Elliptical Liquid Jets Research Articles

Numerical investigation on spray and flow field characteristics of elliptical nozzle in supersonic crossflow

ABSTRACT It has been suggested that using an elliptical nozzle could enhance the atomization and mixture quality. In order to explore the elliptical liquid jet on spray and flow field characteristics in supersonic airflow, the VOF-Spray one-way coupling model was adopted to study the nozzle exit patterns, size, and velocity distribution of droplets. The research also compared the flow field characteristics in Mach 2.85 air crossflow under the application of different orifices. The numerical results showed that elliptical 4 nozzle (Aspect ratio of 4) had better flow performance than circular nozzle. The cavitation area and turbulent disturbance of elliptical 4 nozzle were mainly concentrated in the major axis direction. The elliptical 4 jet always had a lower penetration depth than circular jet. At the flow range of 0 ~ 50 mm, the penetration depth of elliptical 4 jet is roughly 12% less than that of circular jet. Another finding was that the spanwise extension range of elliptical 4 spray was larger than the circular spray. The spanwise extension range of elliptical 4 spray increased by about 19.4% at most in the flow range of 0 ~ 50 mm. Additionally, the elliptical 4 spray had the smallest Santer Mean Diameter (SMD). The elliptical 4 jet had a 2.9% smaller Santer Mean Diameter than the circular jet. Due to the greater windward surface area of the elliptical 4 orifice, the gas streamwise velocity near the bottom wall was reduced. A reverse vortex pair with distinct characteristics could be observed under the application of elliptical 4 orifice. Furthermore, compared with the circular orifice, the shock wave angle generated by elliptical 4 orifice reduced by 9.7%, and the total pressure recovery coefficient rose by 2.3%.

AERATED CIRCULAR AND ELLIPTICAL LIQUID JETS IN A GASEOUS CROSSFLOW

In this study, the atomization of an effervescent atomizer with an elliptical and circular orifice was investigated experimentally in the gaseous crossflow. The shadowgraph technique was used to visualize the near field of the spray atomization. To measure the spray penetration height in crossflow, image processing was performed on the shadowgraph images based on two different approaches: (i) a threshold analysis of average spray images and (ii) standard deviation images of spray. By comparing these two approaches, it is found that the penetration heights obtained from the standard deviation images were much higher since these images were able to capture small droplets more accurately. Moreover, based on the standard deviation images of spray, an empirical correlation for the spray penetration height was developed as a function of gas-liquid mass flowrate ratio, liquid-air momentum flux ratio, orifice aspect ratio, and downstream location. The laser diffraction technique was used to analyze the particle size of the aerated elliptical and aerated circular jets in a gaseous crossflow. For each orifice shape, the effect of gas-liquid ratio and downstream location on the Sauter mean diameter (SMD) was studied. The results show that the aerated circular jet penetrates higher into the gaseous crossflow than the aerated elliptical jet. Besides, the aerated circular jet in crossflow mainly generates smaller drop sizes compared to the aerated elliptical jet.

An Artificial Neural Network for the Prediction of Penetration Height of Aerated Elliptical Liquid Jets in Gaseous Crossflows

An Artificial Neural Network for the Prediction of Penetration Height of Aerated Elliptical Liquid Jets in Gaseous Crossflows

Dynamic mode decomposition of elliptical liquid jets in crossflow

The dynamics of round and elliptical liquid jets in subsonic crossflow was studied using high-speed imaging technique. The experiments were performed at constant gaseous Weber number and liquid–gas momentum flux ratios of 6.45 and 17.87, respectively, with orifices of different aspect ratios (AR) having an equivalent diameter of 0.43 mm. All of the cases were carried out inside an open-loop subsonic wind tunnel with a test section of 100 mm × 100 mm × 750 mm. For each case, dynamic modes were generated directly from the snapshots using a variant of the Arnoldi method known as the dynamic mode decomposition (DMD). The DMD results indicate that elliptical liquid jets have more small-scaled patterns with higher frequencies compared with the round liquid jets. As the first attempt to investigate the dynamics of elliptical liquid jets in crossflow, this study captures the dominant spatiotemporal structures. We also found that the orifice AR can significantly alter the jet wavelengths. The data from this study contribute to understanding the behavior of elliptical liquid jets exposed to gas crossflow in an enhanced capillary breakup regime.

Simulation of Elliptical Liquid Jet Primary Breakup In Supersonic Crossflow

The study of elliptical liquid jets in supersonic flow in a Mach 2.0 is performed numerically. The primary breakup process of the elliptical liquid jet is simulated for a Weber number 223, liquid/gas flux momentum 4.0. The aspect ratios of elliptical geometries are set to be 0.25, 0.5, 1, 2, and 5. The results show a remarkable difference in liquid jet disintegration morphology at different aspect ratios. Under supersonic crossflow conditions, the elliptical liquid jet shows more breakup characteristics than the round liquid jet. As the aspect ratio grows, the penetration depth decreases. The elliptical liquid jet with AR=0.25 has the largest penetration depth in all cases. Moreover, the round jet has a maximum spreading angle of 50.2°. The changing trends of the column breakup length both x direction and y direction are similar. The elliptical jet at a lower aspect ratio has a shorter breakup length due to the narrower windward area. The liquid jet has a pair of larger horseshoe vortex structure and a wider wake region at a higher aspect ratio. Two pairs of reversal vortex pairs with obvious characteristics can be observed in all the simulations.

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.

Laser Fragmentation Synthesis of Colloidal Bismuth Ferrite Particles.

Laser fragmentation of colloidal submicron-sized bismuth ferrite particles was performed by irradiating a liquid jet to synthesize bismuth ferrite nanoparticles. This treatment achieved a size reduction from 450 nm to below 10 nm. A circular and an elliptical fluid jet were compared to control the energy distribution within the fluid jet and thereby the product size distribution and educt decomposition. The resulting colloids were analysed via UV-VIS, XRD and TEM. All methods were used to gain information on size distribution, material morphology and composition. It was found that using an elliptical liquid jet during the laser fragmentation leads to a slightly smaller and narrower size distribution of the resulting product compared to the circular jet.

Comparative study on interfacial oscillations of rectangular and elliptical liquid jets

The instability characteristics and flow structures of water jets injected from rectangular and elliptical nozzles with aspect ratios varying from 2 to 6 were experimentally studied and compared. Shadowgraph technique was employed for flow visualization, and structures on the liquid jet surface were captured using high speed photography. It was found that disturbances originating from the nozzle geometry initially perturbed the liquid column, and then, at high jet velocities, disturbances generated within the flow dominated the jet surface. It was also found that rectangular nozzles introduced more disturbances into the flow than the elliptical ones. The characteristic parameters of axis-switching phenomenon including wavelength, frequency, and amplitude were measured and compared. Axis-switching wavelength was found to increase linearly with Weber number. Also, the wavelengths of rectangular jets were longer than the elliptical jets. Further, the frequency of axis-switching was shown to be reduced with increase of both Weber number and aspect ratio. It was observed that the axis-switching amplitude increased monotonically, reached a peak, and then decreased gradually. It was also found that the axis-switching amplitude varied with Weber number. At lower values of Weber number, the rectangular nozzles had higher amplitude than the elliptical nozzles. However, at higher values of Weber number, this relation was reversed, and the elliptical nozzles had the higher axis-switching amplitudes. This reversal Weber number decreased with the orifice aspect ratio. The reversal Weber number for aspect ratio of 4 was about 289, and it had decreased to 144 for the aspect ratio of 6.

Wavelength and frequency of axis-switching phenomenon formed over rectangular and elliptical liquid jets

A theoretical and experimental study was performed to investigate the wavelength and frequency of axis-switching oscillations established over rectangular and elliptical liquid jets. Several injectors with aspect ratios ranging from 2 to 6 were manufactured for both rectangular and elliptical shapes. Shadowgraph technique was used for flow visualization and high speed photography was employed to capture the flow physics of the liquid jets. The theoretical model developed by Tadjfar and Jaberi (2019) was rewritten by looking at frequency analogous to the previous one for wavelength. The model rewrote the Rayleigh's classical analysis in terms of three segments identifying the influence of shape, aspect ratio, and Weber number. This model was modified to improve predictive accuracy by adding a correction term in terms of powers of aspect ratio. This time, instead of a constant power, a logarithmic function was used to evaluate the coefficients. The modified model improved the predictive accuracy of Rayleigh's model significantly. The results were analyzed from the viewpoint of frequency and wavelength.

Effect of Orifice Geometry on Column Trajectories of Liquid Jets in Crossflows

Effects of orifice geometry on liquid column trajectories of liquid jets in subsonic crossflows were experimentally studied. One circular and four elliptical plain-orifice injectors with different aspect ratios of 1/3 to 3, were designed and utilized. By changing the injection pressure drop from 1 bar to 6 bar with an increment of 1 bar, and thus the liquid–air momentum flux ratio from 15 to 106, back-lit spray photographs of liquid jets in crossflows were taken and then analyzed using an in-house code to detect the upper boundary and centerline of the liquid jet before the breakup point. Analytical liquid column trajectories for circular and elliptical liquid jets were derived through simple assumptions and compared with present experimental data. It was found that the aspect ratio affected the difference between the analytical drag coefficient and the experimental one. Novel empirical equations for liquid column trajectories of circular and elliptical liquid jets in crossflows were suggested as a function of equivalent orifice diameter, liquid–air momentum flux ratio and aspect ratio. The results showed that the present empirical equation for the circular orifice injector could be reasonably applied to the elliptical orifice injectors when the aspect ratio was below one.

Breakup of elliptical liquid jets in gaseous crossflows at low Weber numbers

Breakup of circular and elliptical liquid jets in subsonic gaseous crossflows is experimentally studied using shadowgraph technique. The experiments are performed at gaseous Weber numbers less than 15, the liquid-to-gas momentum flux ratio between 50 and 320, and the orifice aspect ratio between 0.22 and 4.47. It is found that in addition to the momentum flux ratio, the orifice aspect ratio can change the liquid penetration height significantly. For a fixed momentum flux ratio, the penetration of elliptical jets is less than that of circular jet. Moreover, for a given momentum flux ratio and Weber number, the column breakup location of elliptical jets is earlier than that of circular jet. Empirical correlations for the penetration height as well as the column breakup location of circular and elliptical jets are developed in this study.

Penetration of Elliptical Liquid Jets in Low-Speed Crossflow

Trajectory and penetration of elliptical liquid jets emerged into a low-speed crossflow of air are studied. The jets are introduced to the crossflow at different momentum ratios ranging from 1 to 300. The images are analyzed to obtain the trajectories of the outer boundary of the jets for two different aspect ratios. An empirical correlation is proposed for the present injector geometries and for the range of momentum ratio, Weber, and Reynolds numbers used in this study. Finally, a theoretical model for the trajectory of the liquid column for an initially elliptical liquid emerging into a crossflow is presented, and the associated drag coefficients are obtained for a precise trajectory prediction.

Characteristics of Sheet Formed by Collision of Two Elliptical Jets at Short Impact Distance

The research on characteristics of impinging jet has a long history and focuses mainly on the circular jets, whereas the impingement of noncircular jets, such as elliptical jets, receives much less attention. This paper investigated liquid sheet resulting from the oblique collision of two elliptical jets at short impact distance. The elliptical liquid jets contract and collide obliquely at impact point, forming a sheet in the form of a leaf bounded by a thicker rim. An improved theoretical model, taking jet contraction into account, for two elliptical impinging jets is established. The sheet features are obtained by combining the conservation equations between the liquid jet and sheet with the force balance equations of the sheet rim. The calculated sheet shapes are compared with the experiments, and the results show good agreement. The experimental results also indicate that the liquid sheet formed by elliptical jets tends to be larger and more unstable than that formed by circular jets. Based on the model, the effects of axial ratio and impact distance on the sheet characteristics, such as sheet shape and thickness, are also studied.

Experimental study of elliptical jet from sub to supercritical conditions

The jet mixing at supercritical conditions involves fluid dynamics as well as thermodynamic phenomena. All the jet mixing studies at critical conditions to the present date have focused only on axisymmetric jets. When the liquid jet is injected into supercritical environment, the thermodynamic transition could be well understood by considering one of the important fluid properties such as surface tension since it decides the existence of distinct boundary between the liquid and gaseous phase. It is well known that an elliptical liquid jet undergoes axis-switching phenomena under atmospheric conditions due to the presence of surface tension. The experimental investigations were carried out with low speed elliptical jet under supercritical condition. Investigation of the binary component system with fluoroketone jet and N2 gas as environment shows that the surface tension force dominates for a large downstream distance, indicating delayed thermodynamic transition. The increase in pressure to critical state at supercritical temperature is found to expedite the thermodynamic transition. The ligament like structures has been observed rather than droplets for supercritical pressures. However, for the single component system with fluoroketone jet and fluoroketone environment shows that the jet disintegrates into droplets as it is subjected to the chamber conditions even for the subcritical pressures and no axis switching phenomenon is observed. For a single component system, as the pressure is increased to critical state, the liquid jet exhibits gas-gas like mixing behavior and that too without exhibiting axis-switching behavior.

Numerical Simulation of the Breakup of Elliptical Liquid Jet in Still Air

The numerical simulation of liquid jets ejecting from a set of elliptical orifices with different aspect ratios between 1 (circular) and 3.85 is performed for several Weber numbers, ranging from 15 to 330. The axis-switching phenomenon and breakup length of the jets are characterized by means of a volume of fluid (VOF) method, together with a dynamic mesh refinement model. This three-dimensional simulation is compared with a recent experimental work and the results agree well. It is concluded that for Weber numbers ranging from 15 to 100, by increasing the Weber number, the breakup length of the liquid jet increases, reaches a peak, and then decreases suddenly.

Flow and breakup characteristics of elliptical liquid jets

This paper presents the results of an experimental study on liquid jets discharging from elliptical orifices into still ambient air. The experiments were conducted with a set of elliptical orifices of approximately same area of cross section but varying orifice aspect ratio using water and water–glycerol mixture as experimental fluids. The flow behavior of liquid jets was analyzed using their photographs captured by an imaging system. The measurements obtained for the elliptical liquid jets were compared with the circular liquid jets discharging from a circular orifice of the same area of cross section. Elliptical geometry of the orifice results in a flow process by which the emanating liquid jet periodically switches its major and minor axes as it flows downstream of the orifice. In this paper, we attempt to characterize the axis-switching process through its wavelength and amplitude. For a given elliptical orifice, the axis-switching process is dominantly seen in a particular range of flow conditions. The effects of the orifice aspect ratio and liquid viscosity on the axis-switching process are revealed through this study. The experimental results on jet breakup show that axis-switching process has a destabilizing effect on elliptical liquid jets within a particular range of flow conditions and it results in shorter breakup lengths compared to the circular jet. The extent to which axis-switching destabilizes the jet is dictated by the viscosity of liquid. An increase in orifice aspect ratio destabilizes elliptical liquid jets with low viscosity like water; however, this behavior seems to get obscured in water–glycerol mixture elliptical jets due to high viscosity.

BREAKUP OF LIQUID JETS EMANATING FROM ELLIPTICAL ORIFICES AT LOW FLOW CONDITIONS

This article presents experimental results on the breakup behavior of liquid jets emanating from elliptical orifices with different orifice aspect ratios. The experiments were carried out in the range of mean jet velocity 0−5 m/s, using water as the working fluid; the liquid jets were injected vertically downward in still, ambient air. Photographic methods were employed to analyze the breakup characteristics of the liquid jets. The breakup curves of the elliptical orifice jets are compared with those of circular orifices with the same exit area as the elliptical orifices. The comparison shows that the liquid jets emanating from the elliptical orifice are less stable than jets from the circular orifice in a particular range of flow conditions corresponding to a √We range of 2−20. We attribute this enhanced instability of the elliptical jet to the axis-switching process occurring in this √We regime, a phenomenon by which the elliptical jet interchanges major and minor axes periodically as the jet flows downstream. The breakup process of the elliptical jet resembles that of the circular jet below this range of flow conditions, and their breakup curves coincide. Above this range, the elliptical liquid jets exhibit different flow behavior from the circular jet, although their breakup curves coincide again.