Liquid Jets In Subsonic Crossflows Research Articles

The breakup and instability structures of liquid jets in subsonic crossflows

The breakup of water and Jet A fuel jets injected transverse into elevated temperature (up to 425 °C), combustion pre-heated, subsonic crossflows was investigated by internally fluorescing the liquid jet column. The fluorescent dye seeded test liquids were illuminated by a pulsed laser light that was transmitted within the injector using a quartz rod light-guide. High-resolution images isolating the intact liquid column from light scattered by the surrounding dense spray facilitated precise measurement of the liquid column breakup position and the size and distribution of windward column instability waves. The injector geometry consisted of a 1 mm circular orifice with an orifice length of 20 mm with a tapered inlet. Liquid jet to gaseous crossflow momentum flux ratios were varied from 6 to 266 and the gas Weber number was varied from 10.7 to 228. Empirical correlations were derived for the liquid column breakup coordinates and breakup time in addition to the average and local maximum instability wavelength and amplitude on the liquid column windward surface. The reported correlations provided key insight into atomization physics and aim to support the quantitative validation of high-fidelity numerical simulations of the liquid jet in subsonic crossflow.

Numerical simulation of primary atomization process of liquid jet in subsonic crossflow

Studies of primary atomization of liquid transverse jets in subsonic crossflow consider surface waves as the main cause of jet fragmentation. The characteristics of surface waves during jet fragmentation have been initially analyzed, but there is a lack of understanding of the mechanism of surface wave generation and development. This paper investigates the primary atomization of liquid transverse jets in subsonic crossflow based on the numerical method of Large Eddy Simulation (LES) with the coupled level set and volume of fluid method (CLSVOF) interface tracking, combined with adaptive mesh encryption techniques, where the liquid phase medium is water. This paper focuses on the fine structure of the primary atomization of the jet column, including the evolution of the jet column and the process of shedding the surface of the jet column, to clarify the physical process of primary fragmentation of the jet. The near-field flow structure and gas–liquid interaction are also analyzed to investigate the mechanism of primary atomization of liquid transverse jets and the mechanism of surface wave generation and development in subsonic flows. The results show that the shear action of gas and liquid leads to the generation of Kelvin–Helmholtz (KH) unstable wave, and KH surface wave dominates the surface breaking of jet column. The extrusion of gas and liquid results in the unstable fluctuation of Rayleigh–Taylor (RT), and the RT surface wave dominates the jet column, and finally the cylindrical fracture occurs. The development trend of RT surface wave is to increase the wavelength along the jet direction. When the wavelength of the RT surface wave develops from 0.12 mm to 1.2 mm, the jet column will be columnar broken at the trough of the last RT wave.

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.

On the trajectory of nonturbulent liquid jets in subsonic crossflows at different density ratios

ABSTRACT Numerical simulations using volume of fluid (VOF) method are performed to study the impact of liquid-to-gas density ratio on the trajectory of nonturbulent liquid jets in gaseous crossflows. In this paper, large eddy simulation (LES) turbulence model is coupled with the VOF method to describe the turbulence effects accurately. In addition, dynamic adaptive mesh refinement method with two refinement levels is applied to refine the size of the cells located at gas-liquid interface. Density ratio is changed from 10 to 5000 while other nondimensional numbers are kept constant. Large density ratios are considered in this paper since they are common in many practical applications such as solution precursor/suspension plasma sprays. Our simulations show that the penetration height, especially in the farfield, increases as the density ratio increases. A general correlation for the jet trajectory, which can be used for a wide range of density ratios, is developed based on our simulation results.

Effects of Orifice Internal Flow on Liquid Jets in Subsonic Crossflows

Effects of Orifice Internal Flow on Liquid Jets in Subsonic Crossflows

Effects of Orifice Internal Flow on Liquid Jets in Subsonic Crossflows

The effects of orifice internal flow on the spray plume characteristics of the liquid jet injected perpendicularly into subsonic crossflows were investigated experimentally. The internal flows are classified into threemodes: steady flow, cavitationflow, andhydraulic flipflow.Thesemodes aremainly determined by the ratio of the injector lengthL to the injector diameter d and by the shape of the orifice internal edge. To study the spray plume characteristics corresponding to each mode, three measurement techniques were applied: mass-flow-rate measurement, direct photography of internal injector orifices, and planar liquid laser-induced fluorescence. From the results of themassflow-rate measurement and direct photography, each mode of orifice internal flow without air crossflow was classified through the discharge coefficient patterns and internal–external flow shape. Steady flow shows no significant change on the flow pattern, and the discharge coefficient increases as the pressure differential increases. However, unsteady flows, including cavitation and hydraulic flip, have strong bubble envelopes due to a sudden reduction of flow passage, and these phenomena affect the discharge coefficient patterns. The penetrations and the width of the liquid spray plume were analyzed using the images obtained from the planar liquid laser-induced fluorescence method, and they were compared with the previous results. The penetrations and width were formulated with the liquid–air momentum flux ratio q and the ratio of the distance from the injector exit to the injector diameter x=d. It is found that the spray plume trajectory is determined by the liquid column diameter of the orifice exit and the liquid–air momentum flux ratio using the jet velocity at the orifice exit. It is also found that it is better to use the nominal parameters in the case of cavitationflow, and it is better to use the effective parameters in the case of hydraulic flip flow.

Spray jet penetration and distribution of modulated liquid jets in subsonic cross-flows

Modulated liquid jets injected into subsonic cross-flows are empirically studied by using a mechanical liquid jet modulation apparatus. Experimental investigations were conducted using water over a range of cross-flow velocities from 5 m/s to 143 m/s and with modulated liquid jet frequencies from 35.7 Hz to 166.2 Hz and so on. PDPA(phase Doppler particle anemometry) was employed to measure droplet diameter and velocity with various spray cross-sections from Z/d=20 to Z/d=60. The spray structure, penetration depth, SMD(Sauter mean diameter), volume flux and velocity characteristics of modulated liquid jets injected into cross-flows were examined. As oscillation of the periodic pressure that could make liquid jet moved up and down in cross-flow field, the mixing process was facilitated. This phenomenon has the advantage of mixing the spray concentration from the center area to the outer area. Also, a bulk liquid jet puff was detected in the upper field of the liquid jet surface. The modulation effect appears significant in the extent of the spray oscillation. The correlation equations for the liquid jet boundary of the upper and lower regions which related to the Strouhal number have been presented to predict the spray structure under modulation conditions. Because of the modulation frequency, an inclination of averaged SMD for the structured layer was evanescent which contributed to the promotion of the macroscopic spray mixing process. Cross-sectional characteristics of SMD had the same tendency over a range of various modulation frequencies. As the modulation frequency increased, the region of volume flux distribution also increased.

Spray Structure in Near-Injector Region of Aerated Jet in Subsonic Crossflow

An experimental study of the breakup of an aerated liquid jet in subsonic crossflow was carried out. Digital double-pulsed holographic microscopy was used, employing a double exposure charge-coupled device sensor. The measurements include droplet locations, sizes and sphericity, and three-dimensional velocities. Droplet velocities in three dimensions were measured by tracking their displacements in the streamwise and cross-stream direction and by tracking the change in the plane of focus in the spanwise direction. The study demonstrated that digital holographic microscopy was suitable for probing the nonspherical droplets in the near-injector region. The droplet size distributions followed Simmons's universal root-normal distribution and thus could be fully described by the Sauter mean diameter alone. The distributions of the streamwise and cross-stream velocities were uniform in the near-injector region and could be characterized by the mass-average velocity except for very small and very large droplets.

Improved Model for the Penetration of Liquid Jets in Subsonic Crossflows

A theoretical model for the penetration of a liquid jet in subsonic gaseous crossflow is developed. The model allows for the deformation of the jet cross section from circular to elliptic shapes along its path. A force balance analysis on an elliptical liquid element is performed. Aerodynamic, viscous, and surface tension forces are considered counting for the nonlinear terms at large deformations. The effect of mass shedding is also included in the model. This effect changes the jet trajectory and deformation at higher Weber numbers. In addition, the drag coefficients of elliptical cylindrical elements with different aspect ratios are calculated numerically for a range of Reynolds numbers. It is observed that the drag coefficient of the cylindrical element changes considerably with Reynolds number and the jet deformation. The change in the drag force considerably affects the jet deflection in the gas stream. Results show that the liquid-to-gas momentum ratio is not the only governing parameter in predicting the jet trajectory. Gas Weber number, rate of mass shedding from the jet, jet cross-sectional deformation, variation in the drag coefficient, and variation in the liquid and gas properties all affect the jet penetration.

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.