Psychoacoustic evaluation of noises produced by propellers with asymmetrical blade spacing
نویسندگان
چکیده
Instrumental evaluations (e.g. Dobrzynski, InterNoise 90) showed that propeller noise can be reduced by asymmetrical blade spacing. Compared to conventional propellers with 6 blades and symmetrical spacing of 60°, propellers with asymmetric spacing of 15° produce about 3 dB(A) less level, in particular for high helical blade tip Mach numbers HBTMN. Since the aerodynamic propeller performance is not affected by asymmetrical blade spacing, this technique might be regarded as an effective means for noise reduction of propelled aircraft. However, before drawing such a conclusion based solely on instrumental evaluations, subjective evaluations of sounds from asymmetrically spaced propellers are advisable. Therefore, loudness, sharpness, pitch strength, and annoyance of the propeller sounds were studied in psychoacoustic experiments. The results showed that propellers with symmetric vs. asymmetric blade spacing elicit almost the same loudness and annoyance when measured in lab studies. However, in particular at high HBTMN, propellers with asymmetric blade spacing produce less sharpness and pitch strength.
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