定桨距共轴双旋翼无人机桨盘干扰气动分析

Aerodynamic Interference Analysis of Rotor Disks for a Fixed-Pitch Coaxial Dual-Rotor UAV

摘要: 为探明定桨距共轴双旋翼无人机悬停时上下桨盘间的气动干扰机理，针对一款小型共轴无人机建立气动数值模型。运用计算流体动力学(CFD)方法，对比分析了单旋翼基准、实机间距及不同间距比工况下的速度场、压力分布与载荷特性。结果表明：上旋翼下洗流会恶化下旋翼入流条件，导致下旋翼拉力较上旋翼减小约14% (上旋翼拉力约占总拉力的54%)，系统总拉力较两副孤立单旋翼损失约20%；以“总拉力不低于测试最大值的90%、净扭矩不高于0.1 N·m、流场未出现明显无序小尺度涡，并在满足上述条件时取最小轴向间距”为工程判据，推荐间距比范围为0.369~0.45；对于强调结构紧凑性的样机，选取该范围下限0.369；桨盘干扰会打破反扭矩平衡，使上旋翼扭矩较下旋翼小约6%，系统呈现逆时针自旋趋势。该研究结果可为共轴双旋翼无人机的结构布局优化、旋翼间距选取及差速偏航控制补偿提供理论依据。

Abstract: To investigate the aerodynamic interference mechanism between the upper and lower rotor disks of a fixed-pitch coaxial counter-rotating unmanned aerial vehicle (UAV) in hovering state, an aerodynamic numerical model was established for a small-scale coaxial UAV. Using computational fluid dynamics (CFD) methods, the velocity fields, pressure distributions, and load characteristics were comparatively analyzed under the baseline single-rotor condition, practical-clearance coaxial condition, and various rotor spacing ratio conditions. The results indicate that the downwash of the upper rotor deteriorates the inflow conditions of the lower rotor, leading to a 14% reduction in the thrust of the lower rotor compared to the upper rotor (with the upper rotor accounting for approximately 54% of the total thrust); moreover, the total thrust of the coaxial system suffers an approximate 20% loss compared to two isolated single rotors. Under an engineering criterion that (i) requires the total thrust to reach at least 90% of the maximum tested value, the net torque not to exceed 0.1 N·m, and no evident disordered small-scale vortices, and (ii) selects the minimum axial spacing satisfying these requirements, the recommended spacing-ratio range is 0.369~0.45. For the compact prototype equipped with 613-mm-diameter rotors, the lower bound (0.369) is selected. Furthermore, the inter-disk interference disrupts the anti-torque balance, rendering the torque of the upper rotor about 6% smaller than that of the lower rotor, which induces a counter-clockwise yawing trend in the system. The research findings provide a theoretical basis for the aerodynamic layout optimization, rotor spacing selection, and differential-torque yaw control compensation of coaxial UAVs.