Downwash airflow field distribution characteristics and their effect on the spray field distribution of the DJI T30 six-rotor plant protection UAV

Spray characteristics are the fundamental factors that affect droplet transportation downward,deposition,and drift.The downwash airflow field of the Unmanned Aviation Vehicle(UAV)primarily influences droplet deposition and drift by changing the spray characteristics.This study focused mainly on the effect of the downwash airflow field of the UAV and nozzle position on the droplet spatial distribution and velocity distribution,which are two factors of spray characteristics.To study the abovementioned characteristics,computational fluid dynamics based on the lattice Boltzmann method(LBM)was used to simulate the downwash airflow field of the DJI T30 six-rotor plant protection UAV at different rotor rotational speeds(1000-1800 r/min).A particle image velocimetry system(PIV)was utilized to record the spray field with the downwash airflow field at different rotational speeds of rotors(0-1800 r/min)or different nozzle positions(0,0.20 m,0.35 m,and 0.50 m from the motor).The simulation and experimental results showed that the rotor downwash airflow field exhibited the‘dispersion-shrinkage-redispersion’development rule.In the initial dispersion stage of rotor airflow,there were obvious high-vorticity and low-vorticity regions in the rotor downwash airflow field.Moreover,the low-vorticity region was primarily concentrated below the motor,and the high-vorticity region was mainly focused in the middle area of the rotors.Additionally,the Y-direction airflow velocity fluctuated at 0.4-1.2 m under the rotor.When the rotor airflow developed to 3.2 m below the rotor,the Y-direction airflow velocity showed a slight decrease.Above 3.2 m from the rotor,the Y-direction airflow velocity started to drastically decrease.Therefore,it is recommended that the DJI T30 plant protection UAV should not exceed 3.2 m in flight height during field spraying operations.The rotor downwash airflow field caused the nozzle atomization angle,droplet concentration,and spray field width to decrease while increasing the vortex scale in the spray field when the rotor system was activated.Moreover,the increase in rotor rotational speed promoted the abovementioned trend.When the nozzle was installed in various radial locations below the rotor,the droplet spatial distribution and velocity distribution were completely different.When the nozzle was installed directly below the motor,the droplet spatial distribution and velocity distribution were relatively symmetrical.When the nozzle was installed at 0.20 m and 0.35 m from the motor,the droplets clearly moved toward the right under the induction of stronger rotor vortices.This resulted in a higher droplet concentration in the right-half spray field.However,the droplet moved toward the left when the nozzle was installed in the rotor tip.For four nozzle positions,when the nozzle was installed at 0 or 0.20 m from the motor,the droplet average velocity was much higher.However,the droplet average velocity was slower when the nozzle was installed in the other two positions.Therefore,it is recommended that the nozzle is installed at 0 or 0.20 m from the motor.The research results could increase the understanding of the downwash airflow field distribution characteristics of the UAV and its influence on the droplet spatial distribution and velocity distribution characteristics.Meanwhile,the research results could provide some theoretical guidance for the choice of nozzle position below the rotor.

Spatial distribution visualization of PWM continuous variable-rate spray

Pesticide application is a dynamic spatial distribution process,in which spray liquid should be able to cover the targets with desired thickness and uniformity.Therefore,it is important to study the 2-D and 3-D(dimensional)spray distribution to evaluate spraying quality.The curve-surface generation methods in Excel were used to establish 1-D,2-D,and 3-D graphics of variable-rate spray distribution in order to characterize the space distribution of the variable-rate spray.The 1-D,2-D,and 3-D distribution graphs of Pulse-Width Modulation(PWM)-based continuous variable-rate spray were developed to provide a tool to analyze the distribution characteristics of the spray.The 1-D graph showed that the spray distribution concentrated toward the center of the spray field with the decreased flow-rate.The 2-D graph showed that the spray distribution always spread as the shape of Normal Probability Distribution with the change of the flow-rate.The 3-D graph showed that the spray distribution tended to be uniform when the sprayer travelled forward at the appropriate speed.This study indicated that the visualization method could be directly used for analysis and comparison of different variable-rate spray distributions from different experimental conditions and measuring methods.

Evaluating droplet distribution of spray-nozzles for dust reduction in livestock buildings using machine vision

Previous studies have demonstrated the negative effects of sub-optimal air quality on profitability,production efficiency,environmental sustainability and animal welfare.Experiments were conducted to assess potential environmental improvement techniques such as installing oil-spraying systems in piggery buildings.The developed spray system worked very well and it was easy to assemble and operate.However,before selecting the most suitable spray heads,their capacity to uniformly distribute the oily mixture and the area covered by the spray heads had to be assessed.Machine vision techniques were used to evaluate the ability of different spray heads to evenly distribute the oil/water mixture.The results indicated that the best coverage was achieved by spray head No.4 and spray head No.1 which covered 79%and 67%of the target area,respectively.Spray distribution uniformity(variance)value was the lowest for spray head No.4(0.015).Spray head No.3 had the highest variance value(0.064).As the lowest variance means higher uniformity,nozzle No.4 was identified as the most suitable spray head for dust reduction in livestock buildings.

Droplet size and spray pattern characteristics of PWM-based continuously variable spray

A Pulse-Width-Modulation-based(PWM-based)continuously variable sprayer was developed using a proportional regulating solenoid valve.Variable flow-rate was obtained by varying the duty cycle of the actuating signal with 24 kHz frequency.Flow-rate regulating ranges of the PWM-based continuously variable spray(i.e.the turndown ratio responding to 100%-40%duty cycle)are 7.14:1,3.57:1,and 3.70:1 for flat-fan,hollow-cone and solid-cone nozzles,respectively.The purpose of the study was to evaluate the PWM-based continuously variable spray.The method was to quantify the effects of flow-rate control on spray characteristics in terms of droplet size spectra,spray distribution patterns,and spray angle for flat-fan,hollow-cone,solid-cone nozzles.For all nozzles tested,spray distribution concentrated on the center of the spray field with the decrease of flow-rate.But the spray shape is still symmetrical.The sensitivities of the spray angles to flow-rate were 0.83,0.67,and 0.58(o)/%respectively for flat-fan,hollow-cone and solid-cone nozzles.Compared with the sensitivities of spray angle for PWM-based intermittent variable spray,they are somewhat larger.As flow-rate was reduced from the maximum(100%flow-rate)to the minimum controllable rate,the observed median diameter of spray droplets decreased by 5.4%,9.8%,and 9.9%for flat-fan,hollow-cone and solid-cone nozzles,respectively.This indicates that spray droplet size was affected slightly by flow-rate control.

Mechanistic Insights into Effects of Outer Stage Flare Angle on Ignition and Flame Propagation of Separated Dual-Swirl Spray Flames

The present work investigates the effects of outer stage flare angle on ignition and kernel propagation in a centrally staged optical model combustor based on the kernel dynamics analysis and laser diagnostics of flow and spray fields.Three outer stage flare angles of 8°,16°,and 25°are researched,respectively.The better ignition performances are found for larger outer stage flare angles.Key properties such as the kernel velocity,kernel trajectory extracted from 6 k Hz high-speed flame images are analyzed in combination with the flow and spray measured via Particle Image Velocimetry(PIV)and Planar Mie Scattering(PMie).Results show that the larger outer stage flare angle imposes a larger opening angle of outer swirl jet(SWJ),shifting the vortex in outer recirculation zone(ORZ)and inner recirculation zone(IRZ)upstream.The spray distribution of a smaller flare angle exhibits a fuel-lean zone near the igniter and this is attributed to the presence of low-angle outer swirl jet that prevents the fuel droplets from arriving at the igniter vicinity.The flame kernel propagates along the path where the strain rate and velocity decrease and the spray droplet density is within the flammable limits.A lower outer stage flare angle increases the strain rate and velocity at the early phase of flame propagation,leading to a longer propagation route and thus increasing the risk of ignition failure.

Optimized design and test for a pendulum suspension of the crop spray boom in dynamic conditions based on a six DOF motion simulator

Spray deposit distribution from a field sprayer is mainly affected by the boom movements when the tractor is driven over a rough soil surface,the pendulum suspension that used to reduce and control the movement of spray boom by isolating the boom from vibrations of the tractor will directly enhance uniform deposition of chemicals.However,how to match the parameters of the suspension with the properties of the boom is the key problem.The dynamic rigid-flexible coupling model of the virtual prototype of the spray boom suspension system was established by using ADAMS and ABAQUS software.An optimization of the suspension parameters for a large spay boom was carried out based on the optimal Latin hypercube design,radial basis function neural network,and multi-objective genetic algorithm NSGA-II.After modified parameters of the suspension,the travel of the sprayer on a typical field motion track was simulated based on a six DOF motion simulator,and the dynamic behavior of the boom suspension was measured.The results show that RMS of the measured boom roll angle and the boom center displacement for optimized solution were reduced by 14.76%and 12.43%compared with the original suspension.Finally,the inertial measurement unit(IMU)was used to measure the movements of the sprayer vehicle during the pesticide application on the Hongze Lake Farm,the experiment of field condition reproduced by using the six DOF motion simulator,the standard deviation of the roll angle and vibration displacement for the optimized sprayer boom are only 0.6382°and 62.279 mm respectively.The research provides theoretical basis and experimental method for parameter optimization of large scale boom suspension.