垂直下降状态下螺旋桨气动特性及涡环特征

Aerodynamic characteristics and vortex ring features of propeller in vertical descent

  • 摘要: 螺旋桨在垂直下降状态下极易进入涡环状态(vortex ring state, VRS),从而引起复杂的空气动力学特性。采用黏性涡粒子方法(viscous vortex particle method, VVPM),对APC thin electric 10X7 螺旋桨在不同垂直下降率下的气动特性和涡环特征开展研究。结果表明:螺旋桨气动特性容易受到下降率的影响,当下降率增加时,拉力呈现先略增大再减小后增大的趋势,同时尾迹压缩效应逐渐增强,涡环中心逐渐上移。在此过程中,涡环先后经历了悬停状态、涡环前期、涡环初期、深度涡环和类风车流动状态,涡环特征从管状螺旋下洗涡逐渐演变成螺旋涡与环形涡并存,再到完全涡环结构,最后涡系结构移动至桨盘上方。涡场拓扑结构的演变直接影响螺旋桨的气动特性,当桨盘附近尾迹为管状螺旋涡结构时,螺旋桨气动特性变化不明显;随着下降率的增加,逐渐演变出的环形涡会严重影响螺旋桨的气动特性,表现为拉力骤降,尾迹压缩效应增强,回流区包裹桨盘;随着下降率进一步增加,涡系结构到达桨盘上方,螺旋桨进入类风车状态,气动力逐渐增大。

     

    Abstract: Propellers are susceptible to entering the perilous Vortex Ring State (VRS) during vertical descent, a phenomenon that results in complex aerodynamic characteristics that remain incompletely understood. Utilizing the Viscous Vortex Particle Method (VVPM), a thorough investigation is conducted on the aerodynamic characteristics and vortex ring features of the APC thin electric 10X7 propeller at different vertical descent rates. Results show that the propeller's aerodynamic characteristics are highly susceptible to the change in the descent rate. Specifically, as the vertical descent rate increases, the thrust initially experiences a slight increase, followed by a decrease, and ultimately a subsequent increase. Concurrently, the wake compression effect becomes progressively more pronounced, and the vortex ring center gradually shifts upwards. During this process, the vortex ring state initially hovers, evolves gradually to the fully developed state, and ultimately transforms into a windmill-like flow state. The wake fields of the propeller gradually change from tubular helicoidal downwash vortical structures to the coexistence of tubular and toroidal vortical structures, and then to the fully-toroidal ones, which finally move completely to the top of the propeller disk. Such a topological evolution of the vortex field has a direct impact on the propeller's aerodynamic characteristics. Tubular helicoidal vortical structures exert negligible influence, while toroidal vortical structures have a significant impact as the descent rate increases, evident in a sudden thrust decrease, the enhancement of the wake compression effect, the encirclement of propeller discs by backflows, and the increased aerodynamic force.

     

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