Study of the attenuation of sound propagating through rotor cascade and a variable area duct

Rotor-stator interaction, a clear and powerful noise source, usually takes place on stator with the upstream rotor-wake impacting. Consequently, the interaction noise must propagate through the rotor to radiate from the engine nacelle. This propagation attenuates the acoustic emissions, and should be considered when calculating interaction noise. The transfer element method is applied in the present paper to analyse the influence of rotor on the transmission of the interaction noise. The influence of a nacelle with variable area duct and intake cone is also considered. The method will be illustrated by means of numerical examples. It appears that, the influence of duct shape on sound propagation cannot be ignored if accurate calculations are performed. Depending on the reasonable choice of stator number, the shielding effect of rotor can generate a positive reduction in acoustic power. In addition, the chord width is an important parameter to optimize the acoustic shielding of the rotor.