Numerical Evaluation of Microflaps for On Blade Control of Noise and Vibration

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 is modeled using a nonlinear CFD based reduced order aerodynamic model that takes into account unsteadiness, compressibility and time varying freestream effects. Active control studies employing microflaps are conducted on a hingeless rotor configuration resembling the MBB BO-105, and various spanwise configurations of the microflaps, including a single, a dual, and a segmented five-microflap configuration are evaluated. Results indicate that the microflap is capable of substantial reductions in blade vortex interaction (BVI) noise ranging from 3-6 dB. Vibration reduction ranging from 70-90% is also demonstrated. The interaction of vibration and noise reduction is also examined, and it was found reduction in one objective is accompanied by an increase in the other, a trend also observed when using other active 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 may also have potential for rotor performance enhancement.