Abstract:Nowadays all the large civil aircrafts use acoustic liner to meet the strict noise regulations. The existing aero-engine noise reduction work mainly focus on the liner optimization design to deal with the forward fan noise, and they are mainly a two-dimensional axisymmetric noise reduction designs. Compared to forward fan noise, the accurate prediction of aft fan noise is a challenge. In this paper, based on the parabola approximation technique and Kriging surrogate model, the three-dimensional bypass liner design method and procedure for aft fan propagation noise are proposed. Firstly, the parabolic approximation equation is derived based on the linearized Euler equation. The coupling problem of two-way sound propagation in turbofan is approximated to one-way sound propagation in bypass duct. Secondly, the parabolic equation is solved numerically to obtain the prediction results of aft fan propagation noise, in which the spatial discretization is carried out by using the high-order dispersion relation preserving (DRP) scheme and time marching is performed by low dispersion Runge Kutta (LDDRK) scheme. And the efficiency of three-dimensional sound propagation calculation is improved significantly. Meanwhile, a surrogate model is established to reduce the overall optimization cost, and a three-dimensional bypass liner design method for aft fan propagation noise is developed, which takes into account the accuracy and calculation efficiency. The results show that the developed method can efficiently design the three-dimensional acoustic liner to reduce the aft fan noise on the premise of meeting the calculation accuracy.