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
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
文摘三相分离旋流器是一种用于油田三元采出液气液固三相分离的新型旋流器。基于计算流体动力学(Computational fluid dynamics,CFD)软件Fluent,采用雷诺应力模型(Reynolds stress model,RSM),开展不同采出液混合液相黏度变化对气液固三相分离旋流器速度场、压力特性和脱气除砂效果影响的数值模拟对比分析。研究结果表明:在黏度不大于6.42 m Pa·s时,旋流器受黏度增大的影响,切向速度幅值成降低趋势,切向速度均值降低12.4%,整体上,在研究范围内,该结构旋流器速度场受黏度变化影响相对较小;在黏度不大于6.42 m Pa·s时,旋流器脱气效率和除砂效率均高于80%,旋流器脱气效率最高可达95.97%、对应除砂效率95.19%;研究范围内,混合液黏度变化对旋流器压力降影响较大。随着黏度增加,旋流器溢流压力降逐渐减小、底流压力降逐渐增加。根据相似参数准则,制作了旋流器试验样机,并开展了现场采出液室内试验。模拟与试验结果吻合良好,从而验证了模拟计算结果的可靠性。研究可对适合高黏度介质分离三相分离旋流器的设计提供参考。
