Acoustic Analysis of Counter-Rotating Open Rotors with a Locked Blade Row

Abstract

Counter-rotating open rotors (CRORs) have the potential to reduce environmental emissions thanks to their high propulsive efficiency. However, there are a number of concerns surrounding their acoustic emissions. This contribution presents a novel multiconfiguration CROR that offers considerable noise reductions. In particular, locking either the fore or aft rotor during takeoff is considered, with the running rotor providing the required thrust. During cruise, both rotors are operated to retain the high efficiency of the CROR. A coupled computational fluid dynamics/computational aeroacoustics analysis has shown the potential of this multiconfiguration concept to offer substantial noise reductions when compared to a baseline CROR. During a simulated constant-altitude flyover at takeoff conditions, reductions of 3.5 and 7.9 dBA have been demonstrated when either the fore or aft row is locked, respectively. Using the effective perceived noise level metric, this result corresponded to 7 and 12 Effective Perceived Noise Level (in Decibels), respectively, for the same flyover.