Passive Noise Control oriented design of aircraft headrests

Propeller blades and Turbulent Boundary Layer (TBL) represent the main noise contributors of a turboprop aircraft, causing both passenger discomfort and community annoyance. In this work, two technologies for Passive Noise Control (PNC) are numerically evaluated in terms of Sound Pressure Level (SPL) computed at passengers' ears. A technology is based on the shape optimization of the headrests for reducing the SPLs perceived by passengers, whereas a second technology is based on the adoption of nanofiber textiles to improve the absorbing performances of the headrests, in turn reducing the corresponding SPLs. To this aim, a numerical SEA model of a turboprop aircraft fuselage has been used to predict the internal noise in the frequency range 200 - 4000 Hz. The TBL aeroacoustic load has been considered as the unique noise contributor in such frequency range. Then, the average SPL of the cavities inside the aircraft cabin has been carried out and then considered as input load around a single seat modelled with the Boundary Element Method (BEM). Finally, the latter BEM model has been used to evaluate different configurations of headrest shapes and headrest covering textiles in terms of their acoustic performances. The work shows how an acoustic-oriented design of the aircraft headrests allows an average SPL reduction for passengers up to 3 dBA.