Feasibility of Arbitrary Pitching Motion Controlled by Piezoceramic Actuators to Reduce Blade-Vortex Interaction Noise.

Previous work utilizing piezoceramic actuators to dynamically modify the twist of rotor blades has concentrated on vibration reduction. This study investigates the feasibility of using the same approach for noise control by reducing the fluctuating loads caused by Blade-Vortex Interactions (BVI). A two-dimensional airfoil version of the TURNS (Transonic Unsteady Rotor Navier-Stokes) code is modified to model the interaction of a pitching airfoil with a vortex. The airfoil motion is prescribed using quasi-steady thin airfoil theory, and a knowledge of the time history of the blade loading during a previous vortex passage. The influence of the vortex on the loading of the airfoil is found to be alleviated considerably by pitching the airfoil. Also, the time rate of change of the loading, which influences the amplitude of the accompanying acoustic signature, is reduced by a factor of 2, after only one control loop. A strong transonic case indicates that such an approach remains effective even when supersonic pockets are present. An analytical study of the response of the blade with embedded piezoceramic actuators indicates that the frequencies of the twist required to perform this control are within the capacity of the state-of-the-art “smart rotors”. However, the amplitude is still somewhat limited. Despite this fact, the current technology has the potential to reduce the blade-vortex interaction noise by 3 dB. Continued improvements in actuator technology combined with additional analysis should result in a very promising BVI noise control system.