Liquid Jets In Gaseous Crossflow Research Articles

Effects of gas viscosity and liquid-to-gas density ratio on liquid jet atomization in crossflow

Atomization of liquid jets in gaseous crossflows has many natural and industrial applications, for example, in fuel atomization in gas turbine engines, rocket engines, film cooling, and, recently, suspension and solution precursor plasma spraying processes for the development of advanced coatings. Viscosity and density of the gaseous medium may significantly vary in applications such as plasma spraying, which can affect the instability waves on the liquid jet column, resulting in a major change in the mechanism of primary and secondary breakups. In this study, a numerical model is used to investigate the impact of gas viscosity on breakup mechanisms for a wide range of density ratios and Weber numbers. Due to many challenges, only a few comprehensive atomization measurements have been performed on this subject. However, novel computational models could provide the atomization process with a thorough picture in the last two decades. The incompressible variable-density Navier–Stokes equations are solved by using finite volume schemes, and a geometric volume-of-fluid technique is used to track the gas–liquid interface. In our parametric study, three sets of density ratios and Weber numbers are chosen. In each set, four cases with different orders of magnitude of gaseous Reynolds number are simulated. Different characteristics of jet atomization are analyzed, such as the jet trajectory, breakup location, and surface instabilities generated along the jet column. Ultimately, the effects of gaseous Reynolds number, density ratio, and Weber number on jet deformation and breakup mechanisms are discussed.

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

Effects of Nanoparticle Additives on Spray Characteristics of Liquid Jets in Gaseous Crossflow

Nanofluids are attracting attention as future energy carriers owing to their high performance for improving combustion and heat transfer. In this study, the macroscopic characteristics of nanofluid jets in a subsonic gaseous crossflow were investigated by focusing on the influence of nanoparticle additives on the breakup process. Based on a distribution map of the image grayscale standard deviation, we propose an improved method to process transverse injection shadowgraphs. A simplified model of the transition mechanism from column breakup to surface breakup at a small Weber number was established. The effects of nanoparticles on the jet trajectory and column fracture position were analyzed according to the deviations from the pure liquid. To interpret the effects of the nanoparticles, a new nondimensional parameter was introduced into the empirical correlation of the column fracture position. The results indicated that at low concentrations of nanoparticles, the surface tension of the nanofluids increased slightly, while the viscosity increased significantly (by up to 23%). These changes in the physical properties had little effect on the breakup regimes or jet trajectory. Moreover, the nanoparticles promoted cavitation inside the liquid column, resulting in an additional primary breakup mode for the nanofluids. Consequently, the length of the column fracture was reduced by up to 20% compared with that of the basic fluid.

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.

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.

Theoretical Analysis of Surface Waves on Liquid Jets in Crossflows with Deformation

Liquid jets in cross air flows are widely used and play an important role in propulsion systems, such as ramjet combustors. Surface waves on the liquid jets in gaseous crossflows have been observed in numerous experiments. Especially for lower gas Webber number, liquid jets breaks up due to the surface waves. However compared with injecting into gas coaxial flow, liquid jet will be deformed in crossflow due to the transverse aerodynamic force. Deformation of jet is investigated by analyzing stress force equilibrium of the cross-section. Though linear instability analysis, dispersion relation and growth rate of surface waves of liquid jet with deformation were derived. According to the present theoretical analysis, the cross-section shape can be deformed to stable ellipse only if the gas velocity was lower than 9m/s for 1mm diameter jet. The maximum growth rate of disturbances takes place at wave number 0.7 approximately, and it will decrease with increasing the jet diameter. The range of instable wave number will expand and the most instable wave number will grow for the deformed jets.

Nozzle-Geometry Effects on Upwind-Surface Properties of Turbulent Liquid Jets in Gaseous Crossflow

An experimental study to investigate the effect of nozzle length-to-diameter ratio and the inlet curvature on the surface properties of turbulent liquid jets in gaseous crossflow was carried out. Straight nozzles with length/diameter ratios of 10, 20, and 40 were used to generate turbulent liquid jets in gaseous crossflow. The radius of curvature ofthe nozzles used was 0.6,1.2, and 2.4. The present study was limited to small Ohnesorge number liquid jets (Oh 110). The diagnostics consisted of double-pulsed holographic microscopy and shadowgraphy. The measurements included liquid-jet surface properties, breakup location of the liquid column as a whole, and the breakup-regime transitions. The measurements were interpreted and correlated using phenomenological analyses. It was observed that the injector passage length plays a role in determining the breakup length and influences the characteristics of the jet upwind surface.

Model for Deformation of Drops and Liquid Jets in Gaseous Crossflows

An analytical-numerical model is developed to calculate the deformation and spreading of axisymmetric and two-dimensional liquid drops in a gas stream for small Ohnesorge numbers and large Reynolds numbers. The model is based on an approximate series solution of the Navier-Stokes equations written for the interior flow of the drop and assuming a quasi-static gas flow. The pressure distribution on the drop surface is provided using a perturbation analysis about a trivial zeroth-order solution. The axisymmetric formulation is used for calculating the deformation of the spherical droplets, and the two-dimensional formulation is used to develop a model for predicting the spreading of the cross section of liquid jets in crossflows. The penetration of the liquid jet in the gas flow is calculated, and the results are compared with experimental and empirical results.

Bag breakup of nonturbulent liquid jets in crossflow

An experimental investigation of the bag breakup of round nonturbulent liquid jets in gaseous crossflow at room temperature and pressure is described. Pulsed photography, pulsed shadowgraphy, and high-speed imaging were used to observe the column and surface waves along the liquid jet and the formation and breakup of bags. Measurements included: wavelengths of column and surface waves, jet velocities, the number of bags along the liquid jet, the number of nodes per bag, droplets sizes and velocities, and trajectories of droplets. Present results show that the column waves of a nonturbulent liquid jet in crossflow within bag breakup regime can be explained based on Rayleigh–Taylor instability. The number of nodes per bag affected the breakup mechanism of the bags. Three distinctive sizes of droplets were produced due the breakup of the bag membrane, the ring strings and the ring nodes. The size of the droplets resulting from the breakup of the bag membrane was constant independent of the crossflow Weber number. Finally different trajectories were observed for the three groups of droplets.

Breakup of Round Nonturbulent Liquid Jets in Gaseous Crossflow

An experimental investigation of the primary breakup of nonturbulent round liquid jets in gas crossflow is described. Pulsed shadowgraph and holograph observations of jet primary breakup regimes, conditions for the onset of breakup, properties of waves observed along the liquid surface, drop sue and velocity properties resulting from breakup and conditions required for the breakup of the liquid column as a whole, were obtained for air crossflows at normal temperature and pressure. When combined with the earlier studies of Mazallon et al. (1999), the test range included crossflow Weber numbers of 02000, liquidgas momentum ratios of 100-8000, liquidgas density ratios of 683-1021, and Ohnesorge numbers of 0.003-0.12. The results suggest qualitative similarities between the primary breakup of nonturbulent round liquid jets in crossflows and the secondary breakup of drops subjected to shock wave disturbances (e.g., bag, multimode and shear breakup regimes are observed in both instances) with relatively little effect of the liquidgas momentum ratio on breakup properties over the present test range. Effects of liquid viscosity were also small for present observations where Ohnesorge numbers were less than 0.4. Phenomenological analyses were successful for helping to interpret and correlate the properties of primary breakup of round liquid jets in gas crossflows that were measured during the present investigation.