植保无人机施药数值建模关键技术与验证方法研究进展

随着植保无人机在精细农业上的应用日益增长，目前在植保无人机下洗风场演化及其作用下的雾滴沉积飘移过程的数值模拟方法取得了快速多样化发展，但对各方法的优势、缺陷、适用范围及验证手段仍缺乏系统的梳理。本文针对无粘模型、计算流体力学模型及格子玻尔兹曼模型分别开展论述。基于涡元法的无粘尾涡模型优势在于计算过程简单，但由于缺乏粘性和湍流模型，其雾滴沉积飘移模拟精度较低。计算流体力学模型又分为有限体积法与有限差分法。其中，有限体积法鲁棒性高，可适用于各种复杂环境的模拟，但格式精度有限，其模拟的翼尖涡耗散速度远快于实际情况；有限差分法能够实现对翼尖涡演化的高时空精度模拟，但其存在网格结构化要求高，算力要求过大等问题。格子玻尔兹曼方法在计算具有复杂边界条件和非平稳运动物体的三维流场问题中具备优势，但其在功能多样性和完备性上还存在不足。上述数值模型精度还需综合运用田间实验及室内实验，如高速粒子图像测速（Particle Image Velocimetry，PIV）或相位多普勒测速（Phase Doppler Interferometry，PDI）方法进行验证和优化。最后，本文提出了未来植保无人机施药模拟及验证方法发展方向。

Research Progress of Key Technologies and Verification Methods of Numerical Modeling for Plant Protection Unmanned Aerial Vehicle Application

With the increasing application of plant protection unmanned aerial vehicle (UAV) in precision agriculture, the numerical simulation methods for the development of the downwash flow field of the plant protection UAV and the deposition and drift process of droplets affected by the downwash flow field have achieved rapid and diversified development, but the advantages, disadvantages, scope of application, and verification of each method still lack a systematic review. This article discusses the inviscid model, computational fluid dynamics model and lattice Boltzmann model (LBM) respectively. The advantage of the inviscid wake vortex model based on the vortex element method is that the calculation process is simple. Moreover, integrated with the most widely used aerial spray drift prediction software AGricultural DISPersal (AGDISP), it can be a promising way to do real-time UAV spray drift prediction. But due to lack of viscosity and turbulence models, the droplet deposition and drift simulation accuracy of inviscid model is relatively lower than other models. The computational fluid dynamics (CFD) model includes the finite volume method (FVM) and the finite difference method (FDM). The FVM in the computational fluid dynamics model has high robustness and can be applied to the simulation of various complex environments. Many commercial CFD software are based on FVM and achieved a fast development in aerial spray modeling recently. However, the FVM is greatly affected by the quality of the mesh, and its commonly used upwind style has limited accuracy (second-order accuracy). Under the same mesh density, it is easier to generate artificial dissipation when simulating the rotor tip vortex than the finite difference method. As a result, the simulated rotor tip vortex dissipation speed is much faster than the actual situation. Compared with the FVM, the structured grid used in the FDM is easier to construct a high-order precision numerical format. Which can reach 4-5 orders of accuracy, and with adaptive grid technology, FDM can simulate the evolution of rotor tip vortex with high temporal and spatial accuracy, and can reproduce the typical flow structure development process of the real rotor downwash flow field. However, it also has problems such as high grid structure requirements and excessive computing power requirements. LBM has advantages in computing three-dimensional flow field problems with complex boundary conditions and non-stationary moving objects. However, there are still shortcomings in its functional diversity and completeness. The accuracy of the numerical models mentioned above still needs field test and indoor experiment such as high-speed Particle Image Velocimetry (PIV)/ Phase Doppler Interferometry (PDI) method to verify and optimize. The authors finally pointed out the future direction of plant protection UAV application simulation and verification.