Aircraft cabin noise reduction by means of acoustic black holes

Regarding the aims of Flightpath 2050, aircraft noise in general must be reduced drastically during the next three decades. An acceptable or even comfortable cabin noise is one aspect of this challenge and a crucial factor for the introduction of new technologies in aircraft. One promising possibility is the use of highly innovative damping technologies in combination with drastic design changes. During the past decades, acoustic black holes have been introduced as highly efficient vibration damping systems. The vibration amplitudes, the radiation coefficient and the weight of plate structures can be reduced in parallel. Both, the acoustic performance gain and the weight reduction are excellent characteristics for passive vibration damping of aircraft structures. Acoustic black holes have mainly been investigated in simple structures to clarify a lot of basic research questions concerning positioning, shaping and damping application. This contribution illustrates the possibility of introducing acoustic black holes into the inner cabin linings of a research aircraft developed within the Coordinated Research Centre 88o. A generic mechanical model of the aircraft is used to predict the cabin noise. The model includes the primary and secondary structure, the insulation and the passenger cavity. It is numerically solved using the Finite Element Method (FEM). In a second calculation, acoustic black holes are considered in the cabin linings. The results show a comparison of the transmission loss with and without acoustic black holes. The potential reduction of cabin noise due to acoustic black holes in cabin linings is assessed.