Dense jet behaviour in dynamic receiving environments

The discharge of brackish water, as a dense jet in a natural water body, by the osmotic power plants, undergoes complex mixing processes and has significant environmental impacts. This paper focuses on the mixing processes that develop when a dense round jet outfall perpendicularly enters a shallow flowing current. Extensive experimental measurements of both the salinity and the velocity flow fields were conducted to investigate the hydrodynamic jet behavior within the ambient current. Experiments were carried out in a closed circuit flume at the Coastal Engineering Laboratory (LIC) of the Technical University of Bari (Italy). The salinity concentration and velocity fields were analyzed, providing a more thorough knowledge about the main features of the jet behavior within the ambient flow, such as the jet penetration, spreading, dilution, terminal rise height and its impact point with the flume lower boundary. In this study, special attention is given to understand and confirm the conjecture, not yet experimentally demonstrated, of the development and orientation of the jet vortex structures. Results show that the dense jet is almost characterized by two distinct phases: a rapid ascent phase and a gradually descent phase. The measured flow velocity fields definitely confirm the formation of the counter-rotating vortices pair, within the jet cross-section, during both the ascent and descent phases. Nevertheless, the experimental results show that the counter-rotating vortices pair of both phases (ascent and descent) are of opposite rotational direction.

A comprehensive experimental investigation for an inclined (\(60^{\circ }\) to vertical) dense jet in perpendicular crossflow—with a three-dimensional trajectory—is reported. The detailed tracer concentration field in the vertical cross-section of the bent-over jet is measured by the laser-induced fluorescence technique for a wide range of jet densimetric Froude number \(Fr\) and ambient to jet velocity ratios \(U_r\). The jet trajectory and dilution determined from a large number of cross-sectional scalar fields are interpreted by the Lagrangian model over the entire range of jet-dominated to crossflow-dominated regimes. The mixing during the ascent phase of the dense jet resembles that of an advected jet or line puff and changes to a negatively buoyant thermal on descent. It is found that the mixing behavior is governed by a crossflow Froude number \(\mathbf{F} = U_r Fr\). For \(\mathbf{F} < 0.8\), the mixing is jet-dominated and governed by shear entrainment; significant detrainment occurs and the maximum height of rise \(Z_{max}\) is under-predicted as in the case of a dense jet in stagnant fluid. While the jet trajectory in the horizontal momentum plane is well-predicted, the measurements indicate a greater rise and slower descent. For \(\mathbf{F} \ge 0.8\) the dense jet becomes significantly bent-over during its ascent phase; the jet mixing is dominated by vortex entrainment. For \(\mathbf{F} \ge 2\), the detrainment ceases to have any effect on the jet behavior. The jet trajectory in both the horizontal momentum and buoyancy planes are well predicted by the model. Despite the under-prediction of terminal rise, the jet dilution at a large number of cross-sections covering the ascent and descent of the dense jet are well-predicted. Both the terminal rise and the initial dilution for the inclined jet in perpendicular crossflow are smaller than those of a corresponding vertical jet. Both the maximum terminal rise \(Z_{max}\) and horizontal lateral penetration \(Y_{max}\) follow a \(\mathbf{F}^{-1/2}\) dependence in the crossflow-dominated regime. The initial dilution at terminal rise follows a \(S \sim \mathbf{F}^{1/3}\) dependence.

Dense granular impinging jets widely exist in natural flow phenomena and industrial processes, such as the rapid heating, cooling or drying, and gasification. It is important to investigate the factors influencing the flow patterns of dense granular impinging jets and reveal the evolution rules of the flow patterns. The dynamic behaviors of the dense granular impinging jets are experimentally studied by a high-speed camera and image processing software of Image J. The effects of the particle diameter, the granular jet velocity (u0) and the solid content of the granular jet (xp) on flow pattern of the granular impinging jet are investigated. Two flow regimes of the dense granular impinging jets, i.e., the liquid-like granular film and the scattering pattern, are identified. The results show that with the increase of the particle diameter and the granular jet velocity, both the solid content of the granular jet and the inter-particle collision frequency decrease, which results in the transition of granular sheet to scattering pattern. With the increase of granular jet velocity, the opening angle of the granular sheet from the side view increases, while the opening angle from the front view increases first and sharply decreases later. The results also show that with the increase of the granular jet velocity, the liquid-like granular film becomes unstable and a non-axisymmetric oscillation appears. And the amplitude and frequency of the liquid-like granular film increase with granular jet velocity increasing, and are significantly affected by particle diameter. The interesting behaviors of the liquid-like surface waves are observed on the granular sheet. The surface waves become remarkable with the increase of the granular jet velocity, and their propagating velocities normalized by the granular jet velocity vary from 0.7 to 0.9. The waves propagating on the granular sheet may emerge, which will reduce the frequencies of the surface waves and increase the surface wavelengths. The results also show that the oscillation frequency of the granular film nearly equals the pulsation frequency of the granular jet. It is indicated that the gas-solid interaction inside the nozzle increases with granular jet velocity increasing, and causes the instability of the granular jet, resulting in the non-axisymmetric oscillation on the granular sheet consequently. The results in this paper present significant knowledge of the dense granular impinging jets and also provide some principles for the applications in dense granular impinging jets in industrial processes.

Dense granular jet impingement widely exists in numerous natural flow phenomena and industrial processes. It is significant to investigate the influencing factors of the flow patterns of dense granular jet impingement and reveal the evolution rules of flow patterns. The dynamic behaviors of dense granular jets impinging on a flat target are experimentally studied by a high-speed camera and image processing software of NIH. The effects of the particle diameter（Dpar), the granular jet velocity（U0) and the solid content of the granular jet（X) on the flow patterns and surface waves of granular sheet are investigated. Two patterns, i.e., the liquid-like granular film and the scattering pattern are identified from the dense granular jet impingement. The results show that with the increase of the particle diameter, the solid content of the granular jet reduces, and the interparticle collision frequency decreases, which results in the granular sheet evolving into the scattering pattern. The opening angle of the granular sheet（) is bigger than that of the liquid sheet, and the granular jet velocity plays an insignificant role in the opening angle. The interesting behaviors of liquid-like surface waves are identified in the granular sheet. The frequency of surface wave of the granular sheet（f) is an order of magnitude smaller than that of the liquid sheet. The surface wave length（) increases and frequency decreases with the increase of radial position, as the surface waves merge during the granular sheet spreading radially. The surface wave spreading velocity normalized by the granular jet velocity is a constant of about 0.4. With the increase of the granular jet velocity, the pulsation of granular jet occurs due to the pressure fluctuation in the discharge process under the effect of gas-solid interaction. The frequencies of surface waves of both the granular sheet and the granular jet pulsation become the same generally. It is indicated that the surface wave is primarily caused by the granular jet pulsation. The results in this paper present the knowledge of the dense granular jet impingement and provide some principles for the steady operation of dense granular jet impingement in industrial process.

60° inclined dense jets had been recommended for brine discharges from desalination plants to achieve a maximum mixing efficiency. However, the terminal rise associated with 60° is relatively high and thus the angle may be too large for disposal in shallow coastal wasters. In this study, we investigate the mixing behavior of dense jets discharging at smaller angles of 30° and 45° in a stationary ambient. Combined Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) were used as the measurement approaches that captured the velocity and concentration fields, respectively. Based on the experimental results, the characteristic geometrical features of the inclined dense jets, including the location of the centerline peak and the return point where the dense jet returns to the source level, etc., are quantified. The mixing and diluting behaviors are also revealed through the analysis of the axial and cross-sectional velocity and concentration profiles. In addition to the free inclined discharges, the present study also examines the effect of the proximity to the bed. Through the comparison of the results between two experimental series with distinct z 0/D but overlapping z 0/L M , the latter is identified as the deciding factor for the boundary influence.

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 $$30{^\circ }$$ and $$45{^\circ }$$ 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 $$30{^\circ }$$ and $$45{^\circ }$$ , 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 $$ k-\varepsilon $$ , and realizable $$k-\varepsilon $$ ; one Nonlinear Eddy Viscosity Model: nonlinear $$k-\varepsilon $$ ; 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 $$k-\varepsilon $$ model predicts the flow more accurately among the various turbulence models studied herein.

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 60o produced better results than 30° or 45°. An empirical predictive 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.

Inclined dense discharge in stagnant and wave environments: An experimental and numerical study

ABSTRACTPouring coolant into molten material provides an efficient method for cooling molten core debris in light water reactor. This coolant jet-melt interaction mode needs to be studied for proposed application and safety concern. The jet breakup pattern and its final depth are crucial factors for efficient cooling. In the present study, the hydraulic penetration behavior of coolant jet is investigated using experimental and numerical approaches. A series of visual experiments are conducted using low-density gasoline as coolant jet and high-density water as molten fuel. The images of jet behaviors and the data of gasoline jet penetration depth are obtained and analyzed. Based on FLUENT15.0 a 3D axisymmetric model is built and Volume of Fluid (VOF) method is used. The hydraulic penetration behaviors of jet and final penetration depth are correctly simulated and analyzed. The fluctuating phenomenon of penetration depth and the effects of various parameters are discussed. Jet velocity and density ratio are key factors to final penetration depth. The conclusions are helpful to understand the parameter influence and the fluctuation mechanism of final penetration depth and substantiate the understanding of the coolant jet hydraulic penetration behavior during coolant jet-melt interaction.

This thesis primarily focuses on understanding the plasma behavior during the helicity injection stage of a pulsed spheromak experiment. Spheromak formation consists of a series of dynamic steps whereby highly localized plasma near the electrodes evolves toward a Taylor state equilibrium. The dynamical evolution stage has been modeled as a series of equilibrium states in the past. However, the experiments at the Caltech spheromak facility have revealed that unbalanced J x B forces drive non equilibrium Alfvenic flows during these preliminary stages. The Caltech spheromak experiment uses coplanar electrodes to produce a collimated plasma jet flowing away from the electrodes. The jet formation stage precedes the spheromak formation and serves as a mechanism for feeding particles, magnetic helicity, energy, and toroidal flux into the system. Detailed density and flow velocity measurements of hydrogen and deuterium plasma jets have revealed that the jets are extremely dense with β [subscript thermal] ~1. Furthermore, the flow velocity was found to be Alfvenic with respect to the the toroidal magnetic field produced by the axial current within the plasma. An existing magnetohydrodynamics (MHD) model has been generalized to successfully predict the effect of plasma current on the jet's density and flow velocity. The behavior of these laboratory jets is in stark contrast to the often considered model for astrophysical jets describing them as equilibrium configurations with hollow density profiles. Other contributions of this thesis include the following. 1. The thesis presents an analytical proof that resistive MHD equilibrium with closed flux tubes is not feasible. This implies that sustained spheromak experiments cannot maintain helicity while being in a strict equilibrium. 2. The thesis describes measurements to characterize the circuit parameters of the high voltage discharge circuit used in the Caltech spheromak experiment. 3. The thesis also describes the setup of novel He-Ne laser interferometers used to measure the density of plasma jets. The ease of alignment of these interferometers was greatly enhanced by having unequal path lengths of the scene and reference beams. 4. Finally, the thesis details the setup for a soft X-ray (SXR)/Vacuum ultra violet (VUV) imaging system. Some preliminary images of reconnecting flux tubes captured by the imaging setup are also presented.

A 3D model is established to discuss the influence of combustion reaction on jet characteristics. Based on this, combustion behaviors of supersonic jet for single‐flow postcombustion oxygen lance with various secondary nozzle parameters (diameter, inclination angle, and number) are analyzed. The results indicate that after activating combustion reaction, the jet velocity, dynamic pressure, density, and temperature of primary jet at H = 1.45 m are 1.27, 1.15, 0.56, and 1.97 times than those of without considering the combustion, respectively. Enlarging secondary nozzle diameter is helpful to extend the flame core lengths of primary and secondary jets (the axial distance from lance tip to isotherm of 1773 K) as well as the combustion region. With the increase of secondary nozzle angle, the two flame core lengths both decrease, while the combustion zone increases. Increasing the number of secondary nozzles, the flame core length of primary jet increases while that of the secondary jet decreases, and the combustion region first increases and then decreases. As for the influences of the above parameters on flame core lengths of primary and secondary jets as well as the combustion region, the number is the greatest, followed by the inner diameter, and the inclination angle is the smallest.

In order to study the damage effect of PTFE/Al/W reactive jet against reinforced concrete, AUTODYN-3D numerical simulation was used to study the formation and penetration behaviors of reactive jets with densities of 2.31g/cm3~4.12g/cm3. Simulation results show that under the same charge condition, the diameter of low-density reactive jet is larger, and there is no significant difference in the axial velocity distribution of the reactive jets with different densities. For the damage effect of reinforced concrete, the penetration hole diameter of reinforced concrete formed by low-density reactive jet is larger, moreover, the steel bars can protect the concrete and reduce the damage area of concrete surface. For the penetration ability, the reactive jets with different densities can penetrate the front layer of steel bars, and the higher density of reactive jet, the deeper penetration depth of reinforced concrete. Meanwhile, hitting position of the jet against concrete target has significant effect on penetration results. The broken steel bars in penetration hole reduce the penetration depth.

The effect of some of the important flow parameters, such as, velocity ratio, density ratio and momentum ratio have been examined experimentally on potential core length of the cryogenic fluid injected from a single-element coaxial injector. The injector simulated one element of the cryogenic rocket engine injectors under realistic operating conditions. This work focuses specifically on the evolution of liquid nitrogen jet instability and breakup under steady state atmospheric conditions. The results showed significant role of velocity ratio, density ratio, momentum ratio along with the strong heat transfer effect of the surrounding atmosphere on the cryogenic liquid nitrogen jet behavior. The potential core length of the cryogenic liquid nitrogen showed a local peak as a function of velocity of the gaseous jet. However, the core length showed insensitivity to changes in density of the gaseous jet. The results also provided a strong evidence of the heat-shielding effect of the coaxial gaseous jet. The heat transfer from the surroundings to the cold LN2 jet is reduced significantly by the presence of the gaseous jet, which strongly affects the potential core length of liquid nitrogen jet. The experimental diagnostic technique used here is Schlieren imaging using a high speed camera to analyze the global flow behavior of liquid nitrogen jet. The Schlieren images were processed using image processing techniques to obtain quantitative information of the flow.

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.

Liquid waste discharged from industrial outfalls is categorized into two major classes based on their density. One type is the effluent that has a higher density than that of the ambient water body. In this case, the discharged effluent has a tendency to sink as a negatively buoyant jet. The second type is the effluent that has a lower density than that of the ambient water body and is hence defined as a (positively) buoyant jet that causes the effluent to rise. Negatively/Positively buoyant jets are found in various civil and environmental engineering projects: discharges of desalination plants, discharges of cooling water from nuclear power plants turbines, mixing chambers, etc. This thesis investigated the mixing and dispersion characteristics of such jets numerically. In this thesis, mixing behavior of these jets is studied using a finite volume model (OpenFOAM). Various turbulence models have been applied in the numerical model to assess the accuracy of turbulence models in predicting the effluent discharges in submerged outfalls. Four Linear Eddy Viscosity Models (LEVMs) are used in the positively buoyant wall jet model for discharging of heated waste including: standard k-e, RNG k-e, realizable k-e and SST k-ω turbulence models. It was found that RNG k-e, and realizable k-e turbulence models performed better among the four models chosen. Then, in the next step, numerical simulations of 30˚ and 45˚ inclined dense turbulent jets in stationary ambient water have been conducted. These two angles are examined in this study due to lower terminal rise height for 30˚ and 45˚, which is very important for discharges of effluent in shallow waters compared to higher angles. Five Reynolds-Averaged Navier-Stokes (RANS) turbulence models are applied to evaluate the accuracy of CFD predictions. These models include two LEVMs: RNG k-e, and realizable k-e; one Nonlinear Eddy Viscosity Model (NLEVM): Nonlinear k-e; and two Reynolds Stress Models (RSMs): LRR and Launder-Gibson. It has been observed that the LRR turbulence model as well as the realizable k-e model predict the flow more accurately among the various turbulence models studied herein.