气动噪声的准确数值模拟对于研究航空发动机中叶片绕流噪声和涡声共振现象具有重要的意义。提出了一种基于局部边界加密的改进虚拟单元浸没边界法，将其与高精度有限差分算法相结合，成功实现了对低雷诺数气动声场问题的直接数值求解。该浸没边界法的改进之处在于通过在虚拟点之间构造多个中间节点，并依据边界条件建立流体域内镜像点与固体域内中间点之间的关系，使得固壁边界的离散程度相比原来大为增加，这样起到对固壁边界局部加密的作用，从而使得边界的描述更为准确。通过对低雷诺数下圆柱绕流气动噪声问题的数值验证，表明所提出方法得到的升阻力特性、尾迹脱落涡演化以及近远场噪声传播特性与文献结果吻合较好，气动声场的计算精度得到了提高。对比研究了不同纵横比对椭圆绕流气动声源产生和噪声传播规律的影响，发现尾迹脱落涡交替排列并向下游演化，所形成的噪声场关于长轴线呈对称分布，其流动模式和声场特征与圆柱绕流类似，但其升阻力脉动以及噪声强度明显小于圆柱算例。进一步地，通过声压分解发现偶极子声源对整体噪声强度的贡献比重随着纵横比减小而下降，进而尾迹中单极子和四极子声源的贡献比重上升，直接导致了噪声传播方向向上游偏转。

Accurate numerical simulation of aerodynamic noise is of great significance for the study on flow-induced noise and vortex-acoustic resonance of aeroengine blades. This paper proposes an improved ghost-cell immersed boundary method based on local boundary refinement， which is combined with the high-precision finite difference method to successfully solve the fluid-solid coupling aeroacoustic problem at a low Reynolds number. The improvement in the current immersed boundary method includes the construction of a large number of intermediate nodes between the ghost points， and the establishment of relationship between the mirror image points in the fluid domain and the intermediate points in the solid domain according to the boundary conditions. Compared with the previous method， the dispersion of the solid wall boundary is significantly increased， thereby playing a role in local mesh refinement and leading to more accurate boundary description. Verification of the aerodynamic noise problem in the flow around a cylinder at a low Reynolds number shows that the characteristics of lift and drag， the evolution of wake shedding vortex and the near-field and far-field noise propagation characteristics obtained by the proposed method are in good agreement with the results in the literature. The numerical accuracy of the aerodynamic sound field is improved. The effects of different aspect ratios on the generation of aerodynamic sound sources and the propagation of noise in the elliptical flow are also studied. It is found that the wake shedding vortices are alternately arranged and evolve downstream. The noise field formed is symmetrically distributed about the long axis. Its flow pattern and noise characteristics are similar to those in the flow around a cylinder， but with significantly smaller lift drag fluctuation and noise intensity. Furthermore， through sound pressure decomposition， it is revealed that the contribution proportion of the dipole sound source to the overall sound intensity decreases with the decrease of the aspect ratio， while that of the monopole and quadrupole sound sources in the wake increases， directly causing the noise propagation direction to deflect upstream.