Taylor Analogy Breakup Research Articles

Computational insights into gas atomization of FeCoNiCrMoBSi high-entropy alloy: From droplet formation to rapid solidification

The intricate processes governing the gas atomization of molten metal droplets and their subsequent solidification hold paramount significance in materials science. Computational fluid dynamics simulations have emerged as indispensable tools for unraveling the complexities inherent in metal melt atomization. This study employed the volume of fluid method and the shear-stress transport k-ω turbulence model to simulate the primary atomization process of a FeCoNiCrMoBSi high-entropy alloy. Subsequently, the discrete phase model and Taylor analogy breakup model, based on the gas Weber number and incorporating primary atomization outcomes as initial conditions, were utilized to simulate droplet formation during the secondary atomization process. Analysis of the particle size distribution at the outlet of the geometric model demonstrated excellent agreement with experimental data for gas-atomized FeCoNiCrMoBSi high-entropy alloy powder. Furthermore, comprehensive characterization analyses were conducted to probe the phase constitution and structure of FeCoNiCrMoBSi powder produced by gas atomization. The results revealed that, irrespective of particle size, the powder exhibited a face-centered cubic structure and distinctive eutectic microstructural characteristics. The numerical simulation provided insights into the solidification process of secondary droplets by integrating inverse pole figure data for gas-atomized powder across varying particle sizes. The estimated cooling rate of secondary droplets ranged from 1.22 × 104 K/s to 2.64 × 105 K/s. These findings significantly advance the understanding of the gas atomization mechanism of the FeCoNiCrMoBSi high-entropy alloy, paving the way for the development of more efficient manufacturing processes for advanced materials.

A MAXIMUM ENTROPY PRINCIPLE MODEL FOR THE INITIALIZATION OF EULERIAN–LAGRANGIAN SPRAY SIMULATIONS

NOx emission regulations have become more and more restrictive for internal combustion engine-powered vehicles, especially for road transport applications. To minimize emissions and comply with regulations, selective catalytic reduction (SCR) systems are the most efficient deNOx technology thanks to the injection of a urea-water solution (UWS). State-of-the-art computational fluid dynamics (CFD) techniques employ Eulerian-Lagrangian frameworks to deal with the two phases of such problems. Still, the associated low velocities of UWS applications make it difficult to use standard breakup models (Kelvin-Helmholtz, Rayleigh-Taylor, Taylor analogy breakup) to generate initial drop size distributions. Hence, these specific studies end up needing experimentally characterized drop size distributions to initialize the CFD simulations or using expensive Eulerian-Eulerian simulations to obtain the outcomes of the primary breakup of the liquid jet. The maximum entropy principle (MEP) allows generating a droplet size-velocity probability distribution function (PDF) from initial injection conditions and injector characteristics while satisfying conservation equations. The most probable PDF curve is determined by the distribution that maximizes the entropy of the problem. A critical Weber number has been proposed to select which droplets will break up subsequently after the initial droplet break up. The model has been validated against experimental results obtained by high-resolution laser backlight imaging. Comparable results have been found and realistic tendencies were achieved, decreasing the expected droplet size with increasing injection pressures. The proposed model could help with introducing alternative breakup models for low-velocity applications without the need for prior droplet size knowledge.

Boundary element method for modeling droplet deformation in secondary atomization

A droplet deformation model based on the combination of an axisymmetric Boundary Element Method (BEM), Viscous Potential Flow (VPF) theory, and a simplified heuristic model for the action of aerodynamic forces is presented. The model predicts droplet distortion and interface shape up to the point of initial droplet break-up. To address liquid viscosity a previously introduced Generalized Viscous Pressure Correction was employed after its extension to 3D axisymmetric cases. Assumed are thin boundary layers within the droplet phase, a high density ratio between the two phases and moderate Reynolds numbers. The model requires at most around 200 flow variables to properly predict droplet deformation and distortion. The overall model produces results comparable to those of the Taylor Analogy Breakup model and its nonlinear version in the vibrational regime. However, it requires a calibration factor of 1.36 for the aerodynamic local pressure, in order to obtain the correct critical Weber number of around 12. In the bag and bag-stamen regimes, the droplet shape and distortion parameters are in good agreement with experimental data. Overall, the results indicate that the present modeling approach might be used as sub-grid model for droplet dynamics in multiphase flow simulation with a highly dispersed liquid phase.

Mechanism of rapidly solidified satellites formation in gas atomized powders: Simulation and characterization

It has been generally recognized that satellites deteriorate significantly the uniformity and stability of powder spreading in additive manufacturing (AM). Therefore, it is crucial to investigate the mechanism of satellites formation and the microstructure of collision region. In this study, the turbulent flow of gas was numerically simulated in an atomizing chamber using the shear stress transport k-ω (SST k-ω) model. Then, the Taylor analogy breakup (TAB) model and the discrete phase model (DPM) were used to analyze the breakup process of the secondary atomization of superalloy droplets which formed during the primary atomization. Meanwhile, the impact mechanism of the recirculation zone on the satellites was investigated in the atomization chamber. Scanning electron microscopy (SEM) was used to characterize the morphology and cross-sectional microstructure in the collision region of the satellites. Three collision types of satellites were identified. The findings of this study enhance the understanding of the mechanism of satellites formation and provide technical insight into the control and elimination of satellites in argon atomization (AA).

Drop Interactions with the Conical Shock Structure Generated by a Mach 4.5 Projectile

This work presents measurements of liquid drop deformation and breakup time behind approximately conical shock waves and evaluates the predictive capabilities of low-order models and correlations developed using planar shock experiments. A conical shock was approximated by firing a bullet at Mach 4.5 past a vertical column of water drops with a mean initial diameter of . The time-resolved drop position and maximum transverse dimension were characterized using backlit stereo images taken at 500 kHz. The gas density and velocity fields experienced by the drops were estimated using a Reynolds-averaged Navier–Stokes simulation of the bullet. Classical correlations predict drop breakup times and deformation in error by a factor of 3 or more. The Taylor analogy breakup (TAB) model predicts deformed drop diameters that agree within the confidence bounds of the ensemble-averaged experimental values using a dimensionless constant compared to the accepted value . Results demonstrate existing correlations are inadequate for predicting the drop response to the three-dimensional relaxation of the flowfield downstream of a conical-like shock and suggest the TAB model results represent a path toward improved predictions.

Euler–Lagrange stochastic modeling of droplet breakup and impact in supersonic flight

Blunt bodied aircraft traveling supersonically in weather environments may be damaged by impacts with water droplets and other airborne particles, such as snow and ice. Prior to an impact, these particles will encounter a bow shock that causes a discontinuity in their relative velocity with the gas phase, which can lead droplets to breakup into smaller droplets. These smaller droplets are more easily diverted from colliding with the blunt body due to their significantly reduced inertia relative to the initial rain droplets. One-way coupled Euler–Lagrange simulations are used to study the dynamics of droplets approaching a blunt body in steady two dimensional and axi-symmetric flow fields using a stochastic version of the Taylor analogy breakup model for the breakup dynamics. Ultimately, the dominant mechanism determining engineering quantities of interest was observed to be a competition between breakup time and the time available for a droplet to reach the body after encountering the bow shock. At Mach numbers 2, 3, and 6, the competition between these mechanisms was the dominant factor determining the momentum transfer to the blunt body via droplet collisions, which can be well characterized by a scaling relation.

A U-shaped spray device on a front boom-type roadheader for dust suppression in a metro tunnel

The application of the cantilever tunneling method in urban metro tunnel constructions has been gradually promoted. High concentration of dust will be produced near the working face when a boom-type roadheader is used to excavate a small and narrow metro tunnel in hard rock. If not controlled in time, high concentration of dust will escape in the working wells, the air in cities will be polluted and the health of residents will be affected. To maintain the sustainable development of cities, a U-shaped dust suppression device with optimized nozzle arrangement installed at the front end of the boom-type roadheader is proposed in this study. Firstly, the atomization characteristics of four different types of nozzles were analyzed by an indoor model test. The optimum nozzle is determined to be a fine solid conical nozzle with a diameter of 1.6 mm. Then, the dust diffusion law in the core dust producing area under the action of an air compressor is analyzed based on the discrete phase model of computational fluid dynamics; the influence of the parameters of the complete spray device on the performance parameters of the droplet field is discussed in detail based on the Taylor analogy breakup simulation method. The results show that when the spray pressure is 8 MPa and the number of nozzles is 11, the formed droplet field has the best encapsulation and the high concentration droplets account for 77.36%. Finally, the device is applied and verified on site. The test results show that the maximum total dust suppression efficiency in the tunnel reaches 81.48%, the maximum respirable dust suppression efficiency reaches 81.51%, and the dust suppression efficiency at other monitoring points is also above 70.41%.

Numerical and Experimental Spray Analysis of Castor and Jatropha Biodiesel under Non-Evaporating Conditions

Fuel spray characteristics influence combustion, which in turn has a direct impact on engine performance and emissions. Recently, there has been an increasing interest in novel castor oil biodiesel. However, few investigations have been performed that combine both numerical and experimental biodiesel spray analyses. Hence, in this paper, we aim to explore the spray behavior of castor and jatropha biodiesel by employing numerical and experimental methods under non-evaporating, varying injection, and ambient conditions. The experimental study was carried out in a control volume vessel (CVV) at high injection and ambient pressures. The fuel atomization was modelled in ANSYS Fluent using a Lagrangian/Eulerian multiphase formulation. The results revealed that the Kelvin–Helmholtz and Rayleigh–Taylor (KHRT) model coupled with the Taylor Analogy Breakup (TAB) model provide a better estimation of the penetration length (PL) and spray cone angle (SCA) compared to the KH and TAB models. On average, Jatropha biodiesel (JB-20) and castor biodiesel (CB-20) showed a 10% to 22% longer PL, 8% to 10.6% narrower spray cone angles, and 3% to 6% less spray area, respectively, compared to diesel. The numerical predictions showed that JB-20 and CB-20 had an around 24.7–48.3% larger Sauter mean diameter (SMD) and a 38.6–73.3% average mean diameter (AMD).

Study on Spray Characteristics and Breakup Mechanism of an SCR Injector

Selective catalytic reduction (SCR) is currently one of the most efficient denitration technologies to reduce nitrogen oxide (NOx) emissions of diesel engines. AdBlue (urea water solution, UWS) is the carrier of the reducing agent of SCR, and the spray process of UWS is one of the critical factors affecting denitration efficiency. In this paper, a non-air-assisted pressure-driven full process spray (NPFPS) model is proposed to illustrate the breakup mechanism and the spray distribution properties of UWS through computational fluid dynamics (CFD). In the NPFPS model, the mechanism of the primary breakup is described by the volume of fluid (VOF) approach, which realizes the quantitative study of the critical parameters determining spray characteristics such as the breakup length, inclination angle, droplet size of the primary breakup, and primary velocity. The distribution of the spray after the primary breakup is depicted by the discrete phase model (DPM) coupled with the Taylor analogy breakup (TAB) model, through which the degree of secondary breakup can be obtained including quantitative studies of the droplet size distribution and velocity distribution in the different cross-sections. To verify the accuracy and feasibility of the NPFPS model, the experimental data are employed to compare with the simulation data. The results are in good agreement, which indicate the practical value of the model.

Numerical investigation on the role of a mixer on spray impingement and mixing in channel cross-stream airflow

The present study numerically investigates the influence of introducing a spin-type mixer and different angular orientations of the mixer blades on the spray-wall interaction and mixing, following cross-stream injection of a pulsed spray into airflow in a circular duct. This is relevant to the Selective Catalytic Reduction system in diesel engines for exhaust gas after-treatment. The spin-type static mixer is located downstream of the injector and generates a swirling airflow in the duct. All simulations were carried out using ANSYS Fluent V18.0. The standard k–ω model is used to simulate the turbulent continuous phase flow, while the discrete phase model is employed to track the spray droplets. The Taylor Analogy Breakup and Kuhnke wall film models are adopted to model droplet breakup and wall-film formation, respectively. First, the swirling airflow characteristics without spray injection are validated against in-house particle image velocimetry measurements. Second, the spray computations are compared with the experiment. Overall, good agreement between simulation and experiment is achieved. Furthermore, the choice of water and urea water solution injection liquid on the in-channel spray characteristics is also studied. The main focus of the present work is on the study of the influence of spin mixer clocking on the post-impingement spray evolution, droplet redistribution and mixing, and wall-film characteristics. The results show that the choice of the angular orientation of the mixer governs the extent of droplet deposition and splashing on the mixer blades and, as a result, strongly influences the spatial uniformity of droplets and ammonia species at the channel exit.

Numerical and experimental analysis on spray characteristics of biodiesel (waste cooking oil) using pressure swirl atomizer

Atomization characteristics and evaporation have major role in air-fuel mixing and the combustion process in diesel engine. The aim of this study is to perform numerical and experimental analysis to investigate the spray pattern of biodiesel (waste cooking oil) generated from pressure swirl atomizer. The computation exhibits Eularian-Lagrangian method to comprise flow of multiphase and also linearized instability sheet atomization (LISA) model to envisage atomization, sheet breakup, and film formation. The model's strength is the identification structure of spray created from pressure swirl atomizer. A three-dimensional computational fluid dynamics work consisting of LISA and Taylor analogy breakup model are certified via experimentation taken from constant volume chamber. Further, spray tip penetration, cone angle, and sauter mean diameter (SMD) are identified for fuel (B100, B25, and D) under injection pressure of 110 and 160 MPa, and 2.8 MPa ambient pressure using swirl atomizer in constant volume chamber. This particular spray is quite important for application in diesel engines but is not extensively explored. The results reveal that as injection pressure increases from 110 MPa to 160 MPa. The spray tip penetration for B100, B25, and D are increased by 19.86%, 14.90%, and 14.50% respectively, further, cone angle at the start of injection decreases by 6%, 5%, and 3.41%, similarly, the average SMD decreases by 25%, 33.33%, and 25.4%, respectively. This is due to the rheological property of fuel, turbulent energy of droplet and air is maximum in primary breakup zone.

Theoretical deformation modeling and drop size prediction in the multimode breakup regime

A theoretical model has been proposed to incorporate internal flow mechanics to better predict the deformation and the resulting breakup of a liquid drop in a continuous uniform air jet in the multimode breakup regime. A Weber-number-dependent breakup criterion predicts the deformation of the drop at the time of the breakup, which occurs at the time the internal pressure at the drop equator exceeds internal pressure at the pole. This breakup criterion is used to determine an improved coefficient used in the Taylor Analogy Breakup (TAB) model. The TAB model is also extended to include the effects of turbulence within the drop. Hill vortices form within the drop as a result of viscous forces and flow around the drop. It is proposed that these vortices contribute to the deformation that eventually leads to the outer ring and smaller drop within the ring that is classic to multimode breakup. Instability analysis is used to model the breakup of the outer ring and predict the resultant droplet sizes. The model-predicted breakup times and ring breakup droplet diameter are compared with experimental results collected using digital in-line holography.

Effect of Rain on the Aerodynamic Performance of a Horizontal Axis Wind Turbine – A Computational Study

This paper analyzes numerically the impact of rainfall on the aerodynamic performance of a three-bladed Horizontal Axis Wind Turbine, with blades constructed by NACA 4418 airfoil. The simulations were conducted by the help of the commercial Computational Fluid Dynamics code, ANSYS Fluent. Firstly, the optimum geometry of the blade was designed with an application based on Blade Element Momentum theory. The Moving Reference Frame Model was applicated to simulate the rotation of the blades and the k-ω shear-stress transport turbulence model was added as well. The simulation of rain was accomplished by the Discrete Phase Model and the Taylor Analogy Breakup model was enabled to simulate droplets breakup. Three different rainfall conditions were studied, corresponding to Liquid Water Contents of 10g/m³, 30g/m³ and 60g/m³. The influence of droplet diameter on the aerodynamic performance of the blade was also examined. The results showed that the aerodynamic performance of the wind turbine is degraded in rain conditions, and the degradation is greater for higher values of Liquid Water Content and for larger diameter of water droplets.

Numerical Study on Flow Structures of a Hollow Cone Spray in Crossflow

In this paper, numerical investigation on the flow field structure of a hollow cone spray injected transversely into a confined crossflow is presented. The unsteady turbulent flow is predicted by adopting the Scale-Adaptive Simulation approach and the atomization of the spray is predicted by using the linear instability analysis and Taylor analogy breakup theory. The interactions between the hollow cone sprays (with two different spray angles of 80° and 40°) and the crossflow inside a rectangular duct (95 mm × 95 mm in cross-section) at ambient temperature and pressure are simulated. The results show that there exist six large-scale vortex structures in the mixing flow field, namely the Counter-rotating Vortex Pair (CVP), the horseshoe vortex, the shear layer vortex, the hairpin vortex, the wake vortex, and the upright vortex. The formation mechanisms of these vortices are analyzed. The CVP and the hairpin vortex dominate the flow field and exert significant influences on droplet dispersion in span-wise and stream-wise directions respectively. The influence of the spray angle on the vorticity of the CVP is small, but a smaller spray angle can lead to larger depths of the spray and the CVP and a smaller distance between both CVP cores.

Deagglomeration of cohesive particles by turbulence

Abstract

Atomization and spray characteristics around an ERBS using various operational models and conditions: numerical investigation

The impetus of the current paper is to conduct numerical evaluations about the fundamental behaviors of the flow in an electrostatic rotary bell sprayer (ERBS) during the formation of the droplets and depositing on a target. The effect of operational parameters like bell rotational speed, shaping air and paint flow rate, electrical charge values and droplet distributions are considered precisely. Here, an Eulerian-Lagrangian algorithm that contains a model for airflow field, spray dynamics, electric charge field, droplet trajectory tracking and wall film dynamics has been extended by using the OpenFOAM package. The fluid dynamics is computed by using a large eddy simulation (LES) turbulence model. The mechanism of atomization is facilitated by the action of the centrifugal force that conducted the disintegrated droplets to the cup edge. Following that, the high-velocity droplets affected by the shaping airflow and electric force are transported towards the workpiece. The effect of the bell rotational speed in comparison with other parameters is dominant. The measured size of the droplets is controlled by increasing the bell rotational speed or decreasing the paint flow rate, in this case, promoting a reduction in droplet size. The droplet size near the bell cup was increased noticeably, however, their radius becomes more uniform at a longer lateral distance. Investigation of the various breakup models is one of the main goals of this work to predict the droplet size more precisely. The Reitz-KHRT, Reitz-Diwakar, Pilch-Erdman and the newly modified TAB model are examined in order to predict the breakup process in the ERBS. As the paint droplets are a viscous fluid a modification of the Taylor Analogy Breakup (TAB) approach taking non-linear influences for large viscosity into account is recommended. The use of the breakup models creates a smaller droplet size and this means they are more sensitive to recirculation regions flow pattern. The implemented wall film function was able to predict the transport in the boundary layer over the target. The numerical results describe exact values for the size, distribution, velocity and trajectory of the particles in ERBS, and these results are important for coating industries, in order to optimize their working conditions.

Effects of the physical properties of fuel on spray characteristics from a gas turbine nozzle

Abstract In a gas turbine combustion system, droplet distribution in the combustor directly affects the combustion process. Fuel droplet size and droplet velocity determine the fuel droplet distribution in the combustor. The present study aims to investigate effects of physical properties on spray characteristics using computational fluid dynamics (CFD) analysis. Spray modeling was performed to analyze the spray characteristics for different fuel physical properties. The hollow cone spray of a gas turbine nozzle was modeled using a LISA (Linearized Instability Sheet Atomization)-TAB(Taylor Analogy Breakup) model with commercial CFD code called, ANSYS Fluent 16.2. The model was validated against the experimental results, which were obtained by PDPA (Phase Doppler Particle Analyzer) and spray tomography. Based on this spray model, the effect of fuel physical properties on spray characteristics were determined. In addition, because the spray patterns differed various injection fluids, the spray characteristics of the gas turbine nozzle with various injection fluids were considered from the perspective of fuel physical properties. It was found that higher density, viscosity and surface tension delayed the atomization process and that density and surface tension have a more significant effect on spray atomization, than viscosity in the catastrophic breakup regime.

Design of a Double-Nozzle Air Spray Gun and Numerical Research in the Interference Spray Flow Field

Spray painting robots equipped with air spray guns have been widely used in the painting industry. In view of the low efficiency of single-nozzle air spray guns when spraying large targets, a new double-nozzle air spray gun structure was designed in this paper based on the Coanda effect of double jets. Firstly, a 3-D physical model of the double-nozzle air spray gun was built in Solidworks, in which unstructured grids were generated for the computational domain by ICEM. Secondly, the spray painting process was numerically modeled with the help of the computational fluid dynamics (CFD) software ANSYS-Fluent 16.0. The two-phase spray flow was calculated by coupling a discrete phase model (DPM) and the Taylor analogy breakup (TAB) method. The TAB model was applied to predict the secondary break-up. The DPM model was applied to predict the droplet trajectories. The geometry of an air spray gun has a significant influence on the spray flow field characteristics. The influence of the air spray gun geometry on the interference spray flow field characteristics and coating film thickness distribution were investigated by changing the values of the distance between the centers of the two paint holes (L) and the angle between the axes of the two paint holes (θ). Numerical results show that the smaller L and θ are, the stronger the interference effect between the two jets, while the more concentrated the paint is in the central region of the target surface, the easier it is for overspray to occur. With increasing L and θ, the interference effect gradually decreased and the extension distance of the coating film along the x-axis gradually increased. However, if L and θ are too large, the interference effect will become too weak and the shape of the coating film will become a concave, with more paint on both side regions and less paint in the central region, which will cause an uneven coating film. From the simulation results, it can be concluded that a more uniform coating film can be obtained when L = 30 mm and θ = 10°. The effective coating width of the double-nozzle air spray gun was increased by 85.7% compared with the single-nozzle air spray gun, which improved the spraying efficiency.

Assessment of Droplet Breakup Models for Spray Flow Simulations

In this paper we examine droplet behavior and macroscopic atomization characteristics of a non-reactive liquid spray via a series of large-eddy simulations. In our numerical study we examine three popular models for spray atomization, namely, the Taylor analogy breakup (TAB), Reitz–Diwakar and Pilch–Erdman models, and compare their predictions against available experimental data. According to our simulations, and for the flow conditions considered herein, the TAB model exhibits a slightly better performance than the other two models do. Further, since the TAB model is known to underestimate the effect of disruptive drag forces, we present a modification to it and assess its predictive capacity. More specifically, according to the numerical test presented herein, our modification has the potential to improve the accuracy in the numerical computation of important global quantities of the spray, such as the liquid and vapor penetration distances.

Theoretical analysis on the atomization characteristics of liquid nitrogen jets

Atomization with cryogenic fluids is complicated due to the combined effects of both the mechanical breakup and thermodynamic flashing. However, the weight of the two effects on the atomization has not been determined yet. This paper proposes a hybrid mathematical model to evaluate the weight of the thermodynamic effect and aerodynamic effect. The entire process of jet spray breakup, including the primary breakup and secondary atomization, is described in the model. A linear stability analysis is carried out using the dispersion equations for the primary breakup. In the secondary atomization, the Taylor analogy breakup and bubble micro-explosion models are employed to study aerodynamic and thermodynamic effects on the atomization, respectively. The homogeneous nucleation is implemented in the bubble micro-explosion models. A criterion is obtained which can be evaluated to predict the dominant effect. Accordingly, the influence of factors such as ambient pressure and other physical parameters on the atomization process is analyzed. The results reveal that, under low ambient pressure, thermodynamic flashing is stronger. Besides, the mechanical action is restrained when the surface tension is increased.