Mutual effect between swept-and-leaned vanes and acoustic liners on fan interaction-noise reduction

The swept-and-leaned vanes and acoustic liners can both be used to reduce the turbofan noise. In this work, an analytical model was proposed under an idealized condition, in which an annular stator cascade and a locally reacting liner exist in an infinite duct at the same time, to study the mutual effect between these two techniques. Based on the transfer element method, the system matrix of multi-elements can be established based on the continuity of disturbance pressure and velocity at the interfaces. The acoustic elements for a stator and a liner were established, respectively, by employing the three-dimensional lifting-surface method and the equivalent surface source method, which are both the so-called methods of singularity. The interface matching pattern between adjacent elements was improved in this paper with more physics included, which can also be combined with the numerical methods easier. Because the technologies for fan-noise reduction, which are the swept-and-leaned vanes and acoustic liners in this paper, are both closely related to the modal acoustic field in the duct, the coupling effect can be strong in some conditions. The results showed that the noise reduction gained by these two techniques cannot be superposed simply. They should not be considered isolatedly. Further discussions on the transmission and reflection between different kinds of acoustic elements should be made to achieve the system optimization in the nacelle.