Breakup Process Of Liquid Jet Research Articles

Numerical investigation of particle dispersion and collision in a liquid jet flow

A numerical simulation with the Eulerian–Lagrangian point-particle approach is used to study the dispersion of nanoparticles in liquid jet flows. The volume of fluid method is used to simulate the motion of the gas–liquid interface. The particle motion is resolved by the Lagrangian point-particle model, and the collisions among particles are considered. According to the simulation results, the liquid jet atomization process can be divided into four different periods. Moreover, the nanoparticles lead to an increase in the liquid density and viscosity. The influence of the particle motion on the liquid jet breakup process is discussed. The simulation results show that the collisions would restrain particle dispersion. However, the motions and collisions of the particles would help the breakup of the liquid jet.

Jet flapping and its effect on flame oscillations in the SPP1980 SpraySyn burner

The present research work aims in investigating the large-scale jet flapping instability during the primary breakup process and its effects on the liquid shedding and the resulting flame. For this purpose, a modified coaxial burner is operated over wide range of flow conditions with different liquids in the central passage. Time-resolved images of the liquid jet breakup process and the resulting flame during spray combustion are captured. A Proper orthogonal decomposition (POD) technique is used to investigate the jet flapping and calculate the time-scale corresponding to this mode of instability. Fast-Fourier Transform (FFT) analysis is performed over the average intensity of the interrogation window in an image ensemble to measure the time-scale corresponding to liquid shedding and flame fluctuations. A strong dependence of the frequency corresponding to jet flapping, liquid shedding and flame fluctuations is observed with respect to the dispersion gas velocity. Jet flapping indicates a strong influence on the liquid shedding from the liquid jet, which then influences the resulting flame in the downstream region of the burner.

Fragmentation and atomization characteristics of near-orifice liquid jet under transverse gas film

In order to understand the fragmentation and atomization characteristics of the liquid jet in transverse gas film, a pintle injection element using air and water as simulants is designed. The two-phase flow large eddy simulation and backlight imaging are used to study the liquid-jet breakup process and spray-field dynamic characteristics in the nearorifice area of pinte injection element under the atmospheric environment. The primary fragmentation process of the liquid jet dominated by surface wave is obtained by large eddy simulation, which reveals the establishment process of the spray field in near-orifice area of the gas-liquid pintle injector. After the subsonic airflow leaves the slit, it expands and accelerates into supersonic state. Then the deceleration and pressurization phenomenon occurs once the supersonic airflow passes through the detached bow shock upstream of the liquid jet. The liquid jet bends downstream due to the difference in pressure between upstream and downstream, and the Rayleigh-Taylor (R-T) unstable surface wave appears on the jet windward surface. As the surface wave develops, the penetration of the wave trough by airflow causes the continuous liquid jet to fragment. Proper orthogonal decomposition (POD) method can effectively reconstruct spray snapshot. The POD mode shows that the low-frequency spray oscillation in near-orifice area is caused by the overall expansion/contraction process of the spray field, while the high-frequency one is due to the “impact wave” movement of the liquid block or liquid mist group on the windward side. The latter is produced by the R-T unstable surface wave before the jet breakup, and can be categorized as traveling wave structure. The dimensionless traveling wave wavelength has a power-law relationship with Weber number.

Coupled lattice Boltzmann-large eddy simulation model for three-dimensional multiphase flows at large density ratio and high Reynolds number.

A coupled lattice Boltzmann-large eddy simulation model is developed for modeling three-dimensional multiphase flows at large density ratios and high Reynolds numbers. In the framework of the lattice Boltzmann method, the model is proposed based on the standard Smagorinsky subgrid-scale approach, and a reconstructed multiple-relaxation-time collision operator is adopted. The conservative Allen-Cahn equation and Navier-Stokes equations are solved through the lattice Boltzmann discretization scheme for the interface tracking and velocity field evolution, respectively. Relevant benchmark cases are carried out to validate the performance of this model in simulating multiphase flows at a large density ratio and a high Reynolds number, including a stationary droplet, the process of spinodal decomposition, the Rayleigh-Taylor instability, the phenomenon of a droplet splashing on a thin liquid film, and the liquid jet breakup process. The maximum values of density ratio and Re number are 1000 and 10 240, respectively. The capability and reliability of the proposed model have been demonstrated by the good agreement between simulation results and the analytical solutions or the previously available results.

Breakup process of liquid jet in gas film

In order to study the breakup process of liquid jet in gas film, the backlit photography technique and the VOF TO DPM method are used for experimental and simulation research respectively. Water and air are used as simulant media. Grid adaptive technology is used to refine the gas-liquid interface grid and improve the capture accuracy of the gas-liquid interface. The results show that there are two main breakup processes of liquid jet in gas film: column breakup and surface breakup. The local high-pressure zone in front of the liquid jet makes the jet have a large normal velocity gradient, which causes R-T instability. The surface wave that is generated by the R-T instability is mainly responsible for the liquid column breakup. When the thin liquid film reaches a column breakup point, the airflow penetrating the trough of the surface wave causes the jet column to break. The tangential velocity gradient is generated when the gas film bypasses the liquid jet surface, which causes K-H instability. The K-H surface waves cause ligaments and droplets to strip from the surface of the liquid jet. The local momentum ratio has an important influence on the breakup process of the liquid jet in gas film. When the local momentum ratio is low, the breakup of liquid jet is dominated by the K-H instability. As the local momentum ratio increases, the breakup of liquid jet is gradually dominated by R-T instability. The local momentum ratio plays an important role in the distribution range of the liquid jet in gas film. When the local momentum ratio is low, the ligaments and droplets caused by the liquid jet are mainly distributed within the range of gas film. As the local momentum ratio increases, part of the ligaments and droplets escape from the range of the gas film. The liquid jet penetrates the gas film when the local momentum ratio is greater than 0.74. The breakup length and the penetration depth are both affected by the local momentum ratio. The breakup length increases with the local momentum ratio increasing. The penetration depth also increases with the local momentum ratio, and the penetration depth increases significantly when the liquid jet penetrates the gas film.

Effects of surface tension and viscosity on liquid jet breakup

The breakup process of liquid jet was explored through visualization using a high-speed camera to develop a prediction model for the impact frequency (the number of droplet passing per unit time). The experiments were conducted for the three jet regimes of Rayleigh, first wind-induced and second wind-induced. The five liquids (water, two ethanol aqueous solutions, and two glycerin aqueous solutions) were used as the test liquids to explore the effects of surface tension and viscosity. Since the droplets were produced due to jet breakup, the impact frequency was zero just downstream of the nozzle and increased asymptotically with an increase in the distance from the nozzle. Thus, auxiliary correlations were developed for the minimum breakup length where the jet breakup is initiated, the maximum breakup length where the jet breakup is completed, and the mean droplet size and the impact frequency in the equilibrium region downstream of the maximum breakup length. Since the correlations were dependent on the flow regime, the boundaries between the three jet regimes were also determined using the present observation results. It was demonstrated that the impact frequencies calculated by the proposed model agree with the experimental data accumulated in this work fairly well in the Rayleigh and second wind-induced regimes, while agreement was deteriorated to some extent in the transition (first wind-induced) regime. For the application to the prediction of splashing rate during coolant leakage in sodium-cooled fast reactors, a simple method to ensure conservative estimation of the impact frequency was also proposed.

Experiment on the Breakup of Liquid Jets in Different Cross-Airflows

The experiment is conducted with a high-speed camera to investigate the breakup processes of liquid jets in uniform, shear-laden, and swirling cross-airflows. The liquid used in the test is water, the nozzle diameter is 2 mm, and the liquid-to-air momentum flux ratio q ranges from 5 to 3408.5. The results indicate that liquid jets break up to form small droplets in the uniform cross-airflow. There is an exponential relation between the broken position and q. In the shear-laden cross-airflow, the penetration depth of the jet is similar to that of the uniform case, both of which increase with the increase of q. When q and the mean Weber number are the same as the uniform case, the penetration depth of the jet increases by 25% when the velocity ratio of the upper and lower inlets is UR=5; the jet penetration depth decreases by 47.2% when the ratio of UR=0.2 and the jet breaks up quickly and the atomization effect will be better. In the swirling cross-airflow, the jet trajectory is similar to the uniform case and also satisfies the exponential property. When the swirl is weak (swirling number SN=0.49), the jet penetration depth increases compared to the uniform case; when the swirl is strong (SN=0.82), the cross-swirling airflow restrains the jet penetration depth.

Effects of inner bubble on liquid jet breakup

In this study, the effects of the bubble on the liquid jet breakup process were investigated using a high-speed camera. The liquid jet containing bubbles revealed a considerable decrease in the breakup length when compared with the water jet without bubbles, which promoted the atomization performance significantly. Theoretical analysis was based on the classical linear stability theory and the equivalence of the initial jet diameter and velocity disturbance amplitude. We deduced a correlation between the breakup length ratio and the diameter of the bubbles, and the theoretical results showed good agreement with our experimental results. Our results also showed that the property of gas affected the breakup process of the liquid jet containing bubbles. The experimental findings indicated that lighter gases could realize a more significant decrease in the breakup length, which could then be attributed to the conservation of momentum of the fluid.

Multiphase simulation of liquid jet breakup using smoothed particle hydrodynamics

This paper deals with numerical modeling of two-phase liquid jet breakup using the smoothed particle hydrodynamics (SPH) method. Simulation of multiphase flows involving fluids with a high-density ratio causes large pressure gradients at the interface and subsequently divergence of numerical solutions. A modified procedure extended by Monaghan and Rafiee is employed to stabilize the sharp interface between the fluids. Various test cases such as Rayleigh–Taylor instability, two-phase still water and air bubble rising in water have been conducted, by which the capability of accurately capturing the physics of multiphase flows is verified. The results of these simulations are in a good agreement with analytical and previous numerical solutions. Finally, the simulation of the breakup process of liquid jet into surrounding air is accomplished. The whole numerical solutions are accomplished for both Wendland and cubic spline kernel functions and Wendland kernel function gave more accurate results. Length of liquid breakup in Rayleigh regime is calculated for various flow conditions such as different Reynolds and Weber numbers. The results of breakup length demonstrate in satisfactory agreement with the experimental correlation. Finally, impinging distance and breakup length of a simple multijet setup are analyzed. The two-jet multijet has a longer breakup length than a three-jet one.

Modeling the disintegration of cavitating turbulent liquid jets using a novel VOF–CIMD approach

In this article, a novel modeling approach capable of simultaneously tracking the events of cavitation, occurring within an injector nozzle, and the liquid jet breakup process, inclusive of spray formation, in the nozzle exterior is presented. A single fluid model, embedded with a Volume-of-Fluid (VOF)-based interface capturing methodology for monitoring the liquid–gas interface dynamics, is supplemented with a vapor transport model for predicting cavitation events triggered within the liquid. While the surface forces due to liquid–gas interfacial instabilities are modeled using a Continuum Surface Force model, a Cavitation-Induced-Momentum-Defect (CIMD) correction approach is employed to account for the effects of cavitation dynamics within the liquid flow. Liquid turbulence is modeled using the well-known RNG k–ε model inclusive of new source terms due to cavitation-induced turbulent kinetic energy production and dissipation. The combined VOF–CIMD methodology is validated by examining the effects of cavitation on the disintegration of turbulent planar liquid jets exiting a two-dimensional nozzle. Different flow Reynolds and Cavitation number configurations are tested. The results predicted by the model including those of the transport vapor dynamics and the liquid jet disintegration processes match, both qualitatively and quantitatively, very well with the available experimental data. In comparison with experimental observation, our model predicts different regimes of liquid jet behavior such as wavy jet, spray formation simultaneously with events of developing or super-cavitation. The numerical approach elaborated in this article can be extensively applied in the design and development of efficient spray applicators and other industrial fluidic devices.

Effect of gas stream swirls on the instability of viscous annular liquid jets

A linear temporal instability analysis has been carried out for a viscous annular liquid jet moving in two swirling gas streams of unequal velocities with the gas stream swirling motion represented by free-vortex rotation. It is found that two modes of unstable surface waves exist, the para-sinuous and para-varicose mode. The results of the two limiting flow situations, which are a cylindrical liquid jet in a swirling gas stream and a swirling gas jet in a liquid stream, indicate that their instabilities are associated with the para-varicose mode on the outer interface and para-sinuous mode on the inner interface of the annular liquid jet, respectively. It is shown that the centripetal force induced by the inner gas stream rotation is destabilizing and enhances the jet instability, while the centripetal force produced by the outer gas stream rotation is stabilizing and reduces the instability of annular liquid jets. It is interesting to find that for a para-varicose mode an increase in the outer gas rotation not only reduces the upper cut-off wave number, but also increases the lower cut-off wave number, leading to the significant reduction in the unstable wave number range. The stabilizing effect of the outer gas rotation is much more significant for para-varicose mode, and the destabilizing effect of the inner gas rotation is much more influential for para-sinuous mode. In general, the para-sinuous mode has a much larger growth rate and is predominant in the annular liquid jet breakup process. Therefore, increasing the inner gas stream rotation can significantly enhance the breakup of annular liquid jets for practical spray applications.

Breakup Processes of Liquid Jets in Subsonic Crossflows

The breakup processes of liquid jets injected into subsonic air crosse ows were experimentally studied. Test liquids, injector diameters, and air Mach numbers were varied to provide a wide range of jet operation conditions. Results indicate that for larger injection velocity conditions liquid jets penetrate relatively far into the crosse ows and exhibit surface breakup processes before the column breaks. Liquid column trajectories were correlated by liquid/air momentum e ux ratios based on a force analysis of a cylindrical liquid element subjected to an aerodynamic drag force. Drag coefe cients were inferred from the column trajectories and were found to exhibit a weak dependence on liquid viscosity. The heights of the column fracture points were correlated using the time required for an analogous droplet to complete an aerodynamic secondary breakup process. The success of the resulting correlation justie es the assumption that the aerodynamic forces acting on a droplet and those acting on a liquid column have similar effects. This result, combined with the trajectory correlation, leads to the conclusion that the liquid column always breaks at the same streamwise location, in agreement with the present experimental observation.

Characteristics of Liquid Jet Atomization across a High-Speed Airstream. 3rd Report, Breakup Process of Liquid Jet and Internal Structure of Spray.

To elucidate deformation and breakup processes of a liquid jet across an airstream, tomograms of the liquid jet were taken by means of the laser light sheet method. In this method, fluorescent dye, Eosine-Y, was contained in the injected water, and the liquid jet was illuminated by the Nd : YAG laser light sheet. There are two types of atomization mechanisms. In the first mechanism, a horizontal section of the liquid column is distorted into a bow shape, and there exists a cavity without drops behind the liquid column. Small drops are produced at both tips of the bow. The continuous length and the width of the liquid column were measured from the tomograms. In the second mechanism, in which velocities of both the airstream and the injecting liquid are low, the liquid column is distorted in a snakelike shape and drops are produced near the tip of the liquid column.

Observations of breakup processes of liquid jets using real-time X-ray radiography

Observations of breakup processes of liquid jets using real-time X-ray radiography