基于Porous模型的多旋翼植保无人机下洗气流分布研究  

Spatio-temporal Distribution of Down-wash Airflow for Multi-rotor Plant Protection UAV Based on Porous Model

作　　者：张豪 祁力钧[1] 吴亚垒 刘婠婠 程浈浈 MUSIU E ZHANG Hao;QI Lijun;WU Yalei;LIU Wanwan;CHENG Zhenzhen(College of Engineering,China Agricultural University,Beijing 100083,China)

机构地区：[1]中国农业大学工学院,北京100083

出　　处：《农业机械学报》2019年第2期112-122,共11页Transactions of the Chinese Society for Agricultural Machinery

基　　金：国家重点研发计划项目(2017YFD0701400;2016YFD0200700)

摘　　要：植保无人机进行果树施药时,果树冠层周围及内部的下洗气流时空分布对雾滴的附着和分布有重大影响,为明确无人机下洗气流时空分布规律,针对六旋翼植保无人机,结合RANS方程、RNG k-ε湍流模型、Porous模型、滑移网格技术及SIMPLE算法,建立了六旋翼植保无人机悬停施药下洗气流时空分布的三维CFD模型。数值模拟结果表明:无果树时,旋翼下洗气流近似呈"圆柱形"向下发展,到达地面后形成地面铺展,在旋翼正下方0. 6～1. 7 m区域内出现速度范围为3. 0～4. 0 m/s的"Z方向(竖直向下)速度稳定区";有果树时,冠层对旋翼下洗气流有明显的阻挡作用,不再出现"Z方向速度稳定区"。以本文模拟的3棵果树为例,Ⅰ号果树冠层周围气流从冠层上半部区域开始呈"圆锥形"向下发展,以一倾斜角发展到地面形成小范围地面铺展,地面铺展末端出现近地面卷扬,Ⅱ、Ⅲ号果树冠层周围气流卷扬严重,在计算区域内无明显地面铺展;旋翼中心正下方Z方向速度最大接近8 m/s,随着冠层压力损失系数的增大,旋翼中心正下方Z方向速度衰减加快,同时旋翼气流向四周产生扩散;计算冠层内部Z方向最大速度衰减比发现,除Ⅲ号果树冠层下半部,无果树和Ⅰ、Ⅱ、Ⅲ号果树冠层内部Z方向最大速度衰减比依次增大。试验表明,无果树时旋翼正下方0. 3、0. 8、1. 3、1. 8 m处和近地面2. 3 m处试验值与模拟值的相对误差分别在10%以内和不大于25%,总体拟合优度0. 984 6,数值模拟准确;试验果树与模拟果树冠层内部的气流速度分布规律具有很好的一致性。When the plant protection UAV is used to spray pesticides on orchard,the spatio-temporal distribution of down-wash airflow inside and around the canopy has a major impact on the adhesion and distribution of the droplets.In order to clarify the spatio-temporal distribution of down-wash airflow inside and around the canopy of trees when applying multi-rotor plant protection UAV to spraying,combining RANS equation,RNG kεturbulence model,porous model,sliding mesh technology and SIMPLE algorithm,a three-dimensional CFD model for the spatio-temporal distribution of the down-wash airflow of six-rotor plant protection UAV in hover was established.The results of numerical simulation showed that when without tree,the down-wash airflow of the rotor developed downward was approximately in a“cylindrical”shape,and formed the ground spreading after reached the ground,and the“Z-direction(vertically downward)speed stable region”appeared in the region of 0.6~1.7 m below the rotor,where the speed range was from 3.0 m/s to 4.0 m/s.When tree existed,the canopy had an obvious effect on blocking the down-wash airflow of the rotor,and it would not appear“Z-direction speed stable zone”.Taking the three trees simulated as an example,the airflow around the canopy of No.Ⅰtree began to develop downward from the upper part of the canopy in a“conical”shape,and developed to the ground at an inclined angle to form a small area of ground spread.There was a near-ground hoisting at the end of the ground spread.The airflow around the canopy of No.Ⅱand No.Ⅲtrees was heavily hoisted,and it did not have obvious ground spread in the calculation area;the maximum speed in Z direction was close to 8 m/s directly below the rotor center.With the increase of canopy pressure loss coefficient,the speed attenuation in Z direction was accelerated,while the rotor airflow was spreaded around.Calculating the maximum speed decay ratio in Z direction inside the canopy,it was found that the maximum speed decay ratio in Z direction in the canopy o

关 键 词：Porous模型 植保无人机 数值模拟 下洗气流 时空分布 

分 类 号：S49[农业科学—植物保护] S252