Theoretical studies of the active control of propeller-induced cabin noise

Abstract

A simple analytical theory is used to model the fuselage structural response of a B.Ae. 748 aircraft as a finite, isotropic thin cylindrical shell, and the cabin acoustic response as a cylindrical room. Theoretical results are compared with measured flight data obtained on a test aircraft. It is shown that, provided that the theoretical external acoustic pressure forcing of the shell is representative of the measured propeller pressure field acting on the aircraft fuselage, then the simple model can yield structural and acoustic responses which show good agreement with the measured data. This model is used to predict the effectiveness of a 16 source/32 error sensor active noise control system when applied to the predicted cabin sound fields at the first (88 Hz) and second harmonic propeller blade passage frequencies. An attempt is made to reduce the average sound level over a head height plane covering all 48 passenger seats. Average reductions over the plane of the order of 14 dB for the fundamental frequency and 4 dB for the second harmonic frequency are predicted. These results involve local reductions of up to 35 dB, but the spatial extent of these high-level reductions is shown to be considerably smaller for the second harmonic frequency than the fundamental frequency.