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 refere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
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.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
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 refere
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.
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.
