A preliminary study of open rotor design using a harmonic balance method

Abstract

The open rotor system is considered as a next generation technology for an eco-friendly aero-engine system. Theoretically, the open rotor system can get unlimited high bypass ratio, which is more efficient than conventional turbofan engine system. However, a high acoustic noise loudness resulting from an absence of duct around the fan has been a major drawback of the open rotor system for its implementation in commercial aircrafts. In this preliminary design study, Harmonic balance method (HBM) was carried out to predict complex flow fields created by two coaxial, counter rotating rotors more efficient than the conventional time-accurate CFD method used in open rotor flows. The accuracy of the HBM was validated by wind-tunnel experiment of the scaled model of the open rotor. A noise prediction was computed using Ffowcs-Williams Hawking acoustic analogy. Genetic algorithm handling multi-objective and multidiscipline performed fitness evaluation, which were substituted into Kriging response surface approximation model to reduce the time to find an optimum. Tradeoff study between aerodynamic and aeroacoustic properties was plotted via pareto front. The optimum configuration obtained from the pareto front showed a reduction of noise level by 7dB and power level by 4% from the baseline values.