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This study aims to develop a low-drift air induction (AI) nozzle that meets the requirements of agricultural control unmanned aerial vehicles (UAVs). An AI nozzle was designed and manufactured to satisfy the design goals. The performance of the developed AI nozzle was quantitatively evaluated in terms of injection flow rate, air-to-liquid ratio (ALR), spray angle, and droplet size. The average value of the injection flow rate and the variation over time were measured using a gear-type positive displacement precision flow meter. The spray structure and spray angle were obtained at very high temporal resolution using the single image acquisition function of a two-dimensional particle image velocimetry (PIV) system. The droplet size of the spray was measured using a laser diffraction technique. The injection flow rate of the AI nozzle changes with the pressure recovery characteristics inside the nozzle mixing chamber and affects the dynamic stability of the AI nozzle. The spray angle of the AI nozzle with a flat-fan nozzle tip increases linearly with the injection pressure, and if there is additional consideration for the two-phase flow effect, the prediction equation for the single-phase flow can be applied to estimate the spray angle. The generation of air bubble-containing droplets in AI nozzles is formed by large-diameter ligament disintegration caused by a rolled-up liquid sheet and is larger than that of single-phase flow nozzles. The droplet size (Dv0.5) of the developed AI nozzle was 384 μm, which was smaller than that of a similar commercial AI nozzle. AI nozzle design, manufacturing and performance evaluation technology that satisfies the requirements of agricultural control UAVs, was established through this study.

The downwash flow produced by agricultural drones has a great influence on the coverage ratio and the drift potential of pesticide spray droplets. Therefore, the configuration of the boom and the position of the nozzle of the pesticide injection system should be adjusted on the basis of the characteristics of the downwash flow. However, although many studies have been conducted, few studies have quantitatively investigated the characteristics of downwash flow. In this study, the average characteristics and turbulence of the downwash flow formed by a single blade were quantitatively evaluated. The single rotor blade used in the test had a radius of 370 mm, and this length was used to normalize the measurement positions. Downwash flow was measured at 400 mm × 400 mm at 10-mm intervals in the X-Y plane and for 6 measurement planes at 100-mm intervals along the Z-direction. The rotational speed of the blade was set to 2000, 2500, and 3000 rpm, and the corresponding blade tip velocities were 71.17 m/s, 88.97 m/s, and 106.76 m/s, respectively; these values were used to normalize the mean and turbulent velocity components. The velocity of downwash flow was measured using a constant temperature anemometer (CTA)-type hot-wire anemometry with an X-type probe, and data were collected at a sampling rate of 30 kHz for analysis of the turbulence characteristics. From this experimental study, the axial, radial, and tangential velocity components of the downwash flow, based on the maximum value, were 20%, 4.8%, and 5.9% of the blade tip velocity (VBtip), respectively. In addition, the turbulence intensity of the axial, radial, and tangential velocity components was 8.5%, 3.0%, and 4.5%, respectively, based on the maximum value, and the axial component was approximately twice as high as the other two velocity components. High turbulent intensity appeared near the shear flow region at high axial velocities. The downwash flow generated by a single rotor blade showed a steep velocity gradient with the blade length and axial distance, and the turbulent intensity was high in the shear layer region of the mean flow field.

Delivering pesticide droplets accurately to a target has always been a challenge for crop spraying. Pesticide spray that drifts or runs-off the crop are major sources of soil and groundwater pollution and encourage pesticide overuse. This study optimised an agricultural air-induction nozzle to overcome these difficulties. Various configurations were designed and manufactured to investigate the geometrical parameters. A range of experiments were designed and carried out to simulate field conditions and examine spray structure, stability, droplet size range, and the probability of microbubbles to determine correlations between droplet size and spray drift and droplet rebound potential with or without entrained microbubbles. The performance of the designed nozzle was compared to that of commercial nozzles. Optical diagnostic methods, including high-speed photography, laser diffraction-based droplet sizing, and microscopic flow visualisation, were employed to perform accurate investigations of droplet size range and microbubble presence potential. In addition, the spatial distribution of spray influenced by lateral wind was investigated in an open-type wind tunnel and measured using a 2-dimensional patternator and water-sensitive papers. The rebound potential of the droplets was investigated using high-speed photography for artificial leaves. The results demonstrate the significance of geometrical design factors on the performance of nozzles and the effectiveness of induced air on the reduction of drift and rebound potential. Droplets including microbubbles were found to distribute across the surface of the target leaves on impact and exhibit increased rebound resistance.

In this study, the atomization characteristics and drift potential of injection nozzles used in the pesticide injection system of agricultural drones currently used in Korea are evaluated. Furthermore, technical methods to reduce drift potential are determined. To this end, atomization characteristics were evaluated by selecting four representative nozzles commonly used in domestic agricultural drones. Additionally, an experimental device, consisting of a wind tunnel, was constructed to simulate the field situation. Moreover, drift potential was evaluated by using a water-sensitive paper under side wind conditions. The VMD and RSF of the nozzles used in the test were shown high in the order of TX–XR–TP, and the number density was low in in the order of TX–TP–XR. Thus, the evaluation of the droplet drift potential with respect to the side wind revealed that large amount of droplet drift occurs due to the side wind of 1 m/s, and the droplet drift of all nozzles used in the experiment, with the exception of the AI nozzle, was high. When the nozzle was installed obliquely, considering the flight speed and flight angle of the drone, it was confirmed that the tilt angle of the nozzle installation affects drift reduction. This applies even to nozzles that produce small droplets of less than 200 μm. Furthermore, as the speed of the side wind decreases, the drift reduction effect increases. Given that the drift potential of XR and TP nozzles, which are currently most commonly used in agricultural drones, are evaluated to be weak, auxiliary drift reduction methods, such as nozzle tilt angle, should be actively considered to reduce drift potential and minimize environmental damage.

Atomization characteristics with viscosity have motivated a number of works to investigate the flow behavior with temperature variation. An experimental study on the atomization characteristics of an aviation fuel was performed to investigate the effects of fuel temperature and its physical properties on the atomization quality and spray structure. A pressure-swirl-type atomizer as a wide-range-applicable nozzle in industrial field and gas turbine combustors was employed to inject the aviation fuel into a gaseous medium. The experiments were conducted by optical diagnostic methods, namely, phase Doppler particle analyzer (PDPA) to measure droplet size and velocity and particle image visualization to capture spray structure. Changes in physical properties of the fuel altered the spray structure, droplet distribution, and atomization quality, which apparently are effective in combustion efficiency and combustion products. Spray development was mapped with the effective parameters from the unstable to fully developed stage. It was also found that decreasing the fuel temperature degrades atomization quality, decreases spray angle and velocity component values, and generates a lower number of fine droplets. Pursuing the effects of injection pressure and temperature on the atomization characteristics led to correlations for predicting spray angle and mean SMD. The findings contribute well to the literature and clarify the atomization process with temperature variation.

Recently, agricultural drones have been widely used for precise agricultural control. In the case of drone control, improved coverage and reduced drift potential of chemical sprays are of major concern, and this is greatly influenced by the downwash flow characteristics formed by the rotor blades. In this study, the mean and turbulent flow characteristics of the downwash flow generated by a single blade of a four-sided agricultural control drone were quantitatively evaluated. The blade radius used to generate the downwash flow was 370 mm, and the measurement position was normalized using this length. In addition, the rotational speed of the blade was 3000 rpm, and the velocity components were dimensionlessly expressed using the blade tip velocity (VBtip) corresponding to this rotational speed. The velocity of downwash flow was measured using CTA-type hot-wire anemometry with an X-type probe, and data were collected at a sampling rate of 30 kHz for turbulence characteristics analysis. The mean velocity, vorticity distribution, turbulence intensity, and Reynolds stress of the fluctuation velocity were quantitatively measured. From extensive experimental works, it was revealed that a high axial velocity is formed at a specific position (r/Lb = 0.4–0.8) along the blade length. The radial velocity shows an asymmetric distribution in the plane close to the blade, and the tangential velocity is higher in the central part of the downwash flow than in the region of a high axial and negative radial velocity. An asymmetric spiral rotational flow with low axial velocity and low-pressure distribution exists inside the downwash flow due to the shear flow, and the influence of the driving motor almost disappears at the axial position (Z/Lb ∼ 1). The averaged mean value of the axial, radial, and tangential velocity components measured at six axial planes and normalized by blade tip velocity (VBtip) is composed of the ratio of the axial velocity component of 12.8%, the radial velocity component of 0.19%, and the tangential velocity component of 1.3%. The maximum values of the turbulence intensity of the axial, radial, and tangential velocity components were estimated as 6.8%, 3.0%, and 4.3%, respectively.

Air induction nozzle has been used in many applications to decrease the drift potential and increase the crop protection efficacy. The efficient operation and design of these nozzles require understanding the flow characteristics inside the nozzle. Compared to other types of nozzles the studies related to air induction nozzles are very limited especially those concerned with the internal flow. The most important parameter that characterizes the operation of AIN is the air-liquid ratio. There are no studies investigate the effect of internal flow behavior and geometric parameters on the air-liquid ratio. Therefore, the main goal of this study is to investigate the influence of geometric parameters on air-liquid ratio based on the internal flow characteristics. The volume of fluid (VOF) method was used to investigate the internal flow characteristics of an air induction nozzle (AIN). The effect of internal flow characteristics on the air-liquid ratio (ALR) that defined as the ratio between air to liquid mass flowrates was studied. The analysis results of the air-liquid ratio were validated via comparison with the experimental results. The simulations were carried out using the STAR CCM+ software. Different mesh sizes and turbulence models were tested to achieve the best results agree with experimental results. The realizable k-e turbulence model and mesh with a base size of 0.07 mm at throat diameter of 14 mm and diffuser angle of 20O had the best results so the internal flow was studied using these parameters. The results demonstrated that the performance of AIN represented by ALR was affected by the internal flow characteristics such as velocity, pressure, and film thickness. The effect of diameter ratio (the ratio of throat diameter to pre-orifice diameter) and diffuser angles on the ALR was also investigated. Increasing diameter ratio resulted in increasing ALR at a certain value and then decreased. While increasing diffuser angle resulted in a slight increase in the ALR with further reduction at a diffuser angle of 40O.

Abstact The atomization and combustion characteristics of fuels injected in aviation gas turbine engines are very important in the research and development of gas turbine combustors and have a significant impact on engine efficiency and pollutant emissions. In this study, spray atomization characteristics of pre-filming airblast nozzles developed for use in aviation gas turbine combustors were experimentally investigated for different air to liquid ratios (ALR) and air pressure differences (ΔP (%)). Pure water and Jet A-1, which have different viscosities and surface tensions that greatly affect the atomization characteristics, were used as the working fluid. Spray atomization characteristics were investigated by simultaneous measurement of droplet sizes and velocities using PDA (phase Doppler anemometry) and spray visualization using a CCD camera coupled with a Nd:YAG laser as a light source. The atomization characteristics of water and Jet A-1 showed significant differences in spray angle, velocity distribution and mean droplet size. Jet A-1 spray with lower surface tension showed a smaller mean drop size (WMSMD) than water spray did. As the ALR increased, the mean droplet size of the two liquids decreased. From the analysis of the spray flow characteristics, the surface tension associated with aerodynamic instability was the dominant variable in the atomization process with liquid sheet disintegration. The experimental constants included in the previously proposed empirical formulas for predicting the mean droplet size of the pre-filming airblast nozzle spray were presented for the two liquids used in the experiment.

With advances in the fuel spray field, much attention has been paid to the atomization characteristics of aviation fuels. The physical properties of fuels play a vital role in their resulting spray structure and spatial distribution of droplets. These characteristics are becoming more important for choosing alternative fuels for optimal performance in next-generation gas turbines. The current study experimentally investigated the atomization quality and spray structure of aviation fuels with different viscosities sprayed through a pressure swirl-type nozzle by employing laser diagnostics. A set of CCD cameras synchronized to the Nd:YAG laser characterized the spray structure, and the size and velocity of the drops were quantified by the phase Doppler technique. The fuels were tested under various temperature and injection pressure conditions. An alteration in both the injection pressure and the physical properties of the fuel were found to significantly dominate the spray structure and atomization quality. The transitional development of hollow-conical sprays was shown to require a sufficient amount of swirl intensity, characterized by their physical properties and injection pressure. Fuels with a lower viscosity were experimentally found to generate well-developed hollow-conical sprays with finer drops, wide distribution in size, and higher velocity components, which are recognized as ideal spray properties in the combustion field.