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 (1.) challenging low interior noise targets like Saab 2000 or Bombardier Dash 8 Q 400 or (2.) 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 for latter mentioned cases is to apply an active noise control systems (ANC), which focuses on the unwanted tonal noise at low frequencies and provides a good compromise of noise reduction performance and the amount of additional weight. This paper briefly describes two different ANC applications currently under development for a high-speed turboprop transport aircraft, which is the Airbus A400M.
Development of active noise reduction systems for a high speed turboprop transport aircraft
Adaptronic Congress, 13 ; 23-29
2009
7 Seiten, 12 Bilder
Conference paper
English
Active acoustic solutions for a high speed turboprop transport aircraft
Tema Archive | 2009
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