Noise reduction arrangement for the air inlet of an aircraft turbo-fan engine

摘要

A combination of blowing slots 4, 5 and acoustic lining segments 6, 7, 8 is provided on the interior surface 3 of an engine air inlet cowling or nacelle. A front blowing slot 4 in the shape of an annular downstream-facing step is followed immediately by two acoustic lining segments 6, 7 which are followed in turn by a further slot/lining combination 5, 8. Air from the blowing slots 4, 5 flows tangentially in a boundary layer over the acoustic lining surfaces 6, 7, 8 at higher speeds than that of the inlet mean flow, enhancing the noise attenuation performance of the acoustic linings above that of the acoustic linings alone. The slot-lining combination can be repeated multiple times in series along the inlet interior surface. The acoustic linings 6, 7, 8 may be optimized for different frequencies, eg below, near and above blade passing frequency (BPF).