Breakup Of Liquid Jet Research Articles

Numerical simulation of kerosene jet in crossflow atomization and evaporation under the elevated pressure and oscillating air-flow condition

The liquid jet penetration, breakup, and spray evaporation in crossflows, which find their importance in aeroegines, are investigated in the steady and oscillating air-crossflows using detailed numerical simulation to improve the understanding of the influence of the inflow oscillation that is commonly caused by the combustion instability on this complex process. To clarify the oscillation effects on jet atomization, the crossflow multimode breakup is considered, incorporating its unique characteristics of holding two different breakup behaviors, i.e., shear breakup and bag breakup. The oscillation frequency is set to be 500 Hz according to previous research on combustion instability. The results show that the liquid jet trajectory under steady air-flow condition is in good agreement with the analytical solution and experimental correlation, around which the oscillating cases present a reasonable breakup behavior. The vortex morphology behind the liquid jet is found to largely affect the droplets evaporation and their downstream delivery. Moreover, the oscillating air inflow condition shows an enhanced atomization and evaporation property, producing the smaller Sauter mean diameter (SMD) and higher fuel vapor distribution at the leeward downstream region. This behavior of atomized spray in the oscillating crossflow suggests that the combustion instability could impose a significant effect on the subsequent spray combustion process.

SIMULATION OF AN ANNULAR LIQUID JET WITH A COAXIAL SUPERSONIC GAS JET IN A MEDICAL INHALER

Medical inhalers have been used for the treatment of a wide range of respiratory diseases including COVID-19. In this study, we investigate the annular liquid jet breakup with a coaxial supersonic gas jet using large eddy simulations. This contributes to a further understanding and improvement of medical inhaler designs. The liquid is sucked in by the low pressure as a result of the high velocity gas jet and breaks up due to the interaction with the gas jet. This type of spray nozzle configuration is commonly used in medical inhalers. Two different gas nozzle diameters are studied. The simulated liquid structure is compared with preliminary, qualitative experimental results. The gas jet pressure and radial velocity of the liquid are found to be coupled and the interaction between them plays an important role in formation of the liquid structure. The effect of gas nozzle diameter on flow rate, mean radius of the liquid, and mean radial velocity, as well as its oscillation behavior has been investigated. The power development of dominate frequencies of averaged radial liquid velocity along the flow direction is shown. The growth of the instabilities can be observed from these results.

BEHAVIOR OF CO-FLOW JETS COUPLED WITH A LONGITUDINAL PERTURBATION

In this study, a numerical simulation is used to show the physics of a coupled forced perturbation and liquid jet in the presence of a low-velocity coaxial gas flow. The volume of fluid (VOF) approach is employed to capture the liquid–gas interface. A sinusoidal velocity with a finite frequency and amplitude is applied at the liquid jet inlet to define a forced perturbation. An annular gas flow with a velocity lower than that of the liquid jet is imposed to examine its influence on the liquid jet breakup mechanism. The annular gas flow is modulated by the sinusoidal velocity inlet, and the effect of this flow on the liquid jet breakup mechanism is analyzed. Different ratios of the gas velocity to liquid velocity are studied. The results indicate that the low-velocity gas flow can considerably affect the behavior of the liquid jet, and this effect becomes more significant as the amplitude of the forced perturbation increases.

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.

Rico and the jets: Direct numerical simulations of turbulent liquid jets

This paper is associated with a poster winner of a 2019 American Physical Society's Di- vision of Fluid Dynamics (DFD) Milton van Dyke Award for work presented at the DFD Gallery of Fluid Motion. The original poster is available online at the Gallery of Fluid Motion, https://doi.org/10.1103/APS.DFD.2019.GFM.P0020 The breakup of an interface into a cascade of droplets and their subsequent coalescence is a generic problem of central importance to a large number of industrial settings. Examples of these applications include the atomisation of propellants in engines, the formation of droplets in injectors, mixers, separators, and the generation of droplets in multiphase flow regime transitions [2, 3, 12]. In all of these situations, it is important to predict the evolving droplet size distribution that results from a competition between breakup and coalescence, which are influenced by a range of multi-scale physics; this includes the interaction of turbulence with interfaces, capillarity, viscosity, and gravity. Therefore, it is unsurprising that the breakup of liquid jets during injection (i.e. atomisation) has received great scientific interest [4, 8, 10, 11, 13]. To the best of our knowledge, the transient dynamics of turbulent liquid/liquid systems have not been reported in the literature. Temporal instabilities and the resulting spatio-temporal interfacial structures are predicted by solving the full three-dimensional two-phase Navier-Stokes system in the context of a hybrid front-tracking/level-set method [14-16].

Evaluation of breakup models for liquid side jets in supersonic cross flows

In this study, numerical simulations of the interaction between supersonic crossflow and a side liquid jet were performed. The processes of the liquid jet breakup, flow separation and shock waves resulting from the interaction of the gas flows and liquid droplets were predicted. In the numerical simulation, a two-way coupling Eulerian-Lagrangian method was used. The two-dimensional unsteady compressible Navier-Stokes Equations were solved based on the MUSCL type (Monotone Upstream-Centred Scheme for Conservation Laws) spatial differencing coupling with Roe-type flux-difference splitting and a third-order accurate Runge-Kutta method for time-splitting. The atomization of liquid droplets was simulated using the combined KH-RT breakup model. The modified breakup model considered both the interface instability and the sudden deformation of a liquid spray induced by the compressible flows. Shock waves, recirculation zones and breakup processes of droplet particles were captured. The predicted droplet distributions at various operating conditions were discussed. Satisfied agreement between simulations and measurements is shown in the current work.

An analysis of surface breakup induced by laser-generated cavitation bubbles in a turbulent liquid jet

The breakup of turbulent liquid jets by cavitation bubbles was investigated by artificially introducing them by focusing laser light into the jet. The induced surface deformations and ejected liquid structures were characterized using shadowgraphy with a high-speed video camera. The flow velocity of the liquid jets, which were ejected from a 6 mm nozzle, was varied by adjusting the injection pressure from 1 to 5 bar. Deionized water and a dipropylene glycol–water mixture were used to compare the breakup of liquid jets with different surface tension and viscosity. Surface deformation and breakup were found to occur in two stages. One was early breakup of liquid strings into tiny droplets. This was followed by the formation of a larger structure separating into ligaments and larger drops. Averaged time-resolved one-dimensional plots were introduced and implemented to analyze breakup statistically, to address the problem of shot-to-shot variations in the breakup due to the turbulent condition of the jets. Bubble-induced breakup could easily be distinguished from spontaneous breakup with this method. Both the position of bubble formation and the injection pressure had an influence on the scale of the breakup. The deformation of the jet surface was highly affected by shear. The structure of the deformation became less intact when the surface tension was lower. The sizes of the drops produced during the second stage of breakup were analyzed. The bubble-induced breakup produced smaller drops than the spontaneous breakup at lower injection pressure. As expected, lower surface tension favored droplet detachment and smaller sized drops.Graphic abstract

Fire Water Monitor Trajectories Based on Turbulence Breakup Model

Abstract Fire remains one of the most pervasive threats to public safety and social development in real life. Fire water monitors have been used as tools for ending the fire all the time. The impact point accuracy of the water jet and the accurate prediction of the water jet trajectory have a significant effect on the efficiency of fire extinction. The quadratic drag model is selected on the basis of the analysis of the mechanical model of fluidic control volume considering the change of the cross-sectional area caused by the velocity and breakup of the water jet. The change of diameter and area of the droplet are also discussed, based on the theory of liquid jet breakup, to build a dynamic breakup model of air resistance and broken jet. The water jet simulations are performed on two different scales by researching several main performance parameters, such as discharge angle and initial velocity, which can affect the jet trajectory of fire water monitor. The influences of various parameters on the jet trajectory are summarized through the simulations of two kinds of water jet experimental data, and an accurate prediction of the jet trajectory of fire water monitor is realized.

Liquid jet breakup and spray formation with annular swirl air

Spray formation is important for liquid fuel combustion from the perspective of emissions and sustaining combustion. Employing swirl flow increases turbulent intensity, which leads to a much-desired outcome for sprays in a reduction of the jet breakup length, better air-fuel mixing and vaporization characteristics, and stabilizes the combustion operation. The present investigation endeavors to characterize the near field spray developing region of a swirl airblast atomizer. The high-speed digital imaging system is employed to record the unsteady dynamics when the liquid jet breaks to form mono-disperse or poly-disperse drop size distribution depending upon the atomizing air to liquid jet momentum ratio. The coherent spatial nature of the atomization process is identified using Proper Orthogonal Decomposition (POD) of acquired high-speed images of the spray in the near field. The simultaneous droplet size and velocities (axial, radial, and tangential) are measured through Phase Doppler Particle Analyzer (PDPA) technique to quantify the effect of the flow field on spray characteristics in the near field of an atomizer. Joint probability distributions of drop size and velocity along with Weber number distribution provide insight into the spray developing near field region. The spatial variations in the drop size distribution are found to be a function of turbulent Weber number (Wet) and shear Weber number (Wes) distribution. Double Gaussian function representing superimposed distributions for larger and smaller droplets provides the highest confidence fit for both velocity and dropsize distributions throughout the flow field. The volume-averaged statistics are proposed for a better description of the actual spray quality.

Spray and mixing characteristics of liquid jet in a tubular gas–liquid atomization mixer

For the design and optimization of a tubular gas–liquid atomization mixer, the atomization and mixing characteristics of liquid jet breakup in the limited tube space is a key problem. In this study, the primary breakup process of liquid jet column was analyzed by high-speed camera, then the droplet size and velocity distribution of atomized droplets were measured by Phase-Doppler anemometry (PDA). The hydrodynamic characteristics of gas flow in tubular gas–liquid atomization mixer were analyzed by computational fluid dynamics (CFD) numerical simulation. The results indicate that the liquid flow rate has little effect on the atomization droplet size and atomization pressure drop, and the gas flow rate is the main influence parameter. Under all experimental gas flow conditions, the liquid jet column undergoes a primary breakup process, forming larger liquid blocks and droplets. When the gas flow rate ( Q g ) is less than 127 m 3 ·h −1 , the secondary breakup of large liquid blocks and droplets does not occur in venturi throat region. The Sauter mean diameter (SMD) of droplets measured at the outlet is more than 140 μm, and the distribution is uneven. When Q g > 127 m 3 ·h −1 , the large liquid blocks and droplets have secondary breakup process at the throat region. The SMD of droplets measured at the outlet is less than 140 μm, and the distribution is uniform. When 127 < Q g < 162 m 3 ·h −1 , the secondary breakup mode of droplets is bag breakup or pouch breakup. When 181 < Q g < 216 m 3 ·h −1 , the secondary breakup mode of droplets is shear breakup or catastrophic breakup. In order to ensure efficient atomization and mixing, the throat gas velocity of the tubular atomization mixer should be designed to be about 51 m·s −1 under the lowest operating flow rate. The pressure drop of the tubular atomization mixer increases linearly with the square of gas velocity, and the resistance coefficient is about 2.55 in single-phase flow condition and 2.73 in gas–liquid atomization condition. The breakup morphologies of liquid jet with different liquid and gas flow rates are photographed by a high-speed camera respectively. The liquid jet column swings and breaks up into large droplets and liquid blocks in the air flow. When flow through the Venturi throat, these large droplets and liquid blocks break up into smaller droplets. The particle size and velocity distribution of atomized droplets were measured by Phase-Doppler anemometry (PDA). Under the same gas flow rate condition, the droplet sizes at different measured points are basically the same, and the droplet size decreases gradually with the increase of gas velocity. With the increase of gas velocity, the droplet size distribution of each measured point is closer to a straight line, and the uniformity of atomized droplet distribution in the tube is better. With the value of the gas velocity 72 m 3 ·h −1 , the average droplet size is about 200 μm, and with the value of the gas velocity 216 m 3 ·h −1 , the average droplet size is about 50 μm. • Experiments were performed on droplet size and velocity in tubular atomizing mixer. • Breakup morphologies of liquid jet under different flow conditions were obtained. • The relationship between gas flow rate and droplet size was obtained. • Gas–liquid atomizing and mixing characteristics in tubular mixer were analyzed.

Breakup Processes and Droplet Characteristics of Liquid Jets Injected into Low-Speed Air Crossflow

The breakup processes and droplet characteristics of a liquid jet injected into a low-speed air crossflow in the finite space were experimentally investigated. The liquid jet breakup processes were recorded by high-speed photography, and phase-Doppler anemometry (PDA) was employed to measure the droplet sizes and droplet velocities. Through the instantaneous image observation, the liquid jet breakup mode could be divided into bump breakup, arcade breakup and bag breakup modes, and the experimental regime map of primary breakup processes was summarized. The transition boundaries between different breakup modes were found. The gas Weber number (Weg) could be considered as the most sensitive dimensionless parameter for the breakup mode. There was a Weg transition point, and droplet size distribution was able to change from the oblique-I-type to the C-type with an increase in Weg. The liquid jet Weber number (Wej) had little effect on droplet size distribution, and droplet size was in the range of 50–150 μm. If Weg &gt; 7.55, the atomization efficiency would be very considerable. Droplet velocity increased significantly with an increase in Weg of the air crossflow, but the change in droplet velocity was not obvious with the increase in Wej. Weg had a decisive effect on the droplet velocity distribution in the outlet section of test tube.

Empirical correlation for spray half cone angle in plain-jet airblast atomizers

Plain-jet airblast atomizers are widely used in industrial applications. The literature contains numerous papers on Sauter mean diameter, however, there is no estimation method available for spray cone angle, SCA, which derivation is the primary goal of this study. Four distinct, practical model liquids were analyzed: distilled water, diesel oil, light heating oil, and crude rapeseed oil. The atomizing pressure and liquid preheating temperature were varied in the range of 0.3–2.4 bar and 25–85 °C, respectively. This latter parameter enabled a wide and continuous liquid kinematic viscosity investigation range of 0.33–44.2 mm2/s. The resulting sprays were imaged at various shutter speeds for proper edge detection. An adaptive thresholding algorithm was developed in Matlab software environment to calculate SCA. The methodology is discussed in detail to facilitate the re-implementation of this technique since there is no generally accepted method for SCA measurement. SCA inversely varied with liquid density and followed a power law with the air-to-liquid mass flow ratio; however, the derived expression also performed well by replacing air-to-liquid mass flow ratio by either Mach number or momentum flux ratio. A simple empirical equation was derived, which allows the estimation of SCA of airblast atomization in a wide parameter range within a 3.5% deviation. The measured results were evaluated in the light of high-speed camera images in the vicinity of the nozzle; it was found that increased liquid jet breakup length decreases SCA while intense ligament formation increases it.

Dynamic analysis of the primary breakup of an annular energetic liquid jet injecting into a confined space

The Large Eddy Simulation (LES) with the Volume of Fluid (VOF) method was carried out to investigate the primary breakup dynamic mechanism of an annular energetic liquid jet injecting into a confined space. The gas vortex structure and the liquid jet formation were visualized by tracking the evolution of the phase velocity and the interface location, and hence the coalescence process of the goblet-shaped liquid jet from the annular liquid jet was reproduced. Simulation results indicate that the first coalescence is caused by the Rayleigh-Taylor instability, which is generated by the interaction between the liquid jet head and the gas in the confined space. Two kinds of large-scale vortex structure expedite the secondary coalescence and the final goblet-shaped liquid jet form. Cavities are observed on the dense liquid jet column as a result of the coalescence on the upstream. Consequently, the droplet breakup occurs more frequently on the downstream liquid jet under the gas phase disturbance. The viscous shear is created by the aerodynamic interaction, and the regular fish-scale structure is presented under the Kelvin-Helmholtz instability, which promotes the bulge surface to break into droplets. The research reveals the dynamic mechanism of the annular energetic liquid jet structural destabilization observed in the previous experiments. The combination of the structural instability and the surface instability facilitate the primary breakup of the annular energetic liquid jet, which is beneficial to improve the atomization and the combustion performance.

Numerical Modeling of Instability and Breakup of Elliptical Liquid Jets

Numerical simulations are performed to provide an in-depth insight into the effect of instabilities on liquid jets discharging from elliptical orifices. The axis-switching phenomenon and breakup are simulated and characterized under the effect of disturbances imposed at the nozzle exit. The simulations are based on the volume of fluid approach and an adaptive meshing. A range of orifice aspect ratios from 1 to 4 at the Rayleigh breakup regime is considered. The evolution of the jet cross section and axis switching under the influence of disturbances is compared with that of nonperturbed elliptical jets. It is found that the axis-switching repetition and breakup length exponentially decrease with the initial amplitude of disturbances. For a fixed amplitude, the optimum wavenumber responsible for minimum breakup length is observed to be dependent on ellipticity of the orifice. Moreover, it is found that the form of final breakup leads to elimination of the satellite droplets at the optimum wavenumbers, while the droplet size decreases and becomes more uniform.

Axis-switching and breakup of rectangular liquid jets

The behavior of low-speed liquid jets emerging from rectangular orifices into a quiescent air is studied numerically. After ejection, the rectangular cross-section transforms into an elliptical form along the jet and while axis-switching includes elliptical cross-sections only, the rectangular shape never establishes again. The optimum wavenumber, corresponding to the most dominant wave, is found to be greater in orifices with higher aspect ratios and, as a result, breakup length of the jet will be shorter. The breakup length decreases exponentially with the initial amplitude of disturbances. Moreover, it is observed that the form of final breakup leads to elimination of the satellite droplets at the optimum wavenumber with small and uniform main droplets. It is also shown that high-aspect ratio jets have a more extended range of effective disturbances. The results provide an in-depth insight into the effect of instabilities on axis-switching, breakup, and droplet formation.

Effects of Shaping Air on Breakup of Liquid Jet

Effects of Shaping Air on Breakup of Liquid Jet

Nonlinear Evolution and Breakup of the Cavitating Liquid Jet Surrounded by the Rotary Compressible Air.

A nonlinear dispersion relationship has been established to study the surface evolution and breakup of the cavitating liquid jet with cavitation bubbles surrounded by the rotary air, and the built dispersion relationship and its solution are validated by comparing with the results in the reference. The effects of air rotation, fluid compressibility, and bubble volume fraction on jet morphology are investigated mainly. Air rotation changes the dominant mode of perturbation wave on the jet surface, and more uneven corrugated flows are formed at the interface with the increase of gas rotational strength. The fluid compressibility has little impact on jet morphology in the circumferential direction, while it has some impacts on the axial morphology, especially on the arrangement of droplets. Cavitation bubbles will affect the jet morphology, while the effect is smaller than gas rotation. Both swirling gas and fluid compressibility promote the jet breakup, while the influence of compressibility on jet breakup is obviously greater than gas rotation. In addition, the bubble volume fraction will promote the breakup of the cavitating liquid jet; however, this kind of promoting impact decreases with the increase of the cavitation bubble volume fraction.

Liquid jet breakup behind a pylon in supersonic flow

The thin pylon has been found to be one of the most promising hypermixers, offering enhanced mixing of fuel with minimum pressure loss. In the present study, the effect of pylon height and the angled injection on the liquid jet breakup and its effect on atomization in a free stream of Mach 1.71 has been studied experimentally. Acetone is used as the liquid medium to characterize the liquid jet injection in supersonic flow. Acetone is injected into the flow in the transverse direction behind the pylon at different mass flow rates for 3 different pylon geometries and 3 angled injection cases. The height of the pylon is varied (17.32 mm, 10 mm, 6 mm) and the injection angle is such that it impinges against the pylon wall at three different angles of 30°, 45° and 60° while maintaining the other geometrical features to be the same. The study includes Schlieren imaging to find the effect of liquid injection and Pylon on the compressible flow field, and Shadowgraphy visualization was employed to evaluate the jet disintegration and atomization; Mie Scattering visualization techniques were used for evaluating the lateral spread of liquid jet spray. Mathematical techniques such as temporal variance, POD and DMD are used to analyze the temporal behavior of the jet spread. It is observed that the pylon height not only increases the penetration height but also has a significant effect on the jet breakup and atomization. The shear layer also plays a major role in jet atomization and penetration height. Angled injection case was observed to perform better than transverse injection in terms of penetration height and jet spread.

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.

Liquid jet penetration and breakup in a free supersonic gas jet

The interaction of a coherent liquid jet with a free supersonic gas jet is of importance in cooling high-temperature exhaust plumes generated by ground rocket tests. Further, the associated phenomena are distinct from the well-studied jet in supersonic crossflow due to the unbounded nature of the gas jet, its shock train structure, and the relative sizes of the two jets. This work utilizes non-intrusive diagnostics including focused color Schlieren, high-speed diffused backlit imaging, and volume-illuminated imaging to study the interaction process of a high Reynolds number water jet with a free supersonic air jet. The effect of the water jet on the shock train structure and its dependence on water injection location and pressure are studied. The ensuing water jet breakup mode is investigated and found to exhibit distinguishing characteristics from known breakup modes observed at high Reynolds and gas Weber numbers. Finally, the water jet penetration height is quantified, and the ability of existing correlations from the literature to predict the penetration height are investigated.