Aerodynamic numerical simulation of four-axis vertical take-off and landing jet unmanned aerial vehicle
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摘要: 基于无人垂直起降飞行器对高机动性、高负载、高动态响应的严苛要求，设计一款四轴垂直起降喷气式无人机. 根据流体力学三大基本方程以及湍流
$ k-\varepsilon $ 方程对气动数值仿真模拟，确定无人机飞行时外部流场计算域. 利用ICEM CFD软件对外部流场进行混合式非结构化网格划分，在Fluent求解器中设置流场边界条件，以湍流模型为基本模型，对无人机整机进行气动性能进行模拟并求解，得到无人机各部分表面的阻力系数、流速分布图、压力分布图和湍流动能图. 对其进行气动特性分析，得出无人机上表面顶部、尾部、下表面头部以及喷气支架处存在动能损耗较大、阻力系数较高的问题. 根据仿真结果，对无人机上述部位进行气动造型优化，结果表明，无人机总阻力系数由原来的0.165减小至0.121，有效改善了无人机表面压力、气流流速和湍流度. 优化后气动特性更加优良，气动造型符合设计理念.Abstract: Based on the strict requirements of high maneuverability, high load and high dynamic response of unmanned vertical take-off and landing (VTOL) aircraft, a four-axis VTOL jet unmanned aerial vehicle (UAV) was researched and designed. According to the three basic equations of fluid mechanics and turbulence k−ε equation, the aerodynamic numerical simulation was carried out to determine the calculation domain of the external flow field during UAV flight. ICEM CFD software was used to divide the external flow field into hybrid unstructured grids. The flow field boundary conditions were set in the Fluent solver, and the turbulence model was taken as the basic model. The aerodynamic performance of the whole UAV were simulated and solved. The resistance coefficient, flow velocity distribution, pressure distribution and turbulent kinetic energy of each part of the UAV surface were obtained, and the aerodynamic characteristics were analyzed. The analysis shows that there are problems of large kinetic energy loss and high resistance coefficient at the top, tail, lower surface head and jet bracket of the upper surface of the UAV. According to the simulation results, the aerodynamic modeling of the above parts of the UAV was optimized. The results show that the total resistance coefficient of the UAV is reduced from the original 0.165 to 0.121, and the surface pressure, flow velocity and turbulence of the UAV are effectively improved. After optimization, the aerodynamic characteristics are better and the aerodynamic modeling is in line with the design concept. -
图 8 无人机造型优化图
1—减小头部上缘迎风面的角度；2—无人机头部采用曲面形式；3—喷气支架采用封闭式设计代替镂空式；4—尾部下缩上缘部分，上下缘都采用曲面过渡.
Figure 8. UAV modeling optimization diagram
表 1 飞行器整机参数
Table 1. Parameters of the aircraft
名称 参数 名称 参数 整机长度/m 1.32 整机质量/kg 20 整机宽度/m 0.73 前进飞行速度/（m∙s−1） 10 整机高度/m 0.32 单个发动机推力/kg 21 导流管旋转角度/（°） 60 有效载物质量/kg 60 最高飞行时间/min 30 上升飞行速度/（m∙s−1） 2 
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表 2 无人机优化前后各表面阻力系数对比
Table 2. Comparison of surface resistance coefficients before and after UAV optimization
仿真设计 头部 机身 尾部 喷管支架 总计 优化前 0.037 0.015 0.04 0.073 0.165 优化后 0.018 0.012 0.031 0.06 0.121 优化比/% 51.35 20 22.5 17.81 26.67
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