Efficient design optimization of flexible CROR blade for low-level noise

Abstract

An efficient and accurate analysis method to solve fluid and structure interaction (FSI) problems under time-dependent motions is studied. A time-domain harmonic balance method (HBM) approaches are known to be more efficient and accurate enough for the periodic problem of the conter-rotating open rotor (CROR) system. Through a Fourier-series assumption of flow/structural variables, a time-derivative term is replaced with a harmonic source term which can be treated with additional source term. As a result, the unsteady analysis reduces to the steady analysis. In perspective of coupling fluid and structure analysis, the HBM can be applied to structural analysis as like in the aerodynamic analysis. Unlike the traditional time-accurate analysis method to exchange airloads and deformations at every physical time, those information are transferred at few number of time instances during the pseudo-time iterations of HBM. A loudness of open rotor is primary obstacle to be utilized in industry field, even with the outstanding propulsive performance. Along with the HBM-based aeroelastic analysis, an aeroacoustics analysis is carried out using the Ffowcs-Williams Hawkings equations on the permeable integral surface. As the best use of the efficient HBM-based aeroelastics/aeroacoustics analysis, the multidisciplinary design optimization is performed to reduce the noise level of open rotor system, while the aerodynamic performance is retained with the desired level.