Spray Atomization Characteristics Research Articles

Near-field spray atomization characteristics at the end of injection under flash-boiling and non-flash-boiling conditions

Spray at the end of injection is a significant source of soot and particle number (PN) emissions from gasoline direct injection (GDI) engines owing to poor atomization and incomplete combustion. This study aimed to understand the spray characteristics at the end stage under various engine operating conditions. The near-field spray was recorded using a back-lit optical method coupled with a signal control device, a heating system and a fuel supply device. An innovative image processing method for quantifying spray atomization characteristics at the end of spraying was developed, and more comprehensive spray atomization data, such as the droplet area, droplet number, and Sauter mean diameter (SMD), were extracted from the image. It was found that after injection, the spray area decreased and then increased again, followed by large droplet formation, which is believed to be caused by the ball bouncing. The averaged SMD decreased 49.0 % by increasing SD from −73 °C to 42 °C. During ball bouncing (approximately 0.1 ms AEOI), all SD conditions showed more droplets, and the number of droplets under slight flash boiling conditions is the most. Ball bouncing and flash boiling jointly promote the large spray structure to break into large droplets due to limited breakup. In addition, under flash boiling conditions, as the injection pressure increases from 10 MPa to 35 MPa, the averaged SMD decreases by 35.0 % due to the promoted atomization and droplet accelerated evaporation.

Study of the effect of cavitation flow patterns in diesel injector nozzles on near-field spray atomization characteristics using a LES-VOF method

The spray atomization process plays a critical role in achieving high efficiency and reducing emissions in internal combustion engines. The fuel injection atomization process, especially the spray primary atomization process, is significantly influenced by turbulent flow and cavitation phenomena within the nozzle. In this study, based on the coupled large eddy simulation(LES) and a volume-of-fluid (VOF)method, the effects of four typical nozzle internal flow patterns on the spray primary breakup in the near-nozzle region were investigated. To realize this objective, the generation of four distinct flow patterns was accomplished through the design and construction of corresponding nozzle structures: (1) nearly single-phase flow in a tapered-orifice nozzle with low orifice location, (2) strong geometry-induced sheet cavitation flow with sheet region extending to the nozzle orifice exit in a normal cylindrical orifice, (3) vortex-induced string cavitation flow in a tapered-orifice nozzle with relative high orifice location, and (4) geometry-induced sheet cavitation is partially suppressed while it is enhanced in the orifice region close to exit in a convergent-divergent orifice. The numerical results unequivocally reveal that the initial atomization of the spray exhibits remarkable efficacy in the case of the conventional cylindrical nozzle, characterized by internal regions of substantial sheet cavitation, despite a relatively minimal flow discharge coefficient. Conversely, the normal tapered-orifice nozzle, lacking significant cavitation, demonstrates a larger flow discharge coefficient, yet its initial atomization performance is notably suboptimal.It is worth noting that the appropriate vortex-induced cavitation in the nozzle can correspond a higher flow rate with a thin string-type cavitation and simultaneously a better spray atomization quality with a strong vortex flow. Also it is concluded that a convergent-divergent nozzle with appropriate transition location can achieve strong atomization .

CHARACTERIZATION OF FULLY DEVELOPED AIR-ASSISTED SPRAY UNSTEADINESS USING RP-3 JET FUEL

The ideal spray theory of Edwards and Marx was utilized to investigate the dependence of fully developed intermittent air-assisted spray unsteadiness on operational conditions and fluid properties. Time series information of spray droplets was identified by phase Doppler particle analyzer and used for inter-particle arrival time statistics. Results demonstrated that spray unsteadiness along the spray axis and in proximity to the nozzle exit area is more pronounced than far-nozzle field and spray periphery. The unsteadiness on the spray axis exhibits a decreasing function with the fuel injection durations, whereas an increase of air injection duration significantly elongates the unstable region along the spray axis. The properties of test liquid fuels show a moderate effect on the unsteadiness of the air-assisted spray, potentially due to their inconspicuous influences on spray atomization characteristics. Chi-square method is generally the preferred method for quantifying the global spray unsteadiness when compared to the deviation of the first time gap of experimental and theoretical inter-particle time distribution. Unsteadiness results observed during high-velocity droplet spray stage are relatively distinct compared to droplet deceleration and suspension stages. This distinction can be attributed to the continuous energy input during the initial nozzle opening, emphasizing the significance of droplet velocity in determining spray unsteadiness.

A Review of the Developments of the Characteristics and Mechanisms of Airless Spraying on Complex Surfaces

The special surface appearance of complex surfaces restricts the coating film quality of spraying. The study of the atomization and film formation characteristics of typical complex surfaces, as well as the spraying mechanism, is essential for planning the spraying robotic trajectory and improving the spraying efficiency. In this paper, modeling and characteristics of the atomization and film formation process, based on CFD numerical simulations in previous studies, are systematically reviewed, focusing especially on airless spraying. In addition, the advantages and disadvantages of the existing research from the perspective of numerical models and methods are discussed. Finally, a further research direction for spraying on complex surface is prospected. Overall, a comprehensive and up-to-date review of spray atomization and film formation characteristics is considered valuable to practitioners and researchers in these fields, and will facilitate the further application of robotic spraying in the mechanical, automotive, marine, aerospace, petrochemical and other industries.

Study on the mechanism of surfactant droplet wetting and coagulation of respiratory dust: The case of AEO-9

In industrial production, spraying is the most widely used dust control method. However, the traditional pure water spray has poor dust removal effect, and the principles of droplet wetting and dust encapsulation are unclear, resulting in poor dust removal effect. In this study, based on the CLSVOF method, we investigated the dynamic wetting and coalescence process of surfactant droplets and dust particles from a microscopic perspective. By changing the size ratio between the droplets and dust particles, as well as the initial velocity of the droplets, we simulated the spreading and wetting of surfactant droplets on the dust surface and found the optimal parameter range for encapsulating respirable dust. Through the experimental determination of spray atomization characteristics, it was found that the spray pressure of 6 MPa and the use of a 1.2 mm fine atomization nozzle produced a spray field with droplet sizes ranging from 14 to 21 μm, accounting for approximately 62.4 % of the distribution. Around 60 % of the droplets had velocities between 20 and 30 m/s. Dust settling efficiency experiments were conducted under these optimal spray parameters, and the settling efficiency of respirable dust reached 84.33 % within the favorable parameter range. Numerical simulations of the dynamic wetting process of dust-fog coupling at the microscopic level, as well as macroscopic spray experiments, were carried out to validate the reliable results. This method has significant implications for the control of respirable dust.

The cavitation flow and spray characteristics of gasoline-diesel blends in the nozzle of a high-pressure common-rail injector

In compression-ignition engines, gasoline-diesel blends have been widely concerned for its potential to reach 50% thermal efficiency and ultra-low emissions. Due to physical property difference between the two fuels, the spray atomization characteristics of the blended fuels are different from that of a single fuel, and the cavitation flow characteristics of the blends in the high-pressure nozzle and their impact on the spray are not well understood. In this paper, the visualization of cavitation flow and spray characteristics of five different proportion blended fuels (D100G0, D80G20, D60G40, D40G60, D20G80) was carried out. The influence of fuel properties corresponding to the gasoline-diesel mixing ratio on the initial generation of vortex-induced cavitation, the development of transient cavitation flow process and the injection rate and spray characteristics were studied respectively. For the tapered orifice nozzle, string cavitation is captured mainly concentrating in the needle opening initial period and closing end period, which is the main factor of spray instability and fluctuations. At the injection starting, the addition of gasoline into the diesel fuel resulted in a significant increase in string cavitation strength and larger injection rate compared to the pure diesel, even if the percentage of gasoline added is small. However, the different gasoline addition ratios have little effect on the maximum intensity of string cavitation and the duration of string cavitation in the nozzle. Accordingly, the addition of gasoline increased the overall spray cone angle and spray fluctuations throughout the injection process. Meanwhile, as the injection volume increased, the injection rate curve in the initial process is flat at first and then become steep which was precisely related to the cavitation of the vortex line in the nozzle. The findings of this paper are important guidelines for the determination of fuel injection strategies and spray analysis of gasoline-diesel blends for compression-ignition engines.

Comparative Spray Atomization and Evaporation Characteristics of Dimethyl Ether and Mineral Diesel

Abstract Dimethyl ether is a new-generation alternative fuel to mitigate cold-start issues in compression ignition engines. It has a higher cetane number and can efficiently lead to superior atomization and evaporation characteristics. This computational study compares Dimethyl ether and baseline diesel sprays in a constant-volume spray chamber. This simulation study compares spray and evaporation characteristics en-hancement due to Dimethyl ether adaptation. Fuel properties greatly influence spray atomization and evaporation characteristics. This study is based on the Eu-lerian-Lagrangian approach adopted in the Reynolds-averaged Navier-Stokes framework. The liquid spray penetration obtained by simulations matched well with the experimental results of Dimethyl ether and baseline diesel. Spray model con-stants were tuned for diesel and Dimethyl ether separately, as the fuel properties of both test fuels are completely different. These tuned models were used to simulate Dimethyl ether and diesel sprays at fixed fuel injection timings and ambient condi-tions. Results showed a lower spray penetration length for Dimethyl ether than die-sel because of the flash boiling of Dimethyl ether. Smaller diameter droplets formed due to Dimethyl ether's lower viscosity, density, surface tension, and higher evapora-tion rate. The reduction in Sauter mean diameter was quite sharp after the start of injection for the Dimethyl ether. Diesel spray showed retarded atomization and evaporation compared to Dimethyl ether. The vapour penetration length of both fuels was almost the same; however, the vapor mass fraction was higher for Dime-thyl ether than baseline diesel. Dimethyl ether spray showed superior spray atomi-zation and improved evaporation of Dimethyl ether droplets.

Numerical simulation of the dynamic wetting of coal dust by spray droplets

The dust particles generated during coal mining and processing are generally removed by spray dust reduction. The dynamic process via which spray droplets wet and wrap coal dust can directly affect the spray dust reduction efficiency. Here, we analyzed the contact wetting and wrapping process of dust particles by droplets under different particle size ratios and different initial droplet velocities. The results show that the larger the particle size ratio θ of the droplets and dust particles, the greater the variation in the dimensionless spreading coefficient. When the particle size ratio is more than 2, the droplets can completely wrap the coal dust particles. If the initial velocity is too small, the droplets will shrink and return to form a single sheet after coming into contact with the coal dust. With increasing velocity, the dimensionless spreading coefficient increases rapidly, and the coal dust is moistened and rapidly wrapped. By experimenting with various spray atomization characteristics, when the spray pressure is 6 MPa，the droplet size distribution in the spray field accounting for the highest proportion is 10 μm. Under the optimized parameters, the settling efficiency of respirable dust at each measuring point of mine return air duct reaches 86.2% on average.

A Numerical Study on Spray Combustion and Emissions Characteristics of n-Heptane, Dimethyl Ether, and Their Blends in a Constant Volume Combustion Chamber

Abstract Dimethyl ether appears to be a better choice among various diesel alternatives due to its high cetane number and sootless combustion. However, the physical and chemical properties of dimethyl ether are very different from those of diesel. The physical properties influence spray formation and atomization characteristics, while chemical properties determine combustion and emission formation characteristics. Thus, fuel's physical and chemical properties significantly determine engine performance and emissions. In the present work, spray combustion and emission formation characteristics of n-heptane, dimethyl ether, and their blends (10, 25, and 50% dimethyl ether in n-heptane) were numerically studied in a constant volume chamber. Results show that the n-heptane spray combustion has the highest heat release rate with an intense premix combustion phase, whereas dimethyl ether spray combustion has the lowest heat release rate and shortest premix combustion phase. The magnitude of the premixed phase and heat release rate decreases with the increase in dimethyl ether mass fraction in the blends. Soot, carbon monoxide (CO), unburned hydrocarbon (UHC), and nitric oxide (NO) emissions decreased with the increase in the dimethyl ether mass fraction in the blends and were lowest for the dimethyl ether.

Macroscopic and Microscopic Spray Characteristics of Dimethyl Ether in a Constant Volume Spray Chamber Using a Mechanical Fuel Injection System for Automotive Applications

Abstract Spray investigations are critical for understanding internal combustion engine combustion. Optimised spray atomisation helps improve engine output/performance and reduce tailpipe emissions. The spray from the injector nozzle depends on nozzle hole diameter, fuel injection pressure, ambient density, pressure and temperature in the spray chamber, and test fuel properties. This study evaluated macroscopic and microscopic spray characteristics of dimethyl ether (DME) and baseline diesel under atmospheric conditions (1.013 bar pressure at 298 K temperature). It correlated the spray parameters with distinctive physicochemical properties of diesel and DME using dimensionless numbers, namely Reynolds number, Weber number, and Ohnesorge number. The fuel injection system consisted of a high-pressure mechanical injection pump and mechanical fuel injectors having an original equipment manufacturer fixed nozzle opening pressure in the constant volume spray chamber. The microscopic spray investigations were performed using a phase Doppler interferometer along the spray direction at three axial distances (50, 70, and 90 mm) from the nozzle. The three orthogonal spray droplet velocities of diesel and DME were compared. The droplet number-size distributions for baseline diesel and DME were compared. Macroscopic spray characteristics were evaluated using high-speed imaging. Reynolds number was higher for DME, leading to more turbulence in the spray and accelerating the spray breakup phenomenon. Weber number of DME was also much higher than baseline diesel due to its lower surface tension. The higher Weber and lower Ohnesorge numbers justified the finer droplets of DME sprays. DME showed superior spray atomization characteristics than baseline diesel, leading to superior fuel–air mixing and efficient and sootless combustion.

Simulation Study of the Swirl Spray Atomization of a Bipropellant Thruster under Low Temperature Conditions

The spray atomization of an injector significantly influences the performance and working life span of a bipropellant thruster of a spacecraft. Deep space exploration requires the thruster to be able to operate reliably at a low temperature range from −40 °C to 0 °C, so the effect of low temperature conditions on the atomization characteristics of injector spray is motivated to be comprehensively investigated. To study the swirl atomization characteristics of MMH (methylhydrazine), which is more difficult to atomize than NTO (nitrogen tetroxide), numerical simulations were conducted, employing the methods of VOF (volume of fluid) and LES (large eddy simulation) under low temperature conditions. The physical model with a nozzle size of 0.5 mm and boundary conditions with a velocity inlet of 3.89 m/s both follow the actual operation of thrusters. The development of spray atomization at low temperatures was observed through parametric comparisons, such as spray velocity, liquid total surface area, droplet particle size distribution, spray cone angle and breakup distance. When the temperature decreased from 20 °C to −40 °C at the same condition of flowrate inlet, those atomization characteristics of MMH propellant vary following these rules: the spray ejection velocity of MMH is significantly reduced by 7.7%, and gas-liquid disturbance sequentially decreases; the liquid film development is more stable, with a negative influence on atomization quality, causing difficulties for primary and secondary breakup, so the total surface area of droplets also decreases by 6.4%; the spatial distribution characteristics, spray cone angle and breakup distance vary less than 5%. Therefore, the low temperature condition can directly lower the combustion efficiency of thrusters with obvious performance degradation, but there are no significant changes in the propellant mixing and liquid film cooling. It is concluded that the bipropellant thruster can reliably work at low temperatures around −40 °C for deep space probe operation.

Computational Investigations of Spray Atomization and Evaporation Under Cold-Start Conditions of a Diesel Engine

Abstract Unburnt hydrocarbon emissions and combustion instability are severe issues in diesel engines during cold starting. This simulation study aims to provide insights for improving the cold-start issues of diesel engines. Computational analysis of the diesel spray and evolution of plumes from a 7-hole injector was done in a constant volume quiescent spray chamber for analyzing the effect of fuel temperature. This study was based on a comprehensive numerical analysis using CONVERGE computational fluid dynamics (CFD) software, where an Eulerian–Lagrangian approach was adopted in a large eddy simulation (LES) framework. Diesel engine-like cold-start conditions were replicated by reducing the fuel temperatures to 250 K to simulate freezing conditions outside. This computational study compares fuel sprays at 250 K with 312 K into a relatively colder ambient temperature of 626 K vis-a-vis high-temperature diesel engine-like ambient conditions with ambient temperature to 961 K to investigate the degree of spray characteristics improvements due to increased fuel temperature. The predicted liquid spray penetration obtained by simulations agreed well with the experimental data for fuel temperatures injected into the ambient at cold (626 K) and hot (961 K) engine-like ambient conditions. The available empirical relations justify the simulation results of this study. Results showed that fuel and ambient temperatures significantly affected the spray atomization and evaporation characteristics. A higher reduction in liquid penetration length was found with increasing fuel temperature at hot ambient conditions. Increasing ambient temperature also improved the evaporation characteristics of the spray droplets. Vapor formation for the same increase in fuel temperature was higher at hot ambient temperature than the cold. Fuel temperature had a major role in the spray atomization process, whereas the ambient temperature affected the spray evaporation process. However, fuel and ambient temperatures had only a minor effect on the distribution of total kinetic energy (TKE). Among all test conditions, a fuel temperature of 312 K sprayed in hot ambient conditions showed superior fuel spray atomization and evaporation. Hence, to tackle the cold-start of diesel engines, measures taken to increase the fuel and ambient temperatures simultaneously proved to be useful.

Spray dynamics and atomization characteristics of multi-hole GDI injectors under flash boiling conditions

• About 100 points on the 30 mm plane below the injector was measured by using PDPA. • The effect of hole angle and air entrainment on spray atomization was analyzed. • The atomization uniformity of flash boiling spray in the space was improved. In the gasoline direct injection (GDI) engine, spray atomization contributes significantly to the formation of a uniform mixture and the effective combustion of the spray. In this study, a phase Doppler particle analyzer (PDPA) was used to measure the spray atomization characteristics of two five-hole GDI injectors with different hole arrangements under subcooled and mild flash-boiling conditions (superheated degree = 20 °C). Based on the spray patterns of the two injectors on a plane 30 mm below the injector tip, the two injectors were called triangle-patterned and pentagon-patterned injectors. A total of 100 measuring points were selected on a plane 30 mm below the injector tip, and the spray droplet diameter and velocity at these points were measured to understand the overall atomization characteristics of the spray in space. The experimental results indicated that as the spray transitioned from subcooled to flash boiling conditions, a polarization phenomenon occurred in which the velocity in the center of the plume increased and the velocity in the peripheral region of the plume decreased. However, the spray droplet diameter significantly decreased under flash-boiling conditions. The average Sauter mean diameter (SMD) of the two injectors on a plane 30 mm below the injector tip decreased by approximately 4 μm, and the uniformity of the spatial distribution of the SMD also increased. Compared with the triangle-patterned injector (injector A), the average SMD of the pentagon-patterned injector (injector B) was slightly smaller; this was attributed to the stronger air entrainment inside the spray and the enhanced air flow caused by the larger plume spacing of the pentagon-patterned injector.

Electric field and spraying characteristics of electrospray using concave ground electrode

A curved surface is used as ground electrode for an electrospray system. An experimental study of ethanol electrospray is conducted to obtain the droplet size and velocity distribution, and the dispersity of droplet size distribution is calculated. The spatial electric field distribution of the ground electrode structures with different radii of curvature is obtained numerically. The results show that when the radius of curvature of the ground electrode is 50 mm, the mono-dispersity of the droplet size is the best, and the droplet size and velocity are small, also the distribution is uniform, and the spray atomization characteristics are superior.

Spray atomization characteristics of biomass pyrolysis tar: Influence of methanol addition, temperature, and atomization pressure

Pyrolysis tar, the main by-product of low-temperature biomass pyrolysis, can potentially replace fossil fuels and help achieve carbon neutrality. The efficient atomization of pyrolysis tar is a prerequisite for clean combustion. In this study, an experimental platform was built to explore the influence of methanol addition, temperature, and atomization pressure on the spray atomization of pyrolysis tar. The results indicated that methanol addition was more effective at improving the pyrolysis tar fluidity than heating at temperatures lower than 40 °C. There was no significant change in the composition of pyrolysis tar after adding methanol. The atomization results showed that the optimal experimental parameters were 12 wt% methanol, 80 °C, and an air pressure of 0.6 MPa. The addition of methanol had little effect on the spray angle, which was mainly affected by the atomization pressure. The r value was used to measure the degree of the effect of process parameters, and the degree of the effect increased with the r value. For the spray droplet size, the r values of methanol addition, temperature, and air pressure were 57.3, 9.1, and 8.8. In contrast, for the spray angle, the r values were 3.6, 2.4, and 9.8, respectively.

Droplets velocity and diameter variations of wall impinging spray created by slicer

Microscopic characteristics of the impinging spray have a significant effect on atomization and pollutant emissions. Therefore, understanding the droplet behavior of the impinging spray comprehensively is essential to evaluate the spray atomization characteristics. However, in experiments, the size and distribution of droplets are hardly investigated in direct-injection spark-ignition (DISI) engines because of the high droplet density during the fuel injection period. In this paper, a spray slicer was adopted to cut the dense spray into thin flake with the objective of observing discrete droplets. And the particle image analysis (PIA) technique was used to detect droplet behaviors at different locations under various injection pressures of 10, 20, and 30 MPa. The results showed that the number density and velocity of droplets at the spray tip gradually decreased along the direction of spray development. The droplet away from the wall has a larger Y component of velocity (Vy). Furthermore, with an increase in injection pressure, the droplet velocity at the spray tip increased dramatically, and the atomization was greatly improved. Besides, sauter mean diameter (SMD) significantly declined at the upstream. However, Weber number (We) was almost the same at the fixed downstream locations under all injection pressures. Finally, We distribution of droplets concentrated at significantly smaller values under the fixed pressure. With an increase in injection pressure, We of droplets distributed near a large value range at all fixed locations.

Influence of atomizing core on droplet dynamic behavior and machining characteristics under synergistically enhanced twin-fluid spray

The droplet dynamic behavior of spraying during the manufacturing process affects tool life, cooling, and lubrication. A detailed understanding of droplet dynamic behavior is required to improve the surface quality while reducing the cutting fluid consumption. In this study, quantitative measurements for droplet diameter, number concentration, and axial velocity were carried out through a phase Doppler particle analyzer technique. The droplet characteristic spatial distributions of a standard twin-fluid nozzle (STN) and a novel twin-fluid nozzle (NTN) under different gas-to-liquid mass ratio (GLR) values were analyzed in detail. The results showed that the high-speed internal gas flow of an atomizing core has a significant effect on improving the synergistically enhanced atomization behavior, and more smaller droplets and an increased droplet momentum are easily obtained. Furthermore, a better spatial distribution of atomization characteristics can be achieved under a higher GLR of 4.3%. Furthermore, the effects of the novel atomizing core structural parameters on the droplet mean velocity spatial distribution, droplet turbulence, and root mean square velocity fluctuation were investigated. The results also showed that the improved NTN can effectively improve the spray atomization performance and droplet dynamic characteristics. In addition, comparative studies of the effect of the atomizing core structure on the machining performance were performed. Compared with the STN, the improved NTN achieves a significant reduction in cutting temperature, tool wear, and surface roughness of 17.25%, 33.96%, and 37.83%, respectively, owing to the better droplet dynamic characteristics and spatial distribution of spray atomization characteristics.

In-nozzle flow and spray characteristics of large two-stroke marine diesel fuel injectors

To further increase efficiency as well as to reduce emissions of large two-stroke marine Diesel engines, the understanding of the fuel injection processes and the resulting spray atomization characteristics is of high importance. The sheer dimensions, the uniflow scavenging design with the central exhaust valve position and the high swirl motion of the charge air is imposing the need for peripheral multiple fuel injector arrangement. The two or three fuel injectors are arranged by 180° resp. 120° and hence, a strongly asymmetrical and eccentrical atomizer design is given as all of the typically five orifices face a similar direction which is defined by the injector position and swirl flow. Experiments have shown that these characteristic nozzle tip bore arrangements lead to a strong spray deflection due to inhomogeneous velocity profiles induced by cavitation inside the orifice. Specifically designed transparent nozzles have been utilized to qualitatively investigate the in-nozzle cavitation flow phenomena. Furthermore, the influence on the subsequent atomization behaviour by simultaneously acquiring the spray morphology has been studied. A simplified transparent one-hole nozzle was used with a matching nozzle tip geometry representative for a large two-stroke marine Diesel engine injector. Fuel pressures of 50 MPa were applied to meet engine realistic injection conditions. Moreover, different degrees of hydro-erosive grinding were applied to the orifices to investigate the effects on the spray morphology with decreasing levels of in-nozzle flow cavitation derived by increasing inlet radii between main nozzle tip bore and orifice.

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.

Droplet Size Distribution Characteristics of Aerial Nozzles by Bell206L4 Helicopter under Medium and Low Airflow Velocity Wind Tunnel Conditions and Field Verification Test

To investigate the spray atomization characteristics of aerial nozzles adapted to manned agricultural helicopters under medium-low airflow velocity (0 to 27.8 m/s) conditions, the droplet size test was carried out in both wind tunnel and field tests. In the wind tunnel test, the laser diffraction device (LDD) was used to test the spray droplet size of CP02, CP03, and CP04 aerial nozzles. A Bell206L4 helicopter was used in the field test. The results in the wind tunnel test showed that due to the nozzles had been used for a long time and the cause of wear, the spray stability of individual nozzles was affected during the test. The limitation of droplet size measurement by using LDD was also found. The field test results showed that the main distribution range of the droplet size measured in the field test was consistent with the results of the wind tunnel test, but the droplet size value was significantly higher and the uniformity of droplet size distribution was poorer than the wind tunnel test value due to the influence of the actual environment. However, the results of field test and wind tunnel test can still be used as a reference for each other.