调制气流声源气声转换过程模型研究

Numerical model research for the sound energy conversion in air-modulated speaker

为克服已有准稳态理论在高频低速条件下性能预测的偏差和在换能机理假设上的不足,同时为设计者提供预示声源结构与辐射特性之间关系的工具,提出了基于混合气动声学方法的辐射声场仿真模型,分析了典型工况下流场和声场特性,探讨了换能过程的频率相关性。内流场由瞬态可压缩雷诺时均方程描述,SSTk-ω湍流模型耦合增强壁面函数用于预测喉道壁面流动分离,动网格用于对音圈调制运动建模,FW-H积分计算近距离强声场,讨论了模型关键参数的选取原则。稳态流场计算与实验结果具有较好一致性,气动声场基频与调制频率一致,声信号存在非线性谐波失真。调制频率对换能机理有影响,高频调制下涡流和剪切层的增强使得声场预测中需考虑高阶极子源的贡献。

The numerical model of air-modulated speaker（AMS）based on the hybrid computational aero-acoustics （CAA）method is proposed to overcome quasi-steady theory limitation in high frequency and low chamber pressure conditions and provide analysis tool to relate engineering designs with characteristics in radiation field.Characteristics in both fields at typical working condition are analyzed.Frequency dependence in energy conversion process is emphasized. The internal flow of AMS is described by unsteady Reynolds-averaged Navier-Stokes（RANS）equation,shear-stress transport（SST）κ-ωturbulence model is coupled with enhanced wall treatment to predict flow separation in the vocal tract,the dynamic mesh technique is utilized for modeling of voice coil modulation,and porous Ffowcs Williams and Hawkings（FW-H）integral is used for near field acoustic calculation.Primary parameters are properly selected in compressible flow,dynamic mesh,near-wall mesh generation,boundary condition,and acoustic analogy to make unsteady flow and acoustic field accurate.Agreement in steady flow is obtained between simulation and experiment results. Predominant frequency in acoustic signal is basically consistent with modulated function,and harmonic components due to nonlinearity are evident.Compared to the low frequency case,vortex evolution and free shear layer presence make dipole and quadrupole sources unable to be neglected in corresponding acoustic field prediction.