极低雷诺数下超微型旋翼桨叶仿生运动流动控制机理研究

The research on the flight mechanism of Nano Air Vehicle (NAV) showed that the propulsive performance of nano rotor degradated dramatically due to the reduction of the flight Reynolds number. So how to improve the propulsive performance of nano rotor turns out to be a difficulty for NAV design. In our previous study, it was found that the bio-inspired motion of blade airfoil along the longitudinal axis of blade affected the flow field around the airfoil at ultra-low Reynolds number, as a result of which the aerodynamic performance of airfoil was enhanced. Therefore, a method is proposed to improve the performance of nano rotor by controlling the flow around the blade by virtue of the bio-inspired blade motion along the longitudinal axis. The research will be carried out with theoretical and experimental methods to find out the flow control mechanism. Firstly, the law of effect of bio-inspired blade motion parameters on the propulsive performance of nano rotor is to be studied experimentally at ultra-low Reynolds number. And the feasibility of improving the propulsive performance of nano rotor with the bio-inspired blade motion will be verified. In addition, Particle Image Velocimetry (PIV) method is to be used to measure the velocity and vorticity contour around the rotor blade sections with bio-inspired blade motion. These results together with numerical results will be utilised to analyze the unsteady flow mechanisms induced by the coupling of the nano rotor rotation and bio-inspired blade motion. The mechanism of the effect of flow control on the propulsive performance of nano rotor will be found so as to redound to the design of rotary-wing nano air vehicle.

对超微型飞行器飞行机理的研究表明，超微型旋翼推进性能随着雷诺数的减小而急剧下降，如何改善旋翼的推进性能是超微型飞行器设计的一个难题。我们对极低雷诺数下二维桨叶翼型的研究发现，对该翼型采用绕桨轴的仿生运动控制，会使翼型周围的流动发生变化，提升翼型的气动特性。据此，本项目拟借助于桨叶沿桨轴的仿生运动，达到对极低雷诺数下超微型旋翼桨叶周围流动控制的目的，以提高旋翼的推进特性。通过理论分析、实验测试及二者的结合，揭示流动控制的机理：首先采用实验测量方法研究极低雷诺数下超微型旋翼桨叶仿生运动参数对旋翼推进特性的影响规律，证实仿生运动流动控制对提高旋翼性能的有效性；同时，采用粒子成像测速方法实验测量旋翼桨叶截面处流体的速度、涡量云图；再结合数值仿真方法分析桨叶旋转运动和仿生运动耦合下引起的非稳态流动机制，揭示流动控制对超微型旋翼推进性能影响的机理，从而为超微型旋翼飞行器设计提供支撑。

对超微型飞行器飞行机理的研究表明，超微型旋翼推进性能随着雷诺数的减小而急剧下降，如何改善旋翼的推进性能是超微型飞行器设计的一个难题。本课题提出了利用桨叶沿着桨轴的仿生运动，达到对极低雷诺数下超微型旋翼桨叶周围流动控制以提升推进特性的目的。本课题首先针对无仿生运动的超微型旋翼的悬停性能和流场开展了研究。建立了极低雷诺数下超微型旋翼求解器，搭建了超微型旋翼悬停实验平台，研究了旋翼几何参数和运动参数对悬停性能影响。结果发现，随雷诺数的降低，超微型旋翼的推进性能下降，性能系数在0.6以下。并随着旋翼转速的增加，超微型旋翼的推力系数和功率系数增大。对具有不同桨叶充实比和扭转角分布的旋翼研究表明，旋翼的扭转角影响功率系数，而充实比提升了推进系数。流场研究表明，前缘涡是影响旋翼性能的重要因素，由于旋翼边界层的分离造成了旋翼气动特性的下降。其次，开展了仿生运动超微型旋翼的悬停性能和流场研究。建立了超微型旋翼仿生流场研究的求解方法，搭建了仿生超微型旋翼悬停性能测量和实验测量平台。在旋转过程中引入俯仰运动，建立了旋翼俯仰运动的气动模型，分别开展了超微型仿生旋翼的推进性能研究和流场特性的研究。研究表明俯仰运动可以有效提升旋翼推进性能，且随频率的不同而不同。在频率为4次/转时，旋翼的推进性能提升最大，达到了7.2%，从流场分析可知旋翼仿生运动引起了非稳态的流场。在高斯特劳哈尔数，前缘涡的周期性脱落提升了旋翼特性，而在低斯特劳哈尔数，前缘涡和后缘涡的演化共同延迟了失速，是提升旋翼特性的重要原因。本课题的研究揭示了非稳态流动控制对超微型旋翼推进性能影响的机理，为小型旋翼推进性能的提升提供了新的手段，从而为超微型旋翼飞行器设计提供了支撑。