Acoustic Resonance in Aeroengine Intake Ducts

A theoretical model is used to investigate the effect of geometry, flow conditions and acoustic lining on the occurrence of acoustic resonance within aeroengine ducts. Semi-analytical methods are used to demonstrate that two types of acoustic resonance can be excited. The first is an intake resonance arising due to axial variation of the intake shape and the presence of swirling flow downstream of the rotor. The second occurs as a result of mode trapping between the rotor and stator. Such resonance phenomena may be relevant to the destabilization of the fan and the onset of flutter and rotating stall.