大载荷农用无人机旋翼风场扰流装置设计与试验

Design and Verification of Wind Field Damping Devices for Large-load Agricultural Unmanned Aerial Vehicles

摘要:

为解决大载荷农用无人机作业过程中因旋翼下洗风场过强易损伤作物,进而导致飞行高度升高、雾滴漂移加剧的问题,设计了一种可有效降低下洗气流速度的扰流装置。以自主研发的无人机为试验平台,结合自研风速传感器与计算流体力学仿真技术(Computational fluid dynamics, CFD),对扰流装置在不同参数下的风场削弱效果进行定量测试与分析,确定了扰流装置的最优参数组合,有效验证了其在削弱旋翼下洗气流方面的工程可行性与技术优势,并针对其参数选取制定了科学、可行的技术方案。首先基于扰流装置的工作原理,结合空气动力学、动量理论及牛顿第三定律等基本物理模型,确定扰流装置的关键参数类型;其次,根据无人机工作状态时下洗风场的轨迹线云图与速度云图,明确各参数变量的梯度变化范围;然后,通过计算流体力学(CFD)仿真与正交试验相结合的方法,综合分析并优化得出各参数的最佳取值。随后,对各关键参数进行多变量耦合分析与优化设计,获得了最优参数组合;最后,通过机载飞行试验对扰流装置的稳定性和有效性进行了验证。正交试验结果表明,安装扰流装置后,风场优化效果与拉力损失率的比值约为9.7,表明该装置在有效削弱下洗气流的同时,对升力性能的影响较小。飞行试验表明,安装扰流装置后无人机拉力损失约10% ,风场平均风速减小了约38.6%,风场优化效果较好。且无人机安装扰流装置后飞行稳定。

Abstract:

Aiming to address the issue of crop damage caused by the strong downwash airflow from the rotors during the operation of heavy-load agricultural drones, which leads to increased flight altitude and intensified droplet drift, a turbulence device that can effectively reduce the downwash airflow velocity was designed. Based on the self-developed unmanned aerial vehicle ( UAV) in the laboratory as the test platform, combined with the self-developed wind speed sensor and computational fluid dynamics (CFD) simulation technology, the weakening effect of the flow deflector on the wind field under different structural parameters was quantitatively tested and analyzed. The optimal parameter combination of the turbulence device was determined, effectively verifying its engineering feasibility and technical advantages in weakening the rotor downwash airflow. The research results can provide theoretical support and experimental basis for the practical application of the turbulence device on heavy-load agricultural UAVs, and a scientific and feasible technical solution for parameter matching and selection was formulated. Firstly, the key parameter types of the turbulence device were screened and determined based on its working principle, together with basic physical models including aerodynamics, momentum theory, and Newton??s third law. Secondly, according to the trajectory line cloud map and velocity cloud map of the downwash wind field under the working state of the UAV, the gradient change range of each parameter variable was reasonably clarified. Then through the combination of CFD simulation and orthogonal experiments, the optimal values of each parameter were comprehensively analyzed and optimized. Subsequently, by combining CFD simulation and orthogonal experiments, a multi-variable coupling analysis and optimization design of each key parameter was conducted, and the optimal parameter combination was obtained. Finally, the stability and effectiveness of the turbulence device were verified through on-board flight tests. The results of the orthogonal experiments showed that the ratio of the wind field optimization effect to the thrust loss rate after installing the turbulence device was approximately 9.7, indicating that the device effectively weakened the downwash airflow while having a relatively small impact on lift performance. Flight tests showed that after installing the flow deflector, the thrust of the UAV was increased by approximately 10.8% , and the average wind speed of the wind field was decreased by approximately 38.6% , demonstrating a good wind field optimization effect. Moreover, the UAV with the turbulence device installed flies stably and had good compatibility with the flight control system of the UAV, fully meeting the overall design requirements of agricultural operation.