A Computational Study of Microflaps with Application to Vibration Reduction in Helicopter Rotors

Abstract

of oscillating Gurney flaps, or microflaps, has been conducted. Two-dimensional unsteady airloads, lift, moment and drag, due to an oscillating microflap were computed using a compressible Reynolds-Averaged Navier-Stokes (RANS) flow solver. The CFD results were generated with an overset mesh approach that captures oscillatory microflap motion. Three microflap configurations were examined so as to determine the type most suitable in terms of actuation eciency and practical implementation. Furthermore, a reduced order model (ROM) for the unsteady microflaps was developed based on CFD simulations, using the Rational Function Approximation (RFA) approach. The resulting RFA model is a state-space, time-domain aerodynamic model that accounts for unsteadiness, compressibility and time-varying freestream eect, suitable for use with comprehensive rotorcraft simulations. The agreement between the ROM and direct CFD calculations was found to be excellent even in presence of strong nonlinear flow eects. The approximate model is suitable for incorporation in a comprehensive code, from which the potential of microflaps for active control of vibrations in rotor can be determined. Preliminary studies with open loop control showed that the microflap produces substantial vibration reduction (52% reduction in vertical shear) on a hingeless rotor configuration resembling the MBB BO-105, confirming the control authority of this novel technique.