Control of Reverse Flow over a Periodically Pitching Blade using Camber Morphing

Due to the complicated dynamics associated with rotorcraft flight, portions of the rotor disk experience reverse flow where flow travels from the sharp trailing edge of the rotor blade to the blunt leading edge of the blade. This results in several negative effects. In this work, a series of wind tunnel experiments were conducted on swept blades undergoing a sinusoidal pitching motion to investigate the effect of trailing edge reflex camber on reverse flow aerodynamics of a pitching blade. Cycle-averaged load measurements showed that the introduction of trailing-edge reflex camber led to a reduction in the cycle hysteresis regardless of blade sweep angle. Phase-averages SPIV measurements at select spanwise location showed the introduction of trailing-edge camber reduced the size of the separation bubble at a given angle of attack relative to the baseline case. In addition, the flow fields at the same angle of attack during the pitch up and pitch down motions were found to be more similar for the camber morphed blades compared to the corresponding unmorphed blades, providing the explanation for the reduced hysteresis in the aerodynamic loads seen for the cambered models during the dynamic pitch motion.