of numerical experiments have been conducted via Fluent CFD package to compare the numerical results with its corresponding physical observations and measurements. Experimental observations are made for both the terminal height of rise of dense jets discharged vertically from circular outlets into calm and homogeneous environment and for concentration profiles along the dense jet trajectory. Various combinations of port diameters and concentration of effluent salinities are investigated to cover a wide range of conditions. The results from the carried out experiments are compared to different available experimental and field observations from the literature. A new model for the terminal height of rise of dense jets has been derived. The experimental observations of concentrations along the dense jet trajectory are analyzed to quantify the mixing patterns for a given operating condition from the source point to the terminal height of rise. The numerical model has been used to identify the penetration depth and also to get the temporal variation of the brine breakthrough curves at different locations above the disposal port. The numerical model has shown the existence of multipeak breakthrough curves for the farest points from the port (but the closest to the water free surface).
Dispersion of turbulent jets in shallow coastal waters has numerous engineering applications. The accurate forecasting of the complex interaction of these jets with the ambient fluid presents significant challenge and has yet to be fully elucidated. In this paper, numerical simulation of 30∘ and 45∘ inclined dense turbulent jets in stationary water have been conducted. These two angles are examined in this study due to lower terminal rise heights for 30∘ and 45∘ , this is critically important for discharges of effluent in shallow waters compared to higher angles. Mixing behavior of dense jets is studied using a finite volume model (OpenFOAM). Five Reynolds-Averaged Navier–Stokes turbulence models are applied to evaluate the accuracy of CFD predictions. These models include two Linear Eddy Viscosity Models: RNG k−ε , and realizable k−ε ; one Nonlinear Eddy Viscosity Model: nonlinear k−ε ; and two Reynolds Stress Models: LRR and Launder–Gibson. Based on the numerical results, the geometrical characteristics of the dense jets, such as the terminal rise height, the location of centerline peak, and the return point are investigated. The mixing and dilution characteristics have also been studied through the analysis of cross-sectional concentration and velocity profiles. The results of this study are compared to various advanced experimental and analytical investigations, and comparative figures and tables are discussed. It has been observed that the LRR turbulence model as well as the realizable k−ε model predicts the flow more accurately among the various turbulence models studied herein.
Dense underflows are continuous currents that move downslope due to their density being heavier than that of the ambient water. In this work, a steady density current with a uniform velocity and concentration from a narrow sluice gate enters into a wide channel of lighter ambient fluid and moves forward downslope. Experiments varying inlet velocity and concentration and hence inlet Richardson numbers were conducted. Numerical simulations were also performed with a low-Reynolds number k-epsilon model. The results of numerical simulation agree well with the experimental data.
Analysis is performed to predict the maximum and equilibrium heights-of-rise for vertical round jets discharged into a linearly stratified crossflow. Approximate relations for minimum dilution at the maximum height of rise is also presented. Length scales describing the interaction of a buoyant jet with the crossflow and stratification are presented. Various asymptotic solutions can be developed with the use of dimensional analysis and physical reasoning; their applicability depends upon the relative magnitudes of the different length scales. Experimental results were obtained to determine the values of the appropriate coefficients in the various asymptotic solutions. These were obtained by towing a buoyant jet discharge at constant velocity through a stagnant, stratified fluid. Measurements of maximum and equilibrium rise heights were obtained along with concentration profiles at the maximum height-of-rise. The results indicate that the approximate solutions can be applied if the coefficients in the various expressions are allowed to vary; this variation may be small enough to neglect for many practical applications.
The coalescence of two co-flowing axisymmetric turbulent plumes and the resulting single plume flow is modelled and compared to experiments. The point of coalescence is defined as the location at which only a single peak appears in the horizontal buoyancy profile, and a prediction is made for its height. The model takes into account the drawing together of the two plumes due to their respective entrainment fields. Experiments showed that the model tends to overestimate the coalescence height, though this discrepancy may be partly explained by the sensitivity of the prediction to the entrainment coefficient. A model is then developed to describe the resulting single plume and predict its virtual origin. This prediction and subsequent predictions of flow rate above the merge height compare very well with experimental results.
The marine outfall system is used for disposal of effluent into the ocean. There is a strong belief that the ocean is an ultimate sink for the disposal of wastewater making sure that the disposed of effluent is within the standard disposal limits. For the large-quantity effluent discharge, multiport diffuser type marine outfall system is effective. The multiport diffuser is a series of main outfall pipe connected to the diffuser system with multiple nozzle ports connected in parallel to each other with an optimum spacing. In this study, the performance of the single round nozzle for buoyant fluids at a stable water condition in the unstratified water depth is carried out. The same is carried out for the multiple port round nozzle by varying the spacing distance between the consecutive ports. The numerical simulation for the single round nozzle for varying port outlet velocities is carried out achieving acceptable densimetric Froude number enhancing the performance of the round nozzle’s diffusion rate for the positively buoyant, neutrally buoyant and negatively buoyant effluent, and its respective plume characteristics are studied.
In this paper, the mixing and dilution characteristics of vertical buoyant jets discharged from multiport diffusers are studied numerically. The performances of four different turbulence closures are investigated, including the standard k-ε, renormalization group (RNG) k-ε, standard k-ω, and k-ω shear stress transport (SST) models, and the simulated results are compared to available experimental measurements. The comparisons demonstrate that a fully three-dimensional (3D) numerical model can be a reliable tool for the study of multiple vertical buoyant jets. Different fit measurement methods are employed to evaluate the turbulence models, and the results show that the predictions by the RNG k-ε model are the most accurate. The validated model is utilized to carry out additional computations with different port spacings and densimetric Froude numbers (Fr), and the simulated centerline and transverse concentrations at various cross sections are extracted and analyzed. The study reveals how varying port spacing and Fr affect multiple vertical buoyant jets. A new empirical formula that considers the port-spacing effect is proposed to describe the concentration decay along the jet centerline. The study also provides clues about merging points, well-mixed locations, and jet spread under the influences of port spacing.
A numerical investigation of near-field brine discharge dynamics is reported for the Gold Coast Desalination Plant offshore inclined multiport brine diffuser. Quasi-steady computational fluid dynamics simulations were performed using the Reynolds Averaged Navier Stokes equations with a k-ω Shear Stress Transport turbulence closure scheme. Simulations used an iterative mesh domain with length of 400 m, width of 200 m, and average depth of 24.2 m. Longshore crossflow conditions were examined with a current velocities range of 0.03-0.26 m/s. The alternating port orientation of the diffuser resulted in simultaneous co-and counterflowing discharges. Impact distance, impact dilution, and terminal rise locations were compared against the existing literature, and dimensionless empirical equations were fitted as functions of the current speed. Transverse spread and resulting salinity increases were also assessed against field measurements. For the first time, the areal extent of seafloor salinity increase is examined, with the quasi-quiescent regime holistically presenting the worst-case conditions. Plume trajectory, dilution, areal salinity intensity, and plume dispersion after impact each reflect distinct variations between jet-and crossflow-dictated regimes at a threshold value of urF ≈ 0.8 (ur = ambient to jet velocity ratio; F = jet densimetric Froude number). This behavior depends on the presence of the arrested upstream sublayer that, in turn, has consequences for the application of empirical models to multiport discharges under low-crossflow regimes. This study demonstrates significant advancements over existing empirical and integral modeling methods, with strong application potential for designers, plant operators, and regulators.
Detailed spatiotemporal analyses of near-field outfall dynamics are reported for an inclined brine multiport diffuser discharging into a dynamic open-coastal embayment. Three-dimensional variations in near-field discharge dynamics were captured using near-continuous in-situ monitoring of physicochemical properties in parallel with measurements of dissolved oxygen and ambient hydrodynamic conditions. Temporal analyses were conducted using principal component analysis and concentration–duration–frequency methods to show near-field salinity variations are generally localized to within 30 m of the diffuser and are highly sensitive to ambient crossflow dynamics. Periods of low near-bed velocities and high-velocity shear corresponded to the lowest return and boundary brine dilutions with instantaneous near-bed salinity increases of up to1.5 g/kg and dissolved oxygen (DO) reductions up to1.9 mg/L measured immediately downstream of the diffuser. Both trajectory and dilution demonstrated strong correlation with near-bed crossflow magnitude and were assessed against laboratory-based empirical models. Measured dilutions were well approximated by models that accommodate crossflow; however, trajectory properties were generally overpredicted. The quantitative characterization of temporal plume dynamics within an unsteady coastal setting provides valuable insights into the applicability of existing modeling approaches and regulatory assessment. Improvements to monitoring strategies are also proposed.
Atıksuların toplanması arıtılması uzaklaştırılması ve denizlere deşarjı su kaynaklarının ve çevrenin korunmasının ve sürdürülebilirliğinin sağlanabilmesi açısından büyük önem taşımaktadır. Bu çerçevede ülkelerin ekonomik kalkınmasına büyük katkı sağlarlar. Atıksuların toplanması arıtılarak uzaklaştırılması ve denizlere deşarjı doğru şekilde tasarlanmış ve uygulanmış mühendislik yapıları ile mümkündür. Aynı zamanda yapılan işin sürekliliği ve güvenilir olması da önemlidir. Yapım ve işletme maliyetleri çok yüksek olan bu tesislere ülkemizin her şehrinde ve kasabasında gereksinim duyulmaktadır. Atıksu arıtma toplama ve denize deşarjı sistemleri ihtiyaca göre ayrı ayrı yapılabildikleri gibi birlikte de planlanabilirler.
Su mühendisliğinin gerçekte birbiri ile iç içe olan bu üç önemli konusu kitapta detaylı bir şekilde ele alınıyor. Üç kısımdan oluşan kitabın birinci kısmında atıksuları toplama sistemlerinin ikinci kısımda atıksu arıtma sistemlerinin üçüncü kısımda ise denize deşarj sistemlerinin tasarım ve projelendirilmeleri ile ilgili esaslar veriliyor. Atıksu arıtma sistemleri konularında membranların uygulanması ile bilgilere de ayrıca yer veriliyor. Bu konular sistem boyutlandırma ve projelendirme örnekleri ve çözümlü problemlerle destekleniyor.
İçindekiler;
*Atıksuları Uzaklaştırma Sistemleri *Atıksuları Toplama Sistemleri *Atıksu Toplama Kanal Ağının Planlanması *Atıksu Kanallarının Hidrolik Hesabı *Atıksu Kanal Ağlarının Projelendirilmesi *Yağmur Suyu Giriş Yerlerinin Projelendirilmesi *Kanal Ağının Özel Yapıları *Atıksu Arıtma Yöntemleri *Atıksuların Arıtılması *Mekanik ve Fiziksel Arıtma *Biyolojik Arıtma *İleri Kademe Arıtma *Camurların Anaerobik Cürütülmesi *Camurun Kurutulması ve Uzaklaştırılması *Bir Atıksu Arıtma Sistemi İcin Boyutlandırma Örneği *Deniz Deşarjı Yapıları *Atıksu Deniz Deşarjı Sistemleri Tuzlu ve Yoğun Su Deşarjları
In the present study, we performed a numerical study with the Large Eddy Simulations (LES) approach to simulate inclined dense jets with 45° and 60° inclinations in a stagnant ambient, including the bottom impact and subsequent spreading on the wall boundary. The objective was to evaluate the performance of LES on the predictions of both the kinematic and mixing behavior of the inclined dense jet with bottom boundary in the near field region. The Dynamic Smagorinsky sub-grid model was adopted with near-wall modeling for the bottom boundary. The results showed that LES can reasonably predict the jet trajectory with the present mesh scheme, including the locations of the return point and impact point at the boundary. The localized concentration build-up at the impact point reported by Abessi and Roberts (2015) was also reproduced. The impact dilution was however underestimated by ∼20% in general corresponding to the grid resolution adopted in the present study, which demonstrated the challenge to simulate accurately the dynamics of the mixing behaviour as well as the wall interaction processes. The spreading layer was examined to the end of the near field region as defined by Roberts et al. (1997). The profiles of the mean concentration and concentration fluctuation along the spreading layer were found to be similar to previous experimental results with self-similar behaviour. The dilution was however also under-predicted within the spreading layer.
The near-field flow and mixing properties of vertical buoyant jets subjected to lateral confinement are studied numerically for different cases, including different confinement indexes and jet densimetric Froude numbers. The performances of different turbulence models are investigated, such as the standard k-∈ turbulence model and buoyancy-modified k-∈ model. The modeled results are compared to previous and present experimental observations. The present paper confirms that the universally accepted model (k-∈ turbulence model) can be satisfactorily accurate, eliminating the need for an advanced modeling approach, as long as suitable modifications are performed. In contrast to previous studies, which used one single and constant value of Ptr and Pr numbers, the present study links these two numbers to the F number, which is more practical and can produce very good results. This study also makes it possible to roughly quantify the rate at which the jet concentration spread width grows and identify the location where impingement occurs, which enables engineers or researchers to perform a quick estimation of the evolution and profile of a laterally confined vertical buoyant jet.
Wastewater disposal by marine outfalls is proven and effective and is a reliable and cost effective solution with minimal environmental impacts. The design and siting of submarine outfalls is a complex task that relies on many disciplines including oceanography, civil and environmental engineering, marine biology, construction, economics, and public relations. Marine Wastewater Outfalls and Treatment Systems brings these disciplines together and outlines all tasks involved in the planning and design of a wastewater system involving a marine outfall.
This book concerns the design of marine wastewater disposal systems: that is an ocean outfall plus treatment plant. All aspects of outfall design and planning are covered, including water quality design criteria, mathematical modelling of water quality and dilution, gathering required oceanographic data, appropriate wastewater treatment for marine discharges, construction materials for marine pipelines, forces on pipelines and outfall design, outfall hydraulics, outfall construction, tunnelled outfalls, operation and maintenance, monitoring, case studies are discussed and methods for gaining public acceptance for the project are presented. Finally, costs for many outfalls around the world are summarized and methods for estimating costs are given.
This is the first book to consider all aspects of marine outfall planning and construction. The authors are all extensively involved with outfall schemes and aware of recent developments. The science and technology of all aspects of outfall discharges into coastal waters and estuaries of treated municipal or industrial wastewater has advanced considerably over the past few years. Marine Wastewater Outfalls and Treatment Systems provides an up to date and comprehensive summary of this rapidly developing area.
ISBN: 9781843391890 (Print)
ISBN: 9781780401669 (eBook)
Because of their toxicity, brines must often be diluted when discharged to fresh or saline water using multiple port diffusers. These negatively buoyant jets behave quite differently from wastewater jets, which are lighter than the seawater to which they are often discharged. A theoretical and laboratory study of brine dilution after discharge from an outfall into a flowing stream was completed. Initial analysis was based on studies conducted on disposal of brine into still water; a laboratory study was conducted to obtain concentration profiles for various current velocities and angles of the discharge port. Comparison of experimental results with a jet theory relying on entrainment and drag shows that the theory predicts dilutions much lower than those obtained. The apparent reason for the inadequacy of the theory is that it ignores ambient turbulence.
This study experimentally investigates the effect of shallow water depth on the mixing of 30 degrees and 45 degrees inclined dense jets. Three different mixing regimes were identified, namely, the full submergence, plume contact, and centerline impingement regimes. The mixing characteristics in these three regimes, including the jet trajectory and minimum dilution at the water surface (SS) as well as at the return point near the seabed (Sr), were quantified with respect to the densimetric Froude number (F) and cover water depth (H). The nondimensional cover water depth, H/D, was found to be a suitable normalization parameter for shallow water scenarios. The transitional F center dot D/H among the regimes, the asymptotic limits of the minimum surface dilution at large F, and the various linear coefficients were also determined. Overall, it was found that the surface constraint in the plume contact and centerline impingement regimes, lengthens the jet-spreading distances and reduces the surface dilution, while the bottom dilution remains relatively constant. The results enable the assessment of the mixing characteristics of the inclined dense jet in shallow coastal waters with possible surface contact for environmental impact assessment.
A comprehensive laboratory study of negatively buoyant discharges is presented. Unlike previous studies, here the focus is on generating data sets where influences of the bottom boundary have been eliminated. There are significant discrepancies in the published dilution data for these flows and a contributing factor is the large variation in the bottom boundary condition. A Laser-induced Fluorescence system is employed to gather flow spread, peak concentration (minimum dilution) and trajectory data for a wide range of densimetric Froude numbers and initial discharge angles. Data from these experiments are compared with previously published data, along with predictions from integral models and a revised form of the previously published semi-analytical solutions. The new data sets are not distorted by mixing processes associated with the bottom boundary and therefore provide the basis for more meaningful assessments of the predictive capabilities of existing models, given that the influences of the bottom boundary on contaminant mixing are not incorporated into these models. In general the models assessed are able to predict key geometric quantities with reasonable accuracy, but their minimum dilution predictions are conservative. Importantly dilution at the return point shows a strong dependence on the initial discharge angle and this could have important implications for the design of discharge systems.
This paper reports results of a comprehensive experimental investigation of inclined round dense jets in an otherwise stagnant fluid. The tracer concentration field is measured for six jet discharge angles: θo = (15°, 30°, 38°, 45°, 52°, & 60°) and jet densimetric Froude number of Fr = 10–40 using the planar laser-induced fluorescence (LIF) technique; selected jet velocity measurements are made using Particle Image Velocimetry (PIV). The detailed jet mixing characteristics and turbulence properties are presented. The direct velocity measurement reveals that the mixing is jet-like until the maximum rise. Empirical correlations for the maximum jet rise height, jet dilution at maximum rise, and impact dilution are presented. Both the time-mean concentration and intermittency show that the upper jet edge spreading is similar to a positively buoyant jet; at the lower edge the buoyant instability induces significant detrainment and mass outflux for θo > 15°. The dimensionless maximum rise height Zmax/(FrD) is independent of source conditions for Fr ≥ 25, and varies from 0.44 for θo = 15° to 2.08 for θo = 60°. Dilution measurements at terminal rise show the difference in dilution is small for θo = 38°–60° and the asymptotic dilution constant is St/Fr = 0.45. The impact dilution Si is also not sensitive to jet angle for θo = 38°–60° and can be expressed as Si/Fr = 1.06 for Fr ≥ 20.The Lagrangian jet model VISJET is used to interpret the experimental results. A detailed derivation for a general formulation of the entrainment coefficient is presented. Despite the observed detrainment, the trajectory and dilution are reasonably predicted; the maximum jet rise is generally under-predicted by 10–15% and associated dilution by 30%. However, the predicted variation of jet behavior with discharge angle is in good agreement with measurements. The experimental data is also compared with predictions of alternative models that employ an ad hoc entrainment hypothesis.
A general Lagrangian jet model formulation is presented for an inclined buoyant jet in a current, with a three-dimensional trajectory. The shearinduced entrainment is computed as a function of the local densimetric Froude number and jet orientation, while the forced entrainment is taken as the ambient flow intercepted by the "windward" side of the buoyant jet. Model predictions are compared with both trajectory and tracer concentration data for a wide range of discharge and ambient flow conditions: horizontal buoyant jets in a coflow; vertical jets, oblique jets, and dense plumes in a cross flow; buoyant jets in a stagnant uniform or stratified fluid; and a horizontal buoyant jet in a perpendicular cross flow. The model is also consistent with the concept of asymptotic flow regimes, and reproduces the correct behavior in both the near and far field of a vertical momentum of buoyancy-dominated jet in a cross flow. The connection of the model with traditional integral jet models is also discussed.
Sea water desalination plants discharge a concentrated brine effluent into coastal waters. Modern, large capacity plants require submerged discharges, in the form of a negatively buoyant jet, that ensure a high dilution in order to minimize harmful impacts on the marine environment. Existing design practice favors a steep discharge angle of 60° above horizontal, a practice based on limited and outdated laboratory data for dilutions at the level of maximum rise. Examination of more recent laboratory data and the parametric application of a jet integral model suggest that flatter discharge angles of about 30-45° above horizontal may have considerable design advantages. These relate to better dilution levels at the impingement location, especially if bottom slope and port height are taken into account, there is better offshore transport of the mixed effluent during weak ambient current conditions, and there is the ability to locate in more shallow water near shore.
In this work experimental data on the geometry of dense inclined jets issuing in a lab-scale glass rectangular tank are presented. The surrounding fluid was always tap water at room temperature while the dense jets were water solutions of NaCl. Four parameters were changed in the experiments, namely nozzle diameter and inclination, and jet density and flow rate. Jet trajectories were revealed by a colored tracer. Images of the jet were recorded by a digital camera and then further digitally processed, eventually resulting in a time-averaged tracer intensity field. All the jet geometrical parameters, once normalized, were found to be very well correlated to the densimetric Froude number. Moderate jet viscosity variations were found to not significantly affect jet behavior. The reported data allow a quick and easy estimation of maximum rise level, position of the trajectory maximum, and impact point distance of dense jets issued at different angles above the horizontal. Journal of Hydraulic Engineering
An extensive series of experiments on the characteristics of inclined and vertical dense jets discharged into a uniform crossflow of various speeds and directions is reported. The inclined jets were maintained at 60° to the horizontal and the results for terminal rise height, and dilutions at the terminal rise height and impact points are compared to those for vertical jets. For discharges into stagnant ambients, it is f6und that the effect of source volume flux should not be neglected for jet Froude numbers less than about 25. Empirical equations to predict dilution and rise height based on dimensional and length scale arguments are presented. The dilution of an inclined jet increases as the angle to the current increases. Dilutions for inclined jets discharging into the crossflow are lower than for a vertical jet and dilutions for discharges with the crossflow are generally higher. Applications to design are discussed, and it is found that the inclined jet is generally preferable to the vertical jet. This is because of the lower rise height of the inclined jet, the much higher dilution under stagnant conditions, and the horizontal momentum given to the wastefield.
Well planned natural ventilation strategies and systems in the built environments may provide healthy and comfortable indoor conditions, while contributing to a significant reduction in the energy consumed by buildings. Computational Fluid Dynamics (CFD) is particularly suited for modelling indoor conditions in naturally ventilated spaces, which are difficult to predict using other types of building simulation tools. Hence, accurate and reliable CFD models of naturally ventilated indoor spaces are necessary to support the effective design and operation of indoor environments in buildings.
This paper presents a formal calibration methodology for the development of CFD models of naturally ventilated indoor environments. The methodology explains how to qualitatively and quantitatively verify and validate CFD models, including parametric analysis utilising the response surface technique to support a robust calibration process. The proposed methodology is demonstrated on a naturally ventilated study zone in the library building at the National University of Ireland in Galway. The calibration process is supported by the on-site measurements performed in a normally operating building. The measurement of outdoor weather data provided boundary conditions for the CFD model, while a network of wireless sensors supplied air speeds and air temperatures inside the room for the model calibration.
The concepts and techniques developed here will enhance the process of achieving reliable CFD models that represent indoor spaces and provide new and valuable information for estimating the effect of the boundary conditions on the CFD model results in indoor environments.
An integral model for the plane buoyant jet dynamics resulting from the interaction of multiple buoyant jet effluxes spaced
along a diffuser line is considered as an extension of the round jet formulation that was proposed in Part I. The receiving
fluid is given by an unbounded ambient environment with uniform density or stable density stratification and under stagnant
or steady sheared current conditions. Applications for this situation are primarily for submerged multiport diffusers for
discharges of liquid effluents into ambient water bodies, but also for multiple cooling tower plumes and building air-conditioning.
The CorJet model formulation describes the conservation of mass, momentum, buoyancy and scalar quantities in the turbulent
jet flow in the plane jet geometry. It employs an entrainment closure approach that distinguishes between the separate contributions
of transverse shear and of internal instability mechanisms, and contains a quadratic law turbulent pressure force mechanism.
But the model formulation also includes several significant three-dimensional effects that distinguish actual diffuser installations
in the water environment. These relate to local merging processes from the individual multiple jets, to overall finite length
effects affecting the plume geometry, and to bottom proximity effects given by a “leakage factor” that measures the combined
affect of port height and spacing in allowing the ambient flow to pass through the diffuser line in order to provide sufficient
entrainment flow for the mixing downstream from the diffuser. The model is validated in several stages: First, comparison
with experimental data for the asymptotic, self-similar stages of plane buoyant jet flows, i.e. the plane pure jet, the pure
plume, the pure wake, the advected line puff, and the advected line thermal, support the choice of the turbulent closure coefficients
contained in the entrainment formulation. Second, comparison with data for many types of non-equilibrium flows with a plane
geometry support the proposed functional form of the entrainment relationship, and also the role of the pressure force in
the jet deflection dynamics. Third, the observed behavior of the merging process from different types of multiport diffuser
discharges in both stagnant and flowing ambient conditions and with stratification appears well predicted with the CorJet
formulation. Fourth, a number of spatial limits of applicability, relating to terminal layer formation in stratification or
transition to passive diffusion in a turbulent ambient shear flow, have been proposed. In sum, the CorJet integral model appears
to provide a mechanistically sound, accurate and reliable representation of complex buoyant jet mixing processes, provided
the condition of an unbounded receiving fluid is satisfied.
Predictions from a k-ε model are compared with recently acquired experimental data from inclined negatively buoyant discharges. The k-ε model is part of a standard computational fluid dynamics package (CFX). Two approaches are taken when implementing the model.
One involves using an essentially standard form of the model to predict flow behaviour. The other approach involves calibrating
the model, through adjustment of the turbulent Schmidt number in the tracer transport equation, to achieve reasonable predictions
for positively buoyant vertical discharges and then applying it to inclined negatively buoyant discharges. While the calibrated
approach improves the predictions of some bulk parameters (notably the tracer spread and dilution) when compared to predictions
from the standard model, the overall effect on the quality of the predictions is small. Comparisons with experimental data
indicate that predictions from both the standard and calibrated simulations compare favourably with trajectory data, but integrated
dilution predictions at the centreline maximum height are conservative (mean-integrated concentrations are over-predicted).
The standard and calibrated k-ε predictions confirm the importance of buoyant instabilities on the lower (inner) side of the flow, the effects of which are
clearly evident in the mean concentration profiles. However, these simulations have a tendency to overestimate the influence
of stabilizing density gradients on the upper (outer) side of the flow and are unable to effectively predict the cross-sectional
distribution of a tracer. In contrast to a previous study, the above comparisons indicate that predictions of bulk parameters
from such models can be poor and indeed are no better than those obtained from relatively simple analytical solutions.
The mechanics of buoyant jet flows issuing with a general three-dimensional geometry into an unbounded ambient environment with uniform density or stable density stratification and under stagnant or steady sheared current conditions is investigated. An integral model is formulated for the conservation of mass, momentum, buoyancy and scalar quantities in the turbulent jet flow. The model employs an entrainment closure approach that distinguishes between the separate contributions of transverse shear (leading to jet, plume, or wake internal flow dynamics) and of azimuthal shear mechanisms (leading to advected momentum puff or thermal flow dynamics), respectively. Furthermore, it contains a quadratic law turbulent drag force mechanism as suggested by a number of recent detailed experimental investigations on the dynamics of transverse jets into crossflow. The model is validated in several stages: First, comparison with basic experimental data for the five asymptotic, self-similar stages of buoyant jet flows, i.e., the pure jet, the pure plume, the pure wake, the advected line puff, and the advected line thermal, support the choice and magnitude of the turbulent closure coefficients contained in the entrainment formulation. Second, comparison with many types of non-equilibrium flows support the proposed transition function within the entrainment relationship, and also the role of the drag force in the jet deflection dynamics. Third, a number of spatial limits of applicability have been proposed beyond which the integral model necessarily becomes invalid due to its parabolic formulation. These conditions, often related to the breakdown of the boundary layer nature of the flow, describe features such as terminal layer formation in stratification, upstream penetration in jets opposing a current, or transition to passive diffusion in a turbulent ambient shear flow. Based on all these comparisons, that include parameters such as trajectories, centerline velocities, concentrations and dilutions, the model appears to provide an accurate and reliable representation of buoyant jet physics under highly general flow conditions.
The US Environmental Protection Agency has a history of developing plume models and providing technical assistance. The Visual Plumes model (VP) is a recent addition to the public-domain models available on the EPA Center for Exposure Assessment Modeling (CEAM) web page. The Windows-based VP adapts, modifies, and enhances the earlier DOS-based PLUMES with a new interface, models, and capabilities. VP is a public platform for mixing zone models designed to encourage the continued improvement of plume theory and models by facilitating verification and inter-model comparison. Some examples are presented to illustrate VP’s new capabilities. One demonstrates its ability, for reasonably one-dimensional estuaries, to estimate background concentrations due to tidal re-circulation of previously contaminated receiving water. This capability depends on the optional linkage to time-series input files that enables VP to simulate mixing zone and far-field parameters for long periods. Also described are the new bacterial decay models used to estimate depth changes in first-order decay rates based on environmental stressors, including solar insolation, salinity, and temperature. The nascent density phenomenon is briefly described as it is potentially important to Outer Continental Shelf (OCS) oil exploration discharges.