基于三维时域CFD方法的穿孔元件声阻抗提取与特性分析

The perforated components are widely used in the duct silencing devices to improve the acoustic attenuation performance in special frequency range and to reduce the flow resistance loss. In order to predict accurately the acoustic attenuation performace of duct silencing devices, the acoustic impedance of perforated compenents needs to be obtained first. In view of the complex sound and flow fields near the perforates, as well as the existence of flow-acoustic coupling and non-linear effect, the determination of perforate impedance in the presence of gas flow became an important project with engineering applications and theoretical significance. The present work will employ the 3-D time-domain CFD approach as the computational tool, the time histories of pressures and velocities in the both sides of the perforated component are aquired through the simulation of propagation of a pulse signal enforced on the steady flow, then the corresponding frequency-domain signals are obtained by using FFT, and finally the perforate impedance are extracted with the acoustic theory. Based on the computational results, the effects of medium temprature, flow status, perforated structure and sound-absorbing material on the acoustic impedance of perforates are analyzed, and then expressions for acoustic impedance of perforates are proposed suitable for the frequency-domain computations. The advantage of the project is that the effects of complex gas flow and non-linear behavior of large amplitude wave on the acoustic impedance of perforates may be considered, therefore the accurate results are obtained. To verify the computational method and results, the experimental measurements will be conducted in the presence of gas flow.

穿孔元件在管道消声装置中广泛使用，用于改善特定频率范围内的消声性能以及降低流动阻力损失。为精确预测管道消声装置的消声性能，首先需要获得穿孔元件的声阻抗。由于穿孔附近的流场和声场复杂，且存在流声耦合和非线性效应，因此获取气体流动状态下穿孔元件的声阻抗成为一项具有工程应用价值和理论意义的研究课题。本项目拟使用三维时域CFD方法作为计算工具，通过模拟计算施加在稳态流基础上的脉冲信号的传播过程来获取穿孔元件两侧的压力和速度时域历程，然后通过FFT变换得到相应的频域信号，进而结合声学理论提取出穿孔声阻抗。基于计算结果，分析介质温度、流动状态、穿孔形状、吸声材料等对穿孔声阻抗的影响规律，整理出适用于频域声学计算的穿孔声阻抗表达式。本项目的特点是能够考虑复杂气体流动和大幅波非线性效应对穿孔声阻抗的影响，从而获得精确的计算结果。为验证计算方法和结果的正确性，开展有流条件下穿孔元件声阻抗的实验测量研究。

穿孔元件广泛应用于管道消声装置中，通过阻抗失配和能量耗散来改善特定频率范围内的消声性能。作为进、排气消声系统的组成部分，穿孔元件的声学特性不可避免地会受到气体流动的影响。为了精确计算管道消声装置的消声性能，首先需要获得较为准确的穿孔声阻抗，因此获取气体流动状态下穿孔元件的声阻抗成为一项具有实际工程应用背景和理论意义的研究课题。.根据穿孔元件附近的气体流动状态，分别研究掠过流、通过流以及掠-通混合流作用下穿孔板的声阻抗。详细研究了流动马赫数、穿孔率、穿孔板厚度与小孔直径比以及雷诺数对掠过流、通过流无量纲声阻抗的影响规律，进而利用数值拟合给出了掠过流、通过流状态下穿孔板声阻抗的计算公式。计算了不同掠过流和通过流共同作用下穿孔板的声阻抗，分析了穿孔板声阻抗随频率的变化规律，从而得出混合流条件下穿孔声阻抗的一般适用性结论。.结合声学理论给出了有吸声材料贴附的穿孔板声阻抗表达式，搭建了消声器声学性能测量实验台架，利用两负载方法测量了穿孔管阻性消声器的传递损失。研究了大幅波作用下穿孔元件的声学特性，并且使用基于线性Navier-Stokes方程的频域有限元方法计算了穿孔管消声器的传递损失。