Fan noise reduction including the effects of swept-and-leaned vanes and acoustic treatment

A swept and leaned stator is an effective means of the passive control of fan interaction noise. Based on the three-dimensional analysis, it's found that the selection of vanes sweep and lean may change the modal pressure distributions of the sound. And the sound propagation in the duct also affects the aerodynamic response on the vanes, which is regarded as the main sound source of fan interaction noise. Meanwhile, the acoustic liners optimization is aimed at the greatest attenuation of sound in an engine nacelle. In this process, the noise source models are usually assumed to be one single mode or multi propagating modes with equal energy. In this paper, the transfer element method is employed in order to include the stator and the acoustic treatment at the same time. The transfer element for a stator is established based on the three-dimensional lifting surface method. The effect of a duct liner is modelled by monopole sources. All the elements are finite length and coupled at the interface planes by solving a linear system. The results show that the optimal range of the liner's impedance may be greatly changed when including the effect of vanes sweep and lean. Further reduction of fan interaction noise is ex-pected for the system acoustic design in the nacelle.