The temperature distributions on the helicopter airframe and in the exhaust plume are affected seriously by the engine exhaust system, rotor downwash and solar irradiance. To precisely simulate temperature distributio...The temperature distributions on the helicopter airframe and in the exhaust plume are affected seriously by the engine exhaust system, rotor downwash and solar irradiance. To precisely simulate temperature distribution on the helicopter airframe and in the exhaust plume, the effects of rotor downwash and solar irradiance are considered in three-dimensional flow and heat transfer calculation under helicopter hovering. Based on the temperature distribution, a forward-backward ray tracing method is used to calculate the helicopter infrared （IR） radiation intensity. A numerical study is conducted on a fictitious helicopter model with an integrated exhaust system-tail airframe configuration, and the thermal and infrared radiation characteristics are analyzed.展开更多
This paper investigates the influence of forward-swept wing (FSW) positions on the aerodynamic characteristics of aircraft under supersonic condition (Ma = 1.5). The numerical method based on Reynolds-averaged Navier-...This paper investigates the influence of forward-swept wing (FSW) positions on the aerodynamic characteristics of aircraft under supersonic condition (Ma = 1.5). The numerical method based on Reynolds-averaged Navier-Stokes (RANS) equations, Spalart-Allmaras (S-A) turbulence model and implicit algorithm is utilized to simulate the flow field of the aircraft. The aerodynamic parameters and flow field structures of the horizontal tail and the whole aircraft are presented. The results demonstrate that the spanwise flow of FSW flows from the wingtip to the wing root, generating an upper wing surface vortex and a trailing edge vortex nearby the wing root. The vortexes generated by FSW have a strong downwash effect on the tail. The lower the vertical position of FSW, the stronger the downwash effect on tail. Therefore, the effective angle of attack of tail becomes smaller. In addition, the lift coefficient, drag coefficient and lift-drag ratio of tail decrease, and the center of pressure of tail moves backward gradually. For the whole aircraft, the lower the vertical position of FSW, the smaller lift, drag and center of pressure coefficients of aircraft. The closer the FSW moves towards tail, the bigger pitching moment and center of pressure coefficients of the whole aircraft, but the lift and drag characteristics of the horizontal tail and the whole aircraft are basically unchanged. The results have potential application for the design of new concept aircraft. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.展开更多
This paper introduces a semi-empirical model to predict the downwash gradient at the horizontal tail of a three-lifting-surface aircraft.The superposition principle applied to well established formulations valid for t...This paper introduces a semi-empirical model to predict the downwash gradient at the horizontal tail of a three-lifting-surface aircraft.The superposition principle applied to well established formulations valid for two lifting surfaces is not a reasonable approach to calculate the downwash of a canard-wing-tail layout,and this paper demonstrates that such a basic technique leads to incorrect results.Therefore,an ad hoc prediction model is proposed that considers the combined nonlinear effects of canard and main wing inductions on tail downwash,being based on a full factorial design sweep of CFD simulations obtained by varying the main geometrical parameters of the three lifting surfaces.A suitable analytical formula for the downwash gradient is established through a process of data analysis and factor extraction.The presented model extends the validity of the available models for traditional two-lifting-surface designs by means of a correction factor.The engineering estimation method introduced here exhibits an acceptable accuracy,as well as relatively small prediction errors,and it is suitable for conceptual and preliminary studies of threesurface layouts.The value of this methodology is confirmed by the validation with the results of numerical and experimental investigations on a case study aircraft.展开更多
In recent times,the use of vertical take-off and landing(VTOL)multi-rotor Unmanned Aerial Vehicle(UAVs)for spraying chemical pesticides against weeds and pests has recently become popular.The current aerial spray appl...In recent times,the use of vertical take-off and landing(VTOL)multi-rotor Unmanned Aerial Vehicle(UAVs)for spraying chemical pesticides against weeds and pests has recently become popular.The current aerial spray application research is primarily focused on examining the influence of UAV spraying parameters such as flight height,travel speed,rotor configuration,droplet size,payload and wind velocity.The downwash airflow velocity generated by the UAV rotor propeller has a significant impact on the droplet deposition process.A test rig was developed to measure the downwash airflow pattern generated by the rotor propeller of a UAV.In this investigation,a six-rotor electric autonomous UAV sprayer was used to investigate the parameters and distribution laws of downwash airflow velocity.The downwash airflow velocity was measured using portable anemometers mounted on the test rig at radial positions viz.,0 m,0.5 m,1 m,1.5 m and 2 m,perpendicular to(X)and parallel to the UAV’s flight direction(Y).The experiment was conducted at three levels of hover height,viz.,1 m,2 m and 3 m(Z)and three levels of payload,viz.,0 kg,5 kg,and 10 kg.The special downwash airflow distribution pattern was analysed using the Python programming language(Version 3.7).Results show that the downwash airflow velocity generated by the radial position of the UAV rotor is evenly distributed on the rotating loop and the standard deviation of the downwash airflow velocity is less than 0.5 m/s.The maximum downwash airflow velocity of 13.8 m/s was observed below the rotor at 10 kg payload capacity,1 m hover height(Z),and 0.5 m in the X-direction.The minimum downwash wind field of 0.3 m/s was observed at 0 kg pay load capacity,1 m height,and 2 m in the X-direction.The downwash airflow velocity along each position in the radial direction of the rotor increases initially and then decreases.This downwash airflow distribution results helps in mounting of spray nozzle configuration to drone sprayer which helps to understanding spray liquid distribution and other spray operational parameters.The influence of downwash airflow distribution combined with the spray operational parameters of the UAV sprayer viz.,flight height,travel speed,rotor configuration,payload and wind velocity on spray volume distribution was studied.A field experiment was conducted to study the effect of UAV sprayer downwash airflow distribution on spray droplet deposition characteristics in a rice crop compared with manual knapsack sprayer.展开更多
Recently,multi-rotor unmanned aerial vehicle(UAV)becomes more and more significantly irreplaceable in the field of plant protection against diseases,pests and weeds of crops.The easy takeoff and landing performance,ho...Recently,multi-rotor unmanned aerial vehicle(UAV)becomes more and more significantly irreplaceable in the field of plant protection against diseases,pests and weeds of crops.The easy takeoff and landing performance,hover function and high spraying efficiency of UAV are urgently required to spray pesticide for crop timely and effectively,especially in dispersed plots and hilly mountains.In such situations,the current researches about UAV spray application mainly focus on studying the influence of the UAV spraying parameters on the droplet deposition,such as operation height,operation velocity and wind velocity.The deposition and distribution of pesticide droplets on crops which depends on installation position of nozzle and airflow distribution characteristics of UAV are directly related to the control effect of pesticide and crop growth in different growth periods.As a preliminary step,this study focuses on the dynamic development law and distribution characteristics of the downwash air flow for the SLK-5 six-rotor agricultural UAV.Based on compressible Reynolds-averaged Navier-Stokes(RANS)equations with an RNG k-εturbulence model and dynamic mesh technology,the efficient three-dimensional computational fluid dynamics(CFD)method was established to analyze the flow field distribution characteristics of UAV in hover.Then the unsteady interaction flow field of the wing was investigated in detail.The downwash wind speed of the marked points for the SLK-5 UAV in hover was also tested by weather tracker.It was found that the maximum velocity value of the downwash flow was close to 10 m/s;the z-direction velocity was the main body of the wind velocity in the downwash airflow,and the comparison of the wind velocity experiment test and simulation showed that the relative error was less than 12%between the experimental and simulated values of the z-direction velocity at the marked points.Then the flow characteristics of the longitudinal and cross section were analyzed in detail,the results obtained can be used as a reference for drift and sedimentation studies for multi-rotor unmanned aerial vehicle.展开更多
The effective coverage and velocity of downwash are directly related to the assemblage of spraying system and spraying effect.The downwash of the unmanned agricultural helicopter(UAH)N-3 was discussed in the paper.The...The effective coverage and velocity of downwash are directly related to the assemblage of spraying system and spraying effect.The downwash of the unmanned agricultural helicopter(UAH)N-3 was discussed in the paper.The computational fluid dynamics(CFD)methods were used to simulate and analyze the distribution of the downwash,and a wind field measurement device had been designed to test the downwash of UAH N-3.In the tests,the UAH N-3 was raised up to 5.0 m,6.0 m and 7.0 m from the ground,“annular-radial-distribution-point”method was introduced,8 directions separated by an angle of 45°(the radial direction)with the intersection point of the main rotor shaft and the ground plane as the center,0.5 m as the step length for the longitudinal(to 2.5 m)and radial(to 4.0 m)direction to set the sample points,considering the range of the rotor rotating circular area mainly.The 5 m height results of N-3 were fully discussed to describe the downwash distribution with the longitudinal altitude increased and the radial distance increased.The standard deviations of five test altitudes for eight directions were comparatively analyzed,the results showed that the total standard deviation was not greater than 0.6 m/s.The overall relative maximum margin of error calculated from the simulation and measurement data was between 0.6 and 0.7,which verified the credibility of the simulation data.High-order polynomials were used to fitting the simulation and measurement data,the fitting results showed that the polynomial coefficient of determination R^(2) met or exceeded 0.75 when the altitudes were more than 1 m,indicating the fit equation having the reference values.When the altitudes equal or less than 0.5 m,the polynomial coefficient of determination R^(2) was smaller,ranging during 0.3 to 0.7.The study would provide some foundations for the optimization of the assemblage of spraying system on the single-rotor UAH,which would promote China aviation plant protection.展开更多
The downwash flow field of the multi-rotor unmanned aerial vehicle(UAV), formed by propellers during operation, has a significant influence on the deposition, drift and distribution of droplets as well as the spray wi...The downwash flow field of the multi-rotor unmanned aerial vehicle(UAV), formed by propellers during operation, has a significant influence on the deposition, drift and distribution of droplets as well as the spray width of the UAV for plant protection. To study the general characteristics of the distribution of the downwash airflow and simulate the static wind field of multi-rotor UAVs in hovering state, a 3 D full-size physical model of JF01-10 six-rotor plant protection UAV was constructed using Solid Works. The entire flow field surrounding the UAV and the rotation flow fields around the six rotors were established in UG software. The physical model and flow fields were meshed using unstructured tetrahedral elements in ANSYS software.Finally, the downwash flow field of UAV was simulated.With an increased hovering height, the ground effect was reduced and the minimum current velocity increased initially and then decreased. In addition, the spatial proportion of the turbulence occupied decreased. Furthermore, the appropriate operational hovering height for the JF01-10 is considered to be 3 m. These results can be applied to six-rotor plant protection UAVs employed in pesticide spraying and spray width detection.展开更多
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,c...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 RNGκ-εas 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.展开更多
The downwash airflow field is an important factor influencing the spraying performance of plant protection UAV,and the structural design of rotors directly affects the characteristics of the downwash airflow field.The...The downwash airflow field is an important factor influencing the spraying performance of plant protection UAV,and the structural design of rotors directly affects the characteristics of the downwash airflow field.Therefore,in this study,three-dimensional models of a six-rotor UAV with various inner tilt angles were established to simulate and analyze the influence of the inner tilt angle on the downwash airflow field based on the Reynolds average NS equation,RNG k-εturbulence model,etc..On this basis,a wireless wind speed acquisition system using the TCP server was developed to carry out the test through the marked points with real-time detection.The simulation results show that,the variation of inner tilt angles of the six-rotor UAV did not cause significant difference in the time dimension of the downwash airflow field,and with the change of the inner tilt angle from 0°to 8°,the distribution of downwash airflow field tended to obliquely shrink towards the central axis direction,and the amplitude of linear attenuation of airflow speed was also increased,which the difference of attenuation amplitude was 1 m/s.Besides,under the different inner tilt angle,the airflow velocity in“lead in area”was significantly greater than that in the“lead out area”,and the difference of air velocity distribution in space would affect the uniformity of droplet deposition.Through the calibration test,the measurement accuracy error of the developed system was lower than 0.3 m/s,and the adjusted R2 of the calibration fitting equation was higher than 0.99.The test and simulation values at test points from 0.2-2.3 m below the rotors exhibit the same variation trend,and the average relative error at the height of 1.1-2.3 m below the rotors and 0.2-0.8 m near the ground was within 10%and 20%,respectively.The simulation and test results were highly reliable,which could provide basis and reference for the design and optimization of plant protection drones.展开更多
Currently,Computational Fluid Dynamics(CFD)has been used to investigate agricultural UAV downwash.However,the validations of CFD models are difficult to deal with.Current verification methods are to use either water-s...Currently,Computational Fluid Dynamics(CFD)has been used to investigate agricultural UAV downwash.However,the validations of CFD models are difficult to deal with.Current verification methods are to use either water-sensitive papers or wind-speed arrays,which could get wind distribution or speed only.In this study,model migration was used to develop and verify downwash CFD models.The basic idea is to try to use the results of a scaled-down drone to represent that of a real-used UAV.The CFD models of both a real-used six-rotor UAV,JF01-10,and a 1:10 scaled-down small drone were developed by ANSYS.Then,the scaled-down drone was utilized to conduct trials by particle image velocimetry(PIV),so that not only distribution and speed but also flowing direction of downwash could be obtained.Results indicated the relative error between the PIV tests and the CFD models of the small UAV was less than 12%,while that between the tests and the CFD models of JF01-10 was less than 34%.It could be indicated that model migration could reflect multiple downwash characteristics but should be optimized in some complex details.This study was a preliminary but fundamental attempt to investigate CFD modelling and validation of agricultural UAVs and provided a novel thinking of downwash verification.展开更多
In recent years,multi-rotor Unmanned Aerial Vehicles(UAVs)have been employed in the field of plant protection in China.Spray drift has been considered a major impact in agriculture aerial spraying,and spray quality in...In recent years,multi-rotor Unmanned Aerial Vehicles(UAVs)have been employed in the field of plant protection in China.Spray drift has been considered a major impact in agriculture aerial spraying,and spray quality in the application of plant protection products.The downwash including wake vortices and downward wind field plays a major role in the dispersal and deposition of pesticide spray released by nozzle(s)equipped in aircraft.Differ from the fixed-wing UAV,the downwash flow of multi-rotor UAV was result from the rotation of rotor.Therefore,a study on off-target drift and ground deposit concerning the rotor rotation was simulated through a series of Computational Fluid Dynamics(CFD)simulations to obtain the influence of downwash.The discrete Phase Model(DPM)was taken to simulate the motion of droplet particles since it is an appropriate way to simulate discrete phases in flow field and can track particle trajectory.In this study,the parameters of CFD simulations were acquired by three kinds of actual replicated experiment.The simulation analysis mainly obtains the droplet drift and deposition rule,the influence of eddy current,and downwash flow caused by the rotor rotation.The results showed that the downwash distribution below different rotors was different owing to the flight angle of inclination,“behind”is the greatest,“middle”is secondly,and“forward”is smallest in value(behind,middle,and forward represent three regions below rotors along flight direction).According to the simulation results,two methods of reducing droplet drift were put forward and specific simulations were carried out to prove their feasibility.The results of this study can provide theoretical support for improving the spray quality of UAV and reducing the drift of droplets.展开更多
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 depositio...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.展开更多
This paper presents a novel solution to the three-dimensional (3D) cooperative hunting ofmultiple drones that deals with surrounding a target simultaneously while navigating aroundobstacles in the cluttered dynamic 3D...This paper presents a novel solution to the three-dimensional (3D) cooperative hunting ofmultiple drones that deals with surrounding a target simultaneously while navigating aroundobstacles in the cluttered dynamic 3D environment. Meanwhile, drones avoid the air°owdownwash force created by the spinning propellers on unmanned aerial vehicles (UAVs) andtheir e®ect on the other UAVs. This solution consists of a 3D Simultaneous Encirclementstrategy, the cooperative hunting objective with a novel revised particle swarm optimization(PSO*) path planning algorithm, a °ocking theory-inspired obstacle avoidance algorithm, and acascade PI controller. Simulation results with varying conditions were carried out to validatethe e®ectiveness of the proposed solution by successfully taking care of the downwash e®ects,and having multiple hunter UAVs hunt and encircle a moving or stationary target in a dynamicor static obstacle-rich cluttered environment.展开更多
文摘The temperature distributions on the helicopter airframe and in the exhaust plume are affected seriously by the engine exhaust system, rotor downwash and solar irradiance. To precisely simulate temperature distribution on the helicopter airframe and in the exhaust plume, the effects of rotor downwash and solar irradiance are considered in three-dimensional flow and heat transfer calculation under helicopter hovering. Based on the temperature distribution, a forward-backward ray tracing method is used to calculate the helicopter infrared （IR） radiation intensity. A numerical study is conducted on a fictitious helicopter model with an integrated exhaust system-tail airframe configuration, and the thermal and infrared radiation characteristics are analyzed.
文摘This paper investigates the influence of forward-swept wing (FSW) positions on the aerodynamic characteristics of aircraft under supersonic condition (Ma = 1.5). The numerical method based on Reynolds-averaged Navier-Stokes (RANS) equations, Spalart-Allmaras (S-A) turbulence model and implicit algorithm is utilized to simulate the flow field of the aircraft. The aerodynamic parameters and flow field structures of the horizontal tail and the whole aircraft are presented. The results demonstrate that the spanwise flow of FSW flows from the wingtip to the wing root, generating an upper wing surface vortex and a trailing edge vortex nearby the wing root. The vortexes generated by FSW have a strong downwash effect on the tail. The lower the vertical position of FSW, the stronger the downwash effect on tail. Therefore, the effective angle of attack of tail becomes smaller. In addition, the lift coefficient, drag coefficient and lift-drag ratio of tail decrease, and the center of pressure of tail moves backward gradually. For the whole aircraft, the lower the vertical position of FSW, the smaller lift, drag and center of pressure coefficients of aircraft. The closer the FSW moves towards tail, the bigger pitching moment and center of pressure coefficients of the whole aircraft, but the lift and drag characteristics of the horizontal tail and the whole aircraft are basically unchanged. The results have potential application for the design of new concept aircraft. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.
基金funded for the development of an innovative high-capacity regional turboprop platform by the IRON projectreceived funding from the Clean Sky 2 Joint Undertaking under the European Union's Horimpzon 2020 research and innovation program under Grant Agreement No.699715part of Clean Sky 2 REG-GAM 2018 project implemented on the H2020 program under GA 807089。
文摘This paper introduces a semi-empirical model to predict the downwash gradient at the horizontal tail of a three-lifting-surface aircraft.The superposition principle applied to well established formulations valid for two lifting surfaces is not a reasonable approach to calculate the downwash of a canard-wing-tail layout,and this paper demonstrates that such a basic technique leads to incorrect results.Therefore,an ad hoc prediction model is proposed that considers the combined nonlinear effects of canard and main wing inductions on tail downwash,being based on a full factorial design sweep of CFD simulations obtained by varying the main geometrical parameters of the three lifting surfaces.A suitable analytical formula for the downwash gradient is established through a process of data analysis and factor extraction.The presented model extends the validity of the available models for traditional two-lifting-surface designs by means of a correction factor.The engineering estimation method introduced here exhibits an acceptable accuracy,as well as relatively small prediction errors,and it is suitable for conceptual and preliminary studies of threesurface layouts.The value of this methodology is confirmed by the validation with the results of numerical and experimental investigations on a case study aircraft.
文摘In recent times,the use of vertical take-off and landing(VTOL)multi-rotor Unmanned Aerial Vehicle(UAVs)for spraying chemical pesticides against weeds and pests has recently become popular.The current aerial spray application research is primarily focused on examining the influence of UAV spraying parameters such as flight height,travel speed,rotor configuration,droplet size,payload and wind velocity.The downwash airflow velocity generated by the UAV rotor propeller has a significant impact on the droplet deposition process.A test rig was developed to measure the downwash airflow pattern generated by the rotor propeller of a UAV.In this investigation,a six-rotor electric autonomous UAV sprayer was used to investigate the parameters and distribution laws of downwash airflow velocity.The downwash airflow velocity was measured using portable anemometers mounted on the test rig at radial positions viz.,0 m,0.5 m,1 m,1.5 m and 2 m,perpendicular to(X)and parallel to the UAV’s flight direction(Y).The experiment was conducted at three levels of hover height,viz.,1 m,2 m and 3 m(Z)and three levels of payload,viz.,0 kg,5 kg,and 10 kg.The special downwash airflow distribution pattern was analysed using the Python programming language(Version 3.7).Results show that the downwash airflow velocity generated by the radial position of the UAV rotor is evenly distributed on the rotating loop and the standard deviation of the downwash airflow velocity is less than 0.5 m/s.The maximum downwash airflow velocity of 13.8 m/s was observed below the rotor at 10 kg payload capacity,1 m hover height(Z),and 0.5 m in the X-direction.The minimum downwash wind field of 0.3 m/s was observed at 0 kg pay load capacity,1 m height,and 2 m in the X-direction.The downwash airflow velocity along each position in the radial direction of the rotor increases initially and then decreases.This downwash airflow distribution results helps in mounting of spray nozzle configuration to drone sprayer which helps to understanding spray liquid distribution and other spray operational parameters.The influence of downwash airflow distribution combined with the spray operational parameters of the UAV sprayer viz.,flight height,travel speed,rotor configuration,payload and wind velocity on spray volume distribution was studied.A field experiment was conducted to study the effect of UAV sprayer downwash airflow distribution on spray droplet deposition characteristics in a rice crop compared with manual knapsack sprayer.
基金acknowledge the financial support provided by the National Key Research and Development Plan of China(No.2016YFD0200702)Study on Key Techniques of Aviation Plant Protection for Rice Diseases and Insect Pests of China(No.S201729)+1 种基金Open exchange project of China-US pesticide technology Joint Research Center(No.Y2017PT32)Aviation intelligent pesticide operation system based on Beidou automatic navigation(No.S201609).
文摘Recently,multi-rotor unmanned aerial vehicle(UAV)becomes more and more significantly irreplaceable in the field of plant protection against diseases,pests and weeds of crops.The easy takeoff and landing performance,hover function and high spraying efficiency of UAV are urgently required to spray pesticide for crop timely and effectively,especially in dispersed plots and hilly mountains.In such situations,the current researches about UAV spray application mainly focus on studying the influence of the UAV spraying parameters on the droplet deposition,such as operation height,operation velocity and wind velocity.The deposition and distribution of pesticide droplets on crops which depends on installation position of nozzle and airflow distribution characteristics of UAV are directly related to the control effect of pesticide and crop growth in different growth periods.As a preliminary step,this study focuses on the dynamic development law and distribution characteristics of the downwash air flow for the SLK-5 six-rotor agricultural UAV.Based on compressible Reynolds-averaged Navier-Stokes(RANS)equations with an RNG k-εturbulence model and dynamic mesh technology,the efficient three-dimensional computational fluid dynamics(CFD)method was established to analyze the flow field distribution characteristics of UAV in hover.Then the unsteady interaction flow field of the wing was investigated in detail.The downwash wind speed of the marked points for the SLK-5 UAV in hover was also tested by weather tracker.It was found that the maximum velocity value of the downwash flow was close to 10 m/s;the z-direction velocity was the main body of the wind velocity in the downwash airflow,and the comparison of the wind velocity experiment test and simulation showed that the relative error was less than 12%between the experimental and simulated values of the z-direction velocity at the marked points.Then the flow characteristics of the longitudinal and cross section were analyzed in detail,the results obtained can be used as a reference for drift and sedimentation studies for multi-rotor unmanned aerial vehicle.
基金gratefully acknowledge the National Natural Science Foundation of China(No.31701327)the National Key Research and Development Program of China(No.2017YFD0701000)+1 种基金the Natural Science Foundation of Jiangsu Province,China(BK 20151074)part of the National Key Research and Development Plan:High Efficient Ground and Aerial Spraying Technology and Intelligent Equipment(Grant No.2016YFD0200700).
文摘The effective coverage and velocity of downwash are directly related to the assemblage of spraying system and spraying effect.The downwash of the unmanned agricultural helicopter(UAH)N-3 was discussed in the paper.The computational fluid dynamics(CFD)methods were used to simulate and analyze the distribution of the downwash,and a wind field measurement device had been designed to test the downwash of UAH N-3.In the tests,the UAH N-3 was raised up to 5.0 m,6.0 m and 7.0 m from the ground,“annular-radial-distribution-point”method was introduced,8 directions separated by an angle of 45°(the radial direction)with the intersection point of the main rotor shaft and the ground plane as the center,0.5 m as the step length for the longitudinal(to 2.5 m)and radial(to 4.0 m)direction to set the sample points,considering the range of the rotor rotating circular area mainly.The 5 m height results of N-3 were fully discussed to describe the downwash distribution with the longitudinal altitude increased and the radial distance increased.The standard deviations of five test altitudes for eight directions were comparatively analyzed,the results showed that the total standard deviation was not greater than 0.6 m/s.The overall relative maximum margin of error calculated from the simulation and measurement data was between 0.6 and 0.7,which verified the credibility of the simulation data.High-order polynomials were used to fitting the simulation and measurement data,the fitting results showed that the polynomial coefficient of determination R^(2) met or exceeded 0.75 when the altitudes were more than 1 m,indicating the fit equation having the reference values.When the altitudes equal or less than 0.5 m,the polynomial coefficient of determination R^(2) was smaller,ranging during 0.3 to 0.7.The study would provide some foundations for the optimization of the assemblage of spraying system on the single-rotor UAH,which would promote China aviation plant protection.
基金supported and funded by The National Key Research and Development Program of China (2016YFD02 00700) from China Ministry of Science and TechnologyThe Fundamental Research Funds for the Central Universities (2015TC036 and 2017QC139)
文摘The downwash flow field of the multi-rotor unmanned aerial vehicle(UAV), formed by propellers during operation, has a significant influence on the deposition, drift and distribution of droplets as well as the spray width of the UAV for plant protection. To study the general characteristics of the distribution of the downwash airflow and simulate the static wind field of multi-rotor UAVs in hovering state, a 3 D full-size physical model of JF01-10 six-rotor plant protection UAV was constructed using Solid Works. The entire flow field surrounding the UAV and the rotation flow fields around the six rotors were established in UG software. The physical model and flow fields were meshed using unstructured tetrahedral elements in ANSYS software.Finally, the downwash flow field of UAV was simulated.With an increased hovering height, the ground effect was reduced and the minimum current velocity increased initially and then decreased. In addition, the spatial proportion of the turbulence occupied decreased. Furthermore, the appropriate operational hovering height for the JF01-10 is considered to be 3 m. These results can be applied to six-rotor plant protection UAVs employed in pesticide spraying and spray width detection.
基金This study was sponsored by Heilongjiang Province Conservation Tillage Technology Research CenterHainan Province Natural Science Foundation Program:Study on sedimentation mechanism of pesticide droplets in the chemical borer of sugarcane in single rotor UAV(Grant No.519MS097)+1 种基金Postgraduate research Innovation Project of Heilongjiang Bayi Agricultural University(Grant No.YJSCX2015-Z02)Innovation Team Project of Whole Mechanized Cultivation Techniques in Plant Bowl Breeding(Grant No.2014TD010).
文摘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 RNGκ-εas 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.
基金supported by National Natural Science Foundation of China(Grant No.31801783).
文摘The downwash airflow field is an important factor influencing the spraying performance of plant protection UAV,and the structural design of rotors directly affects the characteristics of the downwash airflow field.Therefore,in this study,three-dimensional models of a six-rotor UAV with various inner tilt angles were established to simulate and analyze the influence of the inner tilt angle on the downwash airflow field based on the Reynolds average NS equation,RNG k-εturbulence model,etc..On this basis,a wireless wind speed acquisition system using the TCP server was developed to carry out the test through the marked points with real-time detection.The simulation results show that,the variation of inner tilt angles of the six-rotor UAV did not cause significant difference in the time dimension of the downwash airflow field,and with the change of the inner tilt angle from 0°to 8°,the distribution of downwash airflow field tended to obliquely shrink towards the central axis direction,and the amplitude of linear attenuation of airflow speed was also increased,which the difference of attenuation amplitude was 1 m/s.Besides,under the different inner tilt angle,the airflow velocity in“lead in area”was significantly greater than that in the“lead out area”,and the difference of air velocity distribution in space would affect the uniformity of droplet deposition.Through the calibration test,the measurement accuracy error of the developed system was lower than 0.3 m/s,and the adjusted R2 of the calibration fitting equation was higher than 0.99.The test and simulation values at test points from 0.2-2.3 m below the rotors exhibit the same variation trend,and the average relative error at the height of 1.1-2.3 m below the rotors and 0.2-0.8 m near the ground was within 10%and 20%,respectively.The simulation and test results were highly reliable,which could provide basis and reference for the design and optimization of plant protection drones.
基金The authors acknowledge that this work was financially supported by the National Key Research and Development Program of China(2018YFD0700603 and 2016YFD0200702)National Natural Science Foundation of China(31701315)+1 种基金Independent Innovation Foundation for the Graduates of China Agricultural University(2020XYZC38A)Chinese Universities Scientific Fund(2020TC116).The devices used in the paper were supported by National Research Center of Intelligent Equipment for Agriculture.
文摘Currently,Computational Fluid Dynamics(CFD)has been used to investigate agricultural UAV downwash.However,the validations of CFD models are difficult to deal with.Current verification methods are to use either water-sensitive papers or wind-speed arrays,which could get wind distribution or speed only.In this study,model migration was used to develop and verify downwash CFD models.The basic idea is to try to use the results of a scaled-down drone to represent that of a real-used UAV.The CFD models of both a real-used six-rotor UAV,JF01-10,and a 1:10 scaled-down small drone were developed by ANSYS.Then,the scaled-down drone was utilized to conduct trials by particle image velocimetry(PIV),so that not only distribution and speed but also flowing direction of downwash could be obtained.Results indicated the relative error between the PIV tests and the CFD models of the small UAV was less than 12%,while that between the tests and the CFD models of JF01-10 was less than 34%.It could be indicated that model migration could reflect multiple downwash characteristics but should be optimized in some complex details.This study was a preliminary but fundamental attempt to investigate CFD modelling and validation of agricultural UAVs and provided a novel thinking of downwash verification.
基金This work was partially financially supported by the National Key R&D Program of China(Grant No.2016YFD0200701).
文摘In recent years,multi-rotor Unmanned Aerial Vehicles(UAVs)have been employed in the field of plant protection in China.Spray drift has been considered a major impact in agriculture aerial spraying,and spray quality in the application of plant protection products.The downwash including wake vortices and downward wind field plays a major role in the dispersal and deposition of pesticide spray released by nozzle(s)equipped in aircraft.Differ from the fixed-wing UAV,the downwash flow of multi-rotor UAV was result from the rotation of rotor.Therefore,a study on off-target drift and ground deposit concerning the rotor rotation was simulated through a series of Computational Fluid Dynamics(CFD)simulations to obtain the influence of downwash.The discrete Phase Model(DPM)was taken to simulate the motion of droplet particles since it is an appropriate way to simulate discrete phases in flow field and can track particle trajectory.In this study,the parameters of CFD simulations were acquired by three kinds of actual replicated experiment.The simulation analysis mainly obtains the droplet drift and deposition rule,the influence of eddy current,and downwash flow caused by the rotor rotation.The results showed that the downwash distribution below different rotors was different owing to the flight angle of inclination,“behind”is the greatest,“middle”is secondly,and“forward”is smallest in value(behind,middle,and forward represent three regions below rotors along flight direction).According to the simulation results,two methods of reducing droplet drift were put forward and specific simulations were carried out to prove their feasibility.The results of this study can provide theoretical support for improving the spray quality of UAV and reducing the drift of droplets.
基金financially supported by the 111 Project(Grant No.D18019)Laboratory of Lingnan Modern Agriculture Project(Grant No.NT2021009)+4 种基金the Leading Talents of Guangdong Province Program(Grant No.2016LJ06G689)the National Natural Science Foundation of China(Grant No.32271985)the Natural Science Foundation of Guangdong Province(Grant No.2022A 1515011008No.2022A1515011535)Liaoning Provincial Education Department Key Research Project(Grant No.LSNZD 202005).
文摘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.
文摘This paper presents a novel solution to the three-dimensional (3D) cooperative hunting ofmultiple drones that deals with surrounding a target simultaneously while navigating aroundobstacles in the cluttered dynamic 3D environment. Meanwhile, drones avoid the air°owdownwash force created by the spinning propellers on unmanned aerial vehicles (UAVs) andtheir e®ect on the other UAVs. This solution consists of a 3D Simultaneous Encirclementstrategy, the cooperative hunting objective with a novel revised particle swarm optimization(PSO*) path planning algorithm, a °ocking theory-inspired obstacle avoidance algorithm, and acascade PI controller. Simulation results with varying conditions were carried out to validatethe e®ectiveness of the proposed solution by successfully taking care of the downwash e®ects,and having multiple hunter UAVs hunt and encircle a moving or stationary target in a dynamicor static obstacle-rich cluttered environment.
