Noise Reduction on a Model Helicopter Rotor Using Dielectric Barrier Discharge Plasma Actuators

Abstract

Noise reduction was studied on a model helicopter rotor using pulsed dielectric barrier discharge (DBD) plasma actuators mounted at the blades’ leading edges. The evaluation was performed in a fully anechoic chamber, where thrust and torque were measured concurrently with the acoustic signature using an array of 15 microphones. Acoustic measurements were made for both baseline and actuated cases at a fixed collective pitch angle under conditions of constant thrust. Actuation produced broadband and tonal noise reductions of up to 8 and 3 dB, respectively, while simultaneously increasing the rotor figure of merit by 25%. Broadband noise reductions were due to control of the otherwise separated boundary layer, resulting in smaller and weaker turbulent eddies in the wake and the tip-vortex and, therefore, smaller turbulent surface pressure fluctuations. Noise reduction directivity associated with the blade passing frequency of up to 3 dB was consistent with rotational noise theory. At most of the observer angles, both the plasma pulsation and ionization frequencies were not visible in the spectra above the motor self-noise signature. Peaks in the second harmonic were observed at specific observer angles and were assumed to be due to the geometric mounting of the actuator and amplification of the pulsations in the laminar separation bubble.