In high-speed rotorcraft applications, large sections of a blade undergo reverse flow due to a high advance ratio. Flow separation at the sharp aerodynamic leading edge during reverse flow leads to negative lift, pitching moment, and drag penalties. The kinematics of a rotor blade leads to a dynamic stall in reverse flow, which further accentuates the problem by causing unsteady loading. The present experimental study shows that these problems can be mitigated by passively morphing the camber near the trailing edge of the blade. A finite-span cantilevered NACA 63-218 blade was examined at a chord-based Reynolds number of $3.75\times {10}^5$ with and without trailing-edge morphing. The morphing was implemented by deflecting the last quarter-chord near the trailing edge by 5, 10, or 15 deg. Experiments included global measurements of the forces and moments using a load cell as well as detailed flow measurements using stereoscopic particle image velocimetry. A couple of scenarios were explored: static pitch and dynamic pitch at different pitch amplitudes and frequencies. Cambering of the blade near its trailing edge led to a significant reduction in the size of the separation region over the model, and of the wake. For the static pitch case, it led to a large reduction in drag and pitching moment and a minor reduction in negative lift. For the dynamic pitch cases, the hysteresis loop was significantly reduced, leading to a large reduction in unsteady loading.

在高速旋翼机应用中，由于高提前比，叶片的大部分会经历反向流动。反向流动期间锐利的空气动力学前缘处的流动分离导致负升力、俯仰力矩和阻力损失。转子叶片的运动学会导致反向流动中的动态失速，这会导致不稳定的负载，从而进一步加剧问题。目前的实验研究表明，这些问题可以通过被动地改变叶片后缘附近的弧度来缓解。有限跨度悬臂 NACA 63-218 叶片在基于弦的雷诺数为$3.75\times {10}^5$有和没有后缘变形。变形是通过将后缘附近的最后一个四分之一弦偏转 5、10 或 15 度来实现的。实验包括使用称重传感器的力和力矩的全局测量以及使用立体粒子图像测速法的详细流量测量。探索了几个场景：不同音高幅度和频率下的静态音高和动态音高。叶片在其后缘附近的弯曲导致模型上分离区域和尾流的尺寸显着减小。对于静态俯仰情况，它导致阻力和俯仰力矩大幅减少，负升力略有减少。对于动态俯仰情况，滞后回线显着减少，导致非定常载荷大幅减少。