Aeroacoustic research and noise reduction for aircraft - mechanisms, technologies, perspectives -

Abstract

Exterior noise of air vehicles of any kind originates from aerodynamic sources of sound. These in turn occur at functional components for aerodynamics (propellers, open rotors, fans, jets, flaps, slats, undercarriages) which as such are indispensable for the primary purpose of the aircraft: making it fly. By definition they manipulate the airflow and thus, they operate more or less openly in the acoustic medium which directly transmits the sound: there is no (aerodynamic) design space to encapsulate the sources, neither any technology which would increase mass. Although special flight procedures may reduce some of the impacting noise at the receiver, their effect is limited and sometimes impossible to implement. In consequence, and most effective, is the noise reduction at the source. In this sense the technical task goes beyond issues occurring on aircraft, but extends to a vast set of technical products in general. There are two possible paths to source noise reduction: a) design of aerodynamic shapes, and b) use of special materials. In order to do so, engineers need aeroacoustic knowledge and respective prediction methods. Moreover, although nowadays it is possible to generate humongous amounts of data techniques are needed to turn data into useful information and knowledge. The keynote lecture discusses various source noise reduction technologies from a fundamental stage up to their implementation and test on aircraft as demonstrated in flight tests at DLR. Finally, the transfer of ideas to the automotive and ventilation sector is discussed and an outlook to future developments is given.