Comprehensive Numerical Assessment of Rotorcraft Vibration and Noise Control Using Microflaps

Abstract

Active Gurney flaps, or microflaps, are studied to determine their effectiveness in reducing noise and vibration in rotorcraft as well as improving rotor performance. The effectiveness of the microflap is examined using a comprehensive rotorcraft simulation code. The aerodynamic properties of the microflap are modeled using a nonlinear computational-fluid-dynamics-based reduced-order aerodynamic model that takes into account unsteadiness, compressibility, and time-varying freestream effects. Active control studies are conducted on a hingeless rotor configuration resembling the Messerschmitt-Bölkow-Blohm BO-105, using various spanwise microflap configurations, including single, dual, and segmented five-microflap configurations. Results indicate that the microflap is capable of substantial reductions in blade–vortex interaction noise ranging from 3 to 6 dB. Vibration reduction ranging from 70 to 90% is also demonstrated. The effect of vibration reduction on noise and vice versa is also examined, and it was found that reduction in one objective is accompanied by an increase in the other, a trend also observed when using other active control approaches. Finally, the microflap is considered for combined vibration reduction and performance enhancement at a high-speed cruise flight condition. The results clearly indicate that the microflaps are very effective for both noise and vibration reduction in helicopters, and they also have potential for rotor performance enhancement.