Droplet Deposition Distribution Research Articles

植保无人机喷头角度对雾滴沉积分布的影响

During the field application of pesticides by plant protection UAV, due to the interference of meteorological factors or operating parameters, the deposition effect of droplets is poor. In order to explore the impact of the nozzle angle of plant protection UAV on droplet deposition distribution, this article is based on field experiments and collects data on different flight speeds (1, 3, 5 m/s) and nozzle angles (±60°, ±45°, ±30°, 0°), and performs variance analysis and regression analysis on the test results. The results showed that adjusting the nozzle angle had a significant effect on the amount of droplet deposition and deposition uniformity. Compared with 0°, the nozzle angle of -30° increased the amount of deposition by 76.94% and 61.04% at flight speeds of 1.2 m/s and 3 m/s, respectively. The flight speed had a significant effect on the amount of droplet deposition, and the increase in flight speed decreased the amount of droplet deposition by 55.97%-77.06% and had no significant effect on the uniformity of droplet deposition. This study provides a reference for improving the droplet deposition effect of plant protection UAV field pesticide application operations.

Spray performance of flexible shield canopy opener and rotor wind integrated boom-sprayer application in soybean: effects on droplet deposition distribution.

Canopy density is high during mid-to-late soybean growth as a result of dense planting to improve yield, which seriously affects the control of pests and diseases. The dilemmas of difficult droplet penetration, nonuniform deposition, and droplet drift in field spraying remain challenges to the precise control of droplet distribution. This paper proposed a novel spraying application mode combined flexible shield canopy opener (FSCO) with rotor wind. The design of the key components of the new boom-spraying machine are described. The effects of the comparative spraying modes on spray deposition and droplet drift were studied in a field validation test to explore the feasibility of the novel spraying application. The study found that droplet coverage inside the soybean canopy was significantly affected by spraying mode, rotor wind speed and opener depth. The spraying operation that used the FSCO and rotor wind integrated mode was optimal for droplet uniformity on the adaxial and abaxial surfaces of the canopy leaves, with droplet uniformity indices of 0.966 and 0.934, respectively. At a rotor wind speed of 6 m s-1 and opener depth of 15 cm, the soybean canopy droplet coverage uniformity effect achieved the highest composite score of 0.937. The spraying mode used in this study improved droplet coverage uniformity by 82.30% and droplet anti-drift performance improved by 99.73% compared to the conventional boom-spraying mode. The study shows validity of the spraying mode combined FSCO with rotor wind to open dense canopy and improved droplet deposition uniformity in canopy and anti-drift performance. © 2024 Society of Chemical Industry.

The effects of aerosol concentration on the evolution, transport, and deposition of hygroscopic droplets in the highly idealized MT model: A numerical study

Inhalation therapy is widely used to treat various respiratory diseases. Nebulizers have been widely adopted due to their ease of operation, high drug delivery efficiency, and low residual volume. Traditional studies on drug delivery in the respiratory tract typically use a one-way coupled method to track drug transport and deposition for non-hygroscopic drug particles. However, neglecting the concentration of nebulized hygroscopic droplet aerosols can lead to significant discrepancies in the deposition efficiency (DE) of nebulized drugs in the airways. To investigate the effect of different nebulization rates on the evolution, transport, and deposition of droplets, a highly idealized mouth-throat (MT) model was selected as a testbed for the in silico trials of drug delivery to the respiratory tract. The interaction between continuous and discrete phases was modeled using a two-way coupled model of highly concentrated droplet aerosol-water vapor interaction, innovated by the particle parcel method. The effects of different coupling methods and boundary conditions on the average droplet diameter and droplet deposition distribution pattern at the outlet of the MT model were compared using a computational fluid dynamics (CFD) method. Simulation results indicate that neglecting the effect of water vapor evaporated from the droplets on the relative humidity (RH) in the oral cavity could lead to a 2.2-fold prediction error of the average droplet diameter at the outlet of the MT model for a conventional nebulization rate of 0.386 g/min. As the nebulization rate increases, the difference in the predicted average droplet diameter at the outlet of the MT model between the one-way coupled method and the two-way coupled method also increases. Increasing the nebulization rate during inhalation therapy could lead to incomplete evaporation of drug droplets, resulting in deposition of larger diameter drug droplets in the oral cavity. In contrast, a lower nebulization rate can reduce the droplet diameter at the outlet of the MT model, allowing it to enter deeper airways.

Performance Evaluation of UAVs in Wheat Disease Control

Plant protection unmanned aircraft vehicles (UAVs) were developed rapidly in China. The operation performances of different models of UAVs were different. This paper systematically studied droplet deposition distribution; pesticide-mixture utilization rate; operational efficiency; wheat-disease control efficacy; and a comprehensive score of three types of UAVs, a boom sprayer, and a knapsack sprayer. The results showed the descending order of the droplet penetration rate of the pesticide application equipment (PAE) was boom sprayer; UAVs; and knapsack sprayer. The pesticide-mixture utilization rates of the UAVs and boom sprayer were more than 50% while that of the knapsack electric sprayer was only 27.8%. The UAVs’ average labor productivity was 5.75 ha per man-hour, which was slightly less than that of the boom sprayer and 21.3 times that of the knapsack sprayer. The control efficacy of each machine on wheat Fusarium head blight was more than 90%. The average performance comprehensive score of the UAVs was 0.812, which was slightly lower than the score of 0.929 for the 3WPZ-700 self-propelled boom sprayer but much higher than the score of 0.399 for the 3WBD-18 knapsack electric sprayer. The results clearly showed the potential of UAVs for improving the pesticide-mixture utilization rate and operational efficiency, as well as the wheat Fusarium head blight control efficacy.

Construction and testing of a model for predicting droplet deposition based on Gaussian process regression

To realize precision spraying, predicting the pesticide application dose based on the structural characteristics of the plant canopy is a crucial step. However, most of the current precision spraying techniques are based on canopy characteristics with no consideration given to the effect of canopy characteristics on droplet particle population. As a result, the droplet deposition value is far from being ideal. Herein, we explored the effects of canopy density and spraying volume on the distribution of droplet deposition in simulated citrus tree canopies and constructed a prediction model for droplet deposition. In this research, the three-dimensional (3D) reconstruction of fruit tree canopy was obtained using binocular camera and a new method was proposed to describe simulated citrus tree canopy density using three-dimensional point cloud. The optimal description of the interrelationship between 3D point cloud and fruit tree canopy density was determined by comparing the determination coefficients, Akaike information criterion and relative errors of the four fitting functions. Through our experiments, a droplet deposition prediction model based on Gaussian process regression was established by changing the duty cycle of the solenoid valve to adjust the spray volume, with simulated citrus trees as the target and water sensitive paper as the sampling method for collecting droplet deposition data. The experimental results show that the distribution of droplet deposition in the upper and lower layers of the canopy varies, but within the same layer droplets can produce relatively uniform deposition in similar canopy density areas with correlation coefficients greater than 0.6. When the canopy density reached 4.35 m2/m3, the amount of droplet deposition was anomalous. The prediction model, after training, has good ability of predicting droplet deposition with R2 higher than 0.79. At the same time, it was found in the research that differences occurred between the prediction accuracy of the droplet deposition prediction model in the upper canopy layer and that in the lower canopy layers, in which the R2 of the prediction model in the lower layer could reach 0.82, while in the upper layer it was 0.79. It is expected that our research on droplet deposition prediction can provide a new research perspective for precision spraying technology in plant protection operations.

Numerical simulation of the spatial and temporal distributions of the downwash airflow and spray field of a co-axial eight-rotor plant protection UAV in hover

The downwash airflow of a multi-rotor unmanned aerial vehicle (UAV) in hover can improve the penetration rate of droplets in the canopy of fruit trees, but the uncertain distribution of the downwash airflow can also lead to the generation of uneven distribution of droplets. With a co-axial eight-rotor plant protection UAV as the research object, the computational fluid dynamics (CFD) method is adopted in this study to establish the coupled flow field model of the downwash airflow and the two-phase flow model of airflow-droplets in hover. The spatial and temporal distribution law of the downwash airflow is analyzed, and the impact of the motion law of the droplets in the spray field is investigated. The results show that the downwash airflow shifts from an unsteady state to a steady state over time. Various wind vortices such as wake vortex, ground diffusion airflow, and vortex ring are generated during the evolution process, with a “negative velocity channel” of downwash airflow velocity identified in the central region under the rotors. The farther the airflow is from the rotor, the larger the area field of wake vortex airflow. Consequently, there is a gradual coupling of the left and right adjacent wake vortices from mutual independence, with the “spiral effect” of the downwash wind field offset by the mutual coupling of the upper and lower rotors of the UAV. When the installation position of the nozzle falls within the below-rotor region, the distribution of droplet deposition becomes more penetrative than the central axis installation position of the nozzle. It indicates that the below-rotor installation position of the nozzle can prevent droplets from entering into the coupling region of the trailing vortex, which reduces droplet drift. According to the field test, the measurement and simulation results of the downwash air velocity are consistent, with the minimum and maximum relative error reaching 4% and 29%.

Wetting and deposition characteristics of air-assisted spray droplet on large broad-leaved crop canopy.

Precision and efficient pesticide spraying is an important part of precision agriculture, banana is a large broad-leaved plant, with pests and diseases, has a high demand for spraying and pest control. The purpose of this study was to clarify the wettability of different pesticides on the banana leaf surface, and the effects of nozzle type and working parameters on the deposition distribution performance under air-assisted spray conditions. The wettability test results of different pesticides on banana leaf surfaces showed that the wettability of the adaxial side was always stronger than that of the abaxial side, the smaller the surface tension of the droplets, the better the wettability on the surface. The spray experiment was carried out on the previously developed air-assisted sprayer with the latest developed intelligent variable spray control system. Three types of nozzles were used to spray with different combinations of working parameters. The deposition distribution performance on the banana leaf surface was obtained by image processing using a self-compiled program. The experimental results show that the nozzle type, wind speed, and spray pressure have significant effects on the deposition distribution performance. Through the study of the interaction and coupling effect of nozzle type and working parameters on the spray droplet deposition distribution on both sides of banana leaves, the results show that under the conditions of hollow cone nozzle, 0.5Mpa spray pressure and 3-5m/s wind speed, the spray coverage and droplet density are in the optimal state. This is mainly due to the low spray pressure and/or wind speed is not enough to make the banana leaves vibrate and improve the performance of pesticide deposition. excessive spray pressure and/or wind speed will cause large deformation of banana leaves and make them airfoil stable, which reduces the surface deposition performance. It is of great significance for promoting sustainable and intelligent phytoprotection.

Design of a high-voltage electrostatic ultrasonic atomization nozzle and its droplet adhesion effects on aeroponically cultivated plant roots

In the process of aeroponics cultivation, the atomizer is one of the most important influencing factors on the cultivation process. This paper presented the design of an ultrasonic atomization nozzle using contact charging and a root droplet adhesion test rig. The purpose of this study was to reveal the relationship between the main operating parameters of the high-voltage electrostatic ultrasonic atomization nozzle and the atomization effect using droplet adhesion measurements. In this study, the ultrasonic effect of nozzle was achieved by using Laval tube, and the design of the key parameters for the high-voltage electrostatic ultrasonic atomization nozzle were inlet pressure, electrostatic voltage root core electrode material and spray distance; the droplet size variation and root adhesion patterns were obtained through experiments. The best operating parameters were analyzed by using the orthogonal test method, and the droplet deposition distribution of the root system at different scales was investigated in the atomization chamber. The test results revealed that when the root core electrode material was coppe and the nozzle working parameters were at 0.4 MPa of inlet pressure, at 1.75 m the spray distance, at 12 kV of the electrostatic voltage, the root system has the highest droplet adhesion. Keywords: ultrasonic nozzle, high pressure electrostatic system, droplet size measurement, root adhesion test, droplet deposition effect DOI: 10.25165/j.ijabe.20231602.7222 Citation: Gao J M, Guo Y N, Tunio M H, Chen X C, Chen Z J. Design of a high-voltage electrostatic ultrasonic atomization nozzle and its droplet adhesion effect on aeroponically cultivated plant roots. Int J Agric & Biol Eng, 2023; 16(2): 30–37.

Droplet Deposition Distribution Prediction Method for a Six-Rotor Plant Protection UAV Based on Inverse Distance Weighting.

The aim of this work is to establish a method for real-time calculating droplet deposition distribution of a six-rotor plant protection unmanned aerial vehicle (UAV). The numerical simulation of the airflow field was carried out using computational fluid dynamics (CFD). The airflow field distribution was obtained under seven flight speeds, six flight heights, and seven crosswind speeds. The relative error verified the accuracy of the numerical model within 12% between the spatial point wind speed test and the simulated value. The numerical simulation results showed that with the improvement of the UAV flight speed and the crosswind, the relative airflow produces a vortex in the downwash wind field below the UAV and reduces the stability of the downwash wind field. The discrete droplet phase was introduced in the flow field. The ground regions were divided using a small grid of 0.5 m × 0.5 m, and statistical calculations of droplet deposition rates within each grid yielded the distribution of droplets under 294 different parameter combinations. The statistical results show that the relative airflow and crosswind caused droplet convolution, and droplet drift was increased. In the actual operation of the UAV, the flight speed should be well controlled under the condition of low environmental wind to reduce the droplet drift rate and improve the utilization rate of pesticides. Based on the distribution under 294 different parameter combinations, one droplet deposition prediction method was established using inverse distance weighting (IDW). The proposed method lays a foundation for the cumulative calculation of droplet deposition distribution during continuous operation of plant protection UAV. It provides a basis for objectively evaluating the operational quality of plant protection UAVs and optimizing the setting of operation parameters.

Preliminary Evaluation of Spraying Quality of Multi-Unmanned Aerial Vehicle (UAV) Close Formation Spraying

Chemical application using unmanned aerial vehicles (UAVs) has received significant attention from researchers and the market in recent years. The concept of using drones for collaborative spraying was proposed by manufacturers for improving intelligence and work efficiency. However, chemical spraying is a professional technology in which spraying quality is the main concern. Using drones to achieve multi-unmanned aerial vehicle formation spraying and evaluating the spraying effect has not yet been reported. In this study, an indoor test platform and two UAVs for field experiments were built. Indoor and outdoor trials of close formation spraying were carried out in Guangzhou and Changji, China from the end of 2018 to 2019, respectively. The droplet density and distribution uniformity of droplets were evaluated from multiple spray overlap areas. It can be seen that simultaneous spraying was better than sequential spraying with the indoor spraying results in the outer fuselage overlap area (S1), and spraying in a short-interval mode can improve the droplet deposition distribution in the overlapping spraying area. Additionally, the droplet distribution result of sequential spraying was better than that of simultaneous spraying in the route center overlap area (S2). Also, the droplet distribution result of the long-interval mode was better than that of the short-interval mode. The uniformity of the droplets’ distribution in two spray width areas (S3) did not change significantly among the treatments.

Lower Inspiratory Breathing Depth Enhances Pulmonary Delivery Efficiency of ProAir Sprays

Effective pulmonary drug delivery using a metered-dose inhaler (MDI) requires a match between the MDI sprays, the patient’s breathing, and respiratory physiology. Different inhalers generate aerosols with distinct aerosol sizes and speeds, which require specific breathing coordination to achieve optimized delivery efficiency. Inability to perform the instructed breathing maneuver is one of the frequently reported issues during MDI applications; however, their effects on MDI dosimetry are unclear. The objective of this study is to systemically evaluate the effects of breathing depths on regional deposition in the respiratory tract using a ProAir-HFA inhaler. An integrated inhaler mouth-throat-lung geometry model was developed that extends to the ninth bifurcation (G9). Large-eddy simulation (LES) was used to compute the airflow dynamics due to concurrent inhalation and orifice flows. The discrete-phase Lagrangian model was used to track droplet motions. Experimental measurements of ProAir spray droplet sizes and speeds were used as initial and boundary conditions to develop the computational model for ProAir-pulmonary drug delivery. The time-varying spray plume from a ProAir-HFA inhaler into the open air was visualized using a high-speed imaging system and was further used to validate the computational model. The inhalation dosimetry of ProAir spray droplets in the respiratory tract was compared among five breathing depths on a regional, sub-regional, and local basis. The results show remarkable differences in airflow dynamics within the MDI mouthpiece and the droplet deposition distribution in the oral cavity. The inhalation depth had a positive relationship with the deposition in the mouth and a negative relationship with the deposition in the five lobes beyond G9 (small airways). The highest delivery efficiency to small airways was highest at 15 L/min and declined with an increasing inhalation depth. The drug loss inside the MDI was maximal at 45–60 L/min. Comparisons to previous experimental and numerical studies revealed a high dosimetry sensitivity to the inhaler type and patient breathing condition. Considering the appropriate inhalation waveform, spray actuation time, and spray properties (size and velocity) is essential to accurately predict inhalation dosimetry from MDIs. The results highlight the importance of personalized inhalation therapy to match the patient’s breathing patterns for optimal delivery efficiencies. Further complimentary in vitro or in vivo experiments are needed to validate the enhanced pulmonary delivery at 15 L/min.

Better Droplet Deposition and Internode Shortening Effects of Plant Growth Regulator EDAH on Maize Applied by Small Unmanned Aerial Vehicle Than Electric Knapsack Sprayer

Maize (Zea mays L.) lodging is an important factor limiting its yield increase worldwide. EDAH (containing 27% ethephon and 3% DA-6) is commonly used to decrease lodging. There is an urgent need to select efficient application methods of agrochemical for better spray deposition. In our research, an unmanned aerial vehicle (UAV) (15 L ha−1 and 30 L ha−1) with EDAH dosages of 72 and 90 g a.i. ha−1, and electric knapsack sprayers (EKS) (450 L ha−1) with dosages of 90 g a.i. ha−1 were used to compare the droplet deposition distribution, uniformity and maize growth. According to our research, EDAH applied by UAV had a higher droplet deposition rate than EKS; EKS had a higher droplet coverage rate, deposition density, droplet distribution uniformity. At the same dosage of EDAH, the UAV had a better effect on controlling maize growth than EKS, and almost equal effects were detected when the dosage applied by the UAVs was decreased by 20%. Considering the lodging occurrence and yield, we recommend that the dosage of EDAH applied by UAVs should be 72 g a.i. ha−1 when there is weak lodging and 90 g a.i. ha−1 when there is heavy lodging, with a spray volume of 15 L ha−1.

Comparison of Droplet Deposition, 28-Homobrassinolide Dosage Efficacy and Working Efficiency of the Unmanned Aerial Vehicle and Knapsack Manual Sprayer in the Maize Field

Brassinolides (BRs) are naturally-occurring phytohormones, which are essentially important to improve the crop adoptive capacity to various stresses. Spray volume (SV) and agrochemical application methods are associated with chemical deposition and field efficiency. The objective of this study was to compare the possible effects of 28-Homobrassinolide (HBL) dosages 18, 22, and 30 mg a.i. ha−1 for unmanned aerial vehicle (UAV) sprayers (15 L ha−1 and 30 L ha−1) and 22 mg a.i. ha−1 for Knapsack manual sprayers (KMS) (450 L ha−1) at maize silking stage on droplets deposition distribution, photosynthetic parameters, grain filling process and yield. The results showed that the droplet deposition of UAV (15, 30 L ha−1) was 47.04%, 8.89% higher than KMS. However, the UAV sprayer had a poor droplet deposition distribution. HBL significantly increased the photosynthetic parameters, grain filling rate, and yield. A UAV spray volume of 15 L ha−1 with 22 mg a.i. ha−1 significantly increased grains yield by 4.16–5.64%, 7.5–12.09% compared to KMS and CK in both years. Considering the high efficiency of the UAV sprayer and better effects of HBL on final yield, spraying 22~30 mg a.i. ha−1 with UAV spray volume 15 L ha−1 at the silking stage could be a better strategy.

Infection Dynamics of SARS-CoV-2 in Mucus Layer of the Human Nasal Cavity - Nasopharynx

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to the worldwide spread of coronavirus disease-2019 (COVID-19) since its emergence in 2019. Virus replication and infection dynamics after its deposition on the respiratory tissues require detailed studies for infection control. This study focused primarily on SARS-CoV-2 dynamics in the mucus layer of the nasal cavity and nasopharynx, based on coupled computational fluid-particle dynamics (CFPD) and host-cell dynamics (HCD) analyses. Considering the mucus milieu, we coupled the target-cell limited model with the convection-diffusion term to develop an improved HCD model. The infection dynamics in the mucus layer were predicted by a combination of the mucus flow field, droplet deposition distribution, and HCD. The effect of infection rate, β, was investigated as the main parameter of HCD. The results showed that the time series of SARS-CoV-2 concentration distribution in the mucus layer strongly depended on diffusion, convection, and virus production. β affected the viral load peak, its arrival time, and duration. Although the SARS-CoV-2 dynamics in the mucus layer obtained in this study have not been verified by appropriate clinical data, it can serve as a preliminary study on the virus transmission mode in the upper respiratory tract.

Influence of the Downwash Wind Field of Plant Protection UAV on Droplet Deposition Distribution Characteristics at Different Flight Heights

The aerial spraying of pesticides by plant protection unmanned aerial vehicles (UAV) is a process in which the spray droplet deposition on target sites occurs under the influence of the downwash wind field. The downwash wind field is the most important factor affecting droplet deposition distribution characteristics in an aerial spray. To understand the mechanism of the downwash wind field, spray tests were conducted at different flight heights by using a DJI UAV, and the downwash wind field in the three-dimensional direction (X-directional wind, Y-crosswind, and Z-vertical wind) was measured by using a wind speed measurement system for UAV. Combined with the droplet deposition of aerial spray, the distribution characteristics of the downwash wind field and the influence of the downwash wind field on droplet deposition were studied. The results showed that it had obvious differences in the distribution of the downwash wind field for UAV at different flight heights. As the flight height increases, the downwash wind field in X-direction and Z-direction showed a strong to weak trend, while the downwash wind field in Y-direction showed an opposite trend. In addition, it was found that the downwash wind field in Y-direction and Z-direction both have a significant influence on droplet deposition. With the increase of flight height, the change of the downwash wind field led to a gradual decrease in droplet deposition in the effective spray area, and droplets deposited more uniformly. For the DJI T16 plant protection UAV in this test, the optimal flight height was 2.0 m, and the downwash wind field had a better improvement effect on droplet deposition. Therefore, in order to make full use of the downwash wind field of UAV, the appropriate flight height should be selected to improve droplet deposition of liquid pesticide and achieve a better control effect for crop disease and pests when UAV is used for aerial spray operations in the field. This study revealed the influence mechanism of the downwash wind field on droplet deposition of aerial spray, and proposed appropriate operation parameters from the perspective of practical operation. It was expected to provide data support for improving the operation quality of aerial spraying and the formulation of field operation specifications.

Effects of plant protection UAV-based spraying on the vertical distribution of droplet deposition on Japonica rice plants in Northeast China

In order to study the regularity of the vertical distribution of droplet deposition on rice plants during pesticide spraying operated by a low-flying multi-rotor plant protection unmanned aviation vehicle (UAV), water sensitive spray cards were placed on the leaves at the top, in the middle, and at the bottom of rice plants to acquire data on droplet deposition. In this study, a suspension containing tricylazole and hexaconazole was used in the spraying. The water sensitive spray cards were analyzed by the droplet deposition processing software iDAS to obtain the vertical distribution of the droplets sprayed by the plant protection UAV. The results showed that 1) significant variation was found in the coverage of the droplets in different vertical positions of the rice plants. Within the effective spray width, the best coverage of the droplets was found in the area just below the rotors, whereas the coverage of areas farther away from the rotors was poor. For the different vertical positions of the rice plants, the overall droplet coverage was 58.38% at the top, 33.55% in the middle, and 11.34% at the bottom of the plants; 2) for all vertical positions, the average size of the droplets ranged between 110 μm and 140 μm, which was suitable for the control of plant diseases and insect pests. The highest droplet density was found at the top of the plants, and the distribution of the droplet density was similar in the middle and at the bottom of the rice plants; 3) the diffusion ratio at the top of the rice plants (0.84) was better than that in the middle (0.57) and at the bottom (0.37). The overall relative span could meet the requirements for the actual application. Except for the position in the middle of the plants, the relative span for the other positions of the plants was over 0.67, which is the standard value. This study demonstrated the distribution regularity of droplet deposition along with the vertical direction of rice plants during UAV-based spraying, which is of guiding significance for the use of UAVs in plant protection, the improvement of chemical utilization efficiency, and the reduction of pesticide and fertilizer pollution. Keywords: plant protection UAV, droplet deposition, Japonica rice, droplet size, vertical distribution, spraying, Northeast China DOI: 10.25165/j.ijabe.20211405.5490 Citation: Cao Y L, Yu F H, Xu T Y, Du W, Guo Z H, Zhang H Y. Effects of plant protection UAV-based spraying on the vertical distribution of droplet deposition on Japonica rice plants in Northeast China. Int J Agric & Biol Eng, 2021; 14(5): 27–34.

Distribution regularity of downwash airflow under rotors of agricultural UAV for plant protection

In the plant protection spray operation of UAVs, the process of droplet from formation to sedimentation target is affected by airflow, easy to form uneven deposition. Accurately description of rotor downwash flow field, clarification of velocity vector distribution at different heights of the UAV rotor flow field, simulation of the flow field with high precision, which are the prerequisites for accurately analyzing the droplet deposition distribution in rotor downwash flow field. Based on CFD method, the detail of rotor flow field was numerically calculated. Taking LTH-100 single-rotor agricultural UAV as the research object, the three-dimensional solid model of UAV was established, the Reynolds average N-S equation was used as the control equation and the RNG κ-e as the turbulence model to simulate the flow field of UAV in hover and lateral wind conditions, the wind velocity distribution at different altitudes of rotor downwash flow field was studied. The simulation results of the hover state showed that: In the flow field, the peak velocity appears in a circular distribution below the distal axis of the rotor. With the decrease of height, the peak velocity distribution area showed a tendency to expand gradually after small shrinkage; When the distance from the rotor was not more than 1.5 m, the downwash flow field presented an axisymmetric distribution based on the rotor axis, and the variation rate of velocity in the peak velocity was basically the same, turbulence in downwash flow field made the flow field more complex when the distance from rotor was larger than 2.0 m. On this basis, the optimal flight altitude of UAV is 1.5 m. Wind velocity test of the flow field was carried out on a rotor test bench, wind velocities at four altitudes of 0.5 m, 1.0 m, 1.5 m and 2.0 m were measured to verify the coincidence between the simulated and measured values. The test results showed that: the relative error between the measured and simulated values at four measurement heights were between 0.382-0.524, and the overall average relative errors was 0.430, which verified the confidence level of simulated values for measured values. When the lateral wind velocity was 3 m/s, 4 m/s and 5 m/s, the simulation results showed that: The distribution trend of airflow velocity at the same altitude in lateral-wind flow field with different wind speeds was similar; When the lateral wind speed was 5 m/s, the coupling field formed by the lateral wind and rotor airflow cannot reach the height of 2 m below the rotor. The results of this study can provide more accurate environmental conditions for theoretical analysis of droplet deposition regularity in the flow field, and also provide methodological guidance for the related research on rotor flow field of multi-rotor UAV. Keywords: aviation plant protection, downwash flow field, distribution regularity, numerical simulation, single-rotor UAV DOI: 10.25165/j.ijabe.20211403.4036 Citation: Liu X, Zhang W, Fu H B, Fu X M, Qi L Q. Distribution regularity of downwash airflow under rotors of agricultural UAV for plant protection. Int J Agric & Biol Eng, 2021; 14(3): 46–57.

CFD simulation and experiment on the flow field of air-assisted ultra-low-volume sprayers in facilities

In order to explore the performance of the B-ULV-616A knapsack sprayer, computational fluid dynamics (CFD) was used to simulate the B-ULV-616A knapsack air-assisted device, which features an ultra-low-volume electric sprayer. Field experiments were carried out to test the spraying effects, and the KANOMAX anemometer was used to verify the simulated results. First, the internal and external flow fields and droplet deposition distribution of the ultra-low-volume sprayer were established. The results showed that the air-assisted spray device can change the airflow speed and direction and produce a high-speed swirling airflow at the outlet of the air-assisted spray device. The high-speed airflow (maximum of 83.5 m/s) generates negative pressure (minimum of 0.099 MPa) and causes a rapid increase in the droplet velocity and a secondary droplets spray, allowing droplets to reach a longer distance. Then, the maximum relative error was 20.14%, and its average value was 9.59%, indicating that the CFD method is suitable for the flow field analysis of the air-assisted spray device. Finally, based on the greenhouse experiment, the knapsack air-assisted ultra-low-volume electric sprayer was found to effectively improve the deposition on the rear of the crop, increase the droplet density (maximum of 81/cm2; droplet density of conventional electric sprayer is 64/cm2), and reduce the deposition amount and coefficient of variation (below 20%) within and between regions. Further, it managed to reduce pesticide use (by 69.85%) and rural non-point source pollution. Keywords: CFD simulation, air-assisted sprayer, ultra-low spraying rate, deposition, air-velocity field, relative error DOI: 10.25165/j.ijabe.20211402.6013 Citation: Lu X Y, Gong Y, Liu D J, Wang G, Chen X, Zhang X, et al. CFD simulation and experiment on the flow field of air-assisted ultra-low-volume sprayers in facilities. Int J Agric & Biol Eng, 2021; 14(2): 26–34.

Effects of plant protection UAV-based spraying on the vertical distribution of droplet deposition on Japonica rice plants in Northeast China

In order to study the regularity of the vertical distribution of droplet deposition on rice plants during pesticide spraying operated by a low-flying multi-rotor plant protection unmanned aviation vehicle (UAV), water sensitive spray cards were placed on the leaves at the top, in the middle, and at the bottom of rice plants to acquire data on droplet deposition. In this study, a suspension containing tricylazole and hexaconazole was used in the spraying. The water sensitive spray cards were analyzed by the droplet deposition processing software iDAS to obtain the vertical distribution of the droplets sprayed by the plant protection UAV. The results showed that 1) significant variation was found in the coverage of the droplets in different vertical positions of the rice plants. Within the effective spray width, the best coverage of the droplets was found in the area just below the rotors, whereas the coverage of areas farther away from the rotors was poor. For the different vertical positions of the rice plants, the overall droplet coverage was 58.38% at the top, 33.55% in the middle, and 11.34% at the bottom of the plants; 2) for all vertical positions, the average size of the droplets ranged between 110 μm and 140 μm, which was suitable for the control of plant diseases and insect pests. The highest droplet density was found at the top of the plants, and the distribution of the droplet density was similar in the middle and at the bottom of the rice plants; 3) the diffusion ratio at the top of the rice plants (0.84) was better than that in the middle (0.57) and at the bottom (0.37). The overall relative span could meet the requirements for the actual application. Except for the position in the middle of the plants, the relative span for the other positions of the plants was over 0.67, which is the standard value. This study demonstrated the distribution regularity of droplet deposition along with the vertical direction of rice plants during UAV-based spraying, which is of guiding significance for the use of UAVs in plant protection, the improvement of chemical utilization efficiency, and the reduction of pesticide and fertilizer pollution. Keywords: plant protection UAV, droplet deposition, Japonica rice, droplet size, vertical distribution, spraying, Northeast China DOI: 10.25165/j.ijabe.20211405.5490 Citation: Cao Y L, Yu F H, Xu T Y, Du W, Guo Z H, Zhang H Y. Effects of plant protection UAV-based spraying on the vertical distribution of droplet deposition on Japonica rice plants in Northeast China. Int J Agric & Biol Eng, 2021; 14(5): 27–34.

CFD simulation and experiment on the flow field of air-assisted ultra-low-volume sprayers in facilities

In order to explore the performance of the B-ULV-616A knapsack sprayer, computational fluid dynamics (CFD) was used to simulate the B-ULV-616A knapsack air-assisted device, which features an ultra-low-volume electric sprayer. Field experiments were carried out to test the spraying effects, and the KANOMAX anemometer was used to verify the simulated results. First, the internal and external flow fields and droplet deposition distribution of the ultra-low-volume sprayer were established. The results showed that the air-assisted spray device can change the airflow speed and direction and produce a high-speed swirling airflow at the outlet of the air-assisted spray device. The high-speed airflow (maximum of 83.5 m/s) generates negative pressure (minimum of 0.099 MPa) and causes a rapid increase in the droplet velocity and a secondary droplets spray, allowing droplets to reach a longer distance. Then, the maximum relative error was 20.14%, and its average value was 9.59%, indicating that the CFD method is suitable for the flow field analysis of the air-assisted spray device. Finally, based on the greenhouse experiment, the knapsack air-assisted ultra-low-volume electric sprayer was found to effectively improve the deposition on the rear of the crop, increase the droplet density (maximum of 81/cm2; droplet density of conventional electric sprayer is 64/cm2), and reduce the deposition amount and coefficient of variation (below 20%) within and between regions. Further, it managed to reduce pesticide use (by 69.85%) and rural non-point source pollution. Keywords: CFD simulation, air-assisted sprayer, ultra-low spraying rate, deposition, air-velocity field, relative error DOI: 10.25165/j.ijabe.20211402.6013 Citation: Lu X Y, Gong Y, Liu D J, Wang G, Chen X, Zhang X, et al. CFD simulation and experiment on the flow field of air-assisted ultra-low-volume sprayers in facilities. Int J Agric & Biol Eng, 2021; 14(2): 26–34.