In turboprop aircraft tonal interior noise with high sound pressure levels occurs at low frequencies (f < 500 Hz). The excitation frequencies are given by the blade passage frequency (BPF) and its higher harmonics. The high tonal noise levels at these tones result from the propellers, which are mainly optimized in terms of performance. The acoustic properties are usually not taken into account. In order to obtain an acceptable interior noise level inside the aircraft, passive methods are commonly used, e.g. adding material for the purpose of noise transmission loss or absorption. Especially for the reduction of low frequency propeller noise, this results in a tremendous amount of unwanted weight. In order to avoid this extra weight, in many of the existing turboprop aircraft passively acting dynamic vibration absorbers, which are tuned to the critical propeller tones are installed. Their purpose is to avoid the primary structure of radiating propeller tone excited noise into the aircraft interior. However this treatment is not sufficient for those turboprop aircraft that have powerful high performance engines, which consequently induce high noise levels into the aircraft interior for which passive solutions end up with high weight. A solution is to apply active noise control systems (ANC), which focus on the unwanted tonal noise at low frequencies and provide a good compromise of noise reduction performance and the amount of additional weight. This paper briefly describes different ANC applications currently under development for a high-speed turboprop transport aircraft, which is the Airbus A400M.
Active acoustic solutions for a high speed turboprop transport aircraft
Aktive akustische Lösungen für ein Hochgeschwindigkeits-Transportflugzeug mit Propellerturbinentriebwerk
2009
12 Seiten, 13 Bilder, 1 Tabelle, 5 Quellen
Conference paper
English