From design to flight testing : overview of rotorcraft acoustic research at Onera for industrial applications

The reduction of noise emission has become a key commercial argument for helicopter manufacturers, such as Airbus Helicopters. For years, Airbus helicopters has placed emphasis on the good acoustic behavior of its helicopters, as proven by its communication on the fenestron concept, the acceptance of its aircraft for the Grand Canyon tours and the presentation of its recent Bluecopter™ Technology. Thus, Airbus helicopters has become one of leaders in the manufacture of low noise helicopters. Some of its advances in this field have been made thanks to its cooperation with Onera. The paper is aimed at presenting the way in which Onera has become a reliable partner for industry to face the challenge. Partly thanks to wind tunnel tests, Onera has developed a set of numerical tools and acquired a physical understanding of the noise emitted by the rotors of helicopters. These tools have been used to design new main rotor blades, optimized to reduce the vibration, to improve the aerodynamic  performances and to reduce the noise emission for specific flight conditions. Both active devices and passive design have been developed and tested at model scale, before being provided to the industry for scale one developments and for implementation on actual helicopters and to be tested in flight. For the tail rotor, fenestron noise has also been studied numerically and during flight tests, in order to determine noisy flight  conditions and to improve the tools and methodology for future definition and optimization.