基于基尔霍夫面的四维声学频域公式

流动诱发噪声问题是实际工程领域极为普遍的问题之一,经典的声比拟模型仅以声学压力为参考来评估声场特征分布还远远不够。从声压和声学速度矢量为变量的四维线性波动方程出发,选择包围非线性声源的基尔霍夫面为积分面,并结合对流格林函数,给出均匀运动介质的四维声学频域积分公式;针对静止、旋转单极子源和偶极子源开展数值预测研究。结果表明：本文获得的声压和声学速度分布与解析解吻合,均匀来流情形下静止点源的声场分布表现出典型的对流效应;受均匀来流、点源的自激频率、谐波阶次和旋转频率的共同影响,旋转点源的声场分布则表现出明显的多普勒效应和对流效应。本文对均匀流矢量气动噪声开展的精细化研究能够为声能量的评估和传输路径预测提供技术支撑,进一步为降噪研究提供理论依据。

Four-dimensional formulation of the acoustic frequency domain for Kirchhoff"s surfaces

Flow-induced noise is a common problem in practical engineering. The classical acoustic analogy model is insufficient to evaluate the characteristic distribution of the acoustic field using only acoustic pressure as a reference. This paper starts from a four-dimensional linear wave equation with sound pressure and sound velocity vectors as variables, by choosing the Kirchhoff surface to enclose a nonlinear acoustic source and combining with the convective Green"s function, the four-dimensional acoustic frequency-domain integral equation for a uniformly moving medium is developed. Numerical prediction studies were conducted for stationary, rotating monopole and dipole sources. The results indicate that the distributions of the sound pressure and acoustic velocity obtained by the present proposed method are in good agreement with the analytical solutions. In contrast to the stationary flow case, the acoustic field distribution of the stationary point source in the uniform flow exhibits a convection effect. On the other hand, the acoustic field distribution of the rotating point source exhibits a strong Doppler effect and convection effect due to the joint influence of the uniform flow, the self-excitation frequency, harmonic order, and rotational frequency of the point source. The refined study of aerodynamic vector noise with uniform flow in this paper can provide technical support for the assessment of acoustic energy and the prediction of transmission paths. Additionally, it provides a theoretical basis for noise reduction studies.