Control of Reverse Flow using Trailing Edge Morphing

At high speeds, a portion of the retreating blade of a rotorcraft can enter a regime of reverse flow. The reverse flow starts to separate at very low angles of attack, leading to an increase in drag, production of negative lift, and a pitching moment impulse. In addition, periodic formation and shedding of the separation bubble during dynamic pitching leads to a large increase in hysteresis. The proposed method for mitigating these negative effects is a trailing edge reflex camber over the final quarter chord of the blade. Experiments were performed on a 20° forward swept blade and 20° backward swept blade with and without trailing edge morphing. Load cell measurements were taken at a chord-based Reynolds number of 2.38 × 10⁵ across a wide range of angles of attack. Stereoscopic Particle Image Velocimetry (SPIV) was also performed at the same Reynolds number at a single angle of attack. The load cell measurements showed a decrease in adverse effects when using the cambered geometry for both sweep angles. The SPIV results showed a significant reduction in the size of the separation bubble over the cambered blade, which was the cause of the reduction in the adverse effects.