应用于风扇后传噪声的三维降噪声衬优化设计技术

当今大型民机无一例外均采用降噪声衬来满足噪声控制要求。已有的航空发动机降噪工作主要是针对风扇前传噪声进行声衬优化设计且为二维轴对称声衬降噪设计。与风扇前传噪声相比，风扇后传噪声的准确预测是个挑战。本文发展了基于抛物线近似技术和Kriging代理模型技术，提出了风扇后传噪声三维降噪声衬设计方法和流程。首先基于线化欧拉方程，推导了其抛物线近似方程，把双向声传播的耦合问题近似成单向声传播问题，其次采用高阶色散关系保持(DRP)空间离散和低耗散、低色散龙格库塔方法（LDDRK）时间推进格式数值求解抛物线方程得到风扇后传噪声声传播预测结果，显著提高了三维声传播计算效率。同时建立代理模型降低优化寻优开销，发展了兼顾精度和计算效率的风扇后传噪声三维降噪声衬快速设计方法。验证算例表明，本文发展方法可以在满足计算精度前提下，高效率设计可降低风扇后传噪声的三维声衬。

Research on the Three-dimensional Bypass Liner Design Method for Aft Fan Noise

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.