Vibration Reduction on Helicopter Rotors Using Open-Loop Flow Control

The effectiveness of active flow control for reducing vibrations in helicopter rotors is examined using numerical simulations. The flow control actuators employ pulsed fluidic jets on the pressure side (PS) and suction side (SS) of the airfoil and are installed near the trailing edge of the blades. The flow control region extends over 12% of the blade span and is centered at the 75% span location. A reduced-order model (ROM) of the unsteady aerodynamic effects introduced by the actuators is developed. The ROM is trained using data obtained from unsteady Reynolds-averaged Navier-Stokes simulations performed across a broad range of flow conditions representing the rotor environment. The ROM is incorporated in a comprehensive aeroelastic rotor simulation code. Open-loop control, consisting of alternating PS and SS actuation at various frequencies, is applied on a four-blade hingeless rotor resembling the Messerschmitt-Bolkow-Blohm Bo-105 rotor in level flight with an advance ratio of 0.30. The results indicate that the flow control actuators have significant control authority to modify the vibratory loads, with up to 85% reduction in the four-per-revolution vertical shear force at the rotor hub. The tradeoff between vibratory load reduction and rotor performance is also examined. A 5.3% increase in rotor power accompanies the vibratory load reduction.