Open Rotor Blade Leading Edge Optimization to Mitigate Noise Increase Due to Flow Incidence

Abstract

The ductless feature of the open rotor allows design of a higher bypass ratio engine that can lead to an increase in engine propulsive efficiency. However, the open rotor may experience a change of inflow conditions during takeoff and approach operation to the blade due to the installation features such as a wing and/or the angle-of-attack effect that produces the upwash. The angled inflow can induce partial flow separation along the open rotor blade with resulting impact on noise. This paper focuses on a new open rotor blade design feature to reduce the impact of flow incidence on noise. A novel feature proposed here is partial drooping of the blade leading edge. A numerical optimization method is used to find the design that best mitigates the impact of flow incidence on noise. The results proved that the partial leading edge drooping could reduce the wake and tip vortices significantly at high incidence condition by preventing the migration of the separated flow toward the blade tip.