非定常流场和声场有限元内燃机排气消声器研究

 消声器是降低内燃机排气噪声的主要部件。通过设计独立测试排气噪声的台架实验，分析了安装消声器前后的排气频谱特征，对比期望的噪声评价曲线，得到了消声器性能不足的频段主要集中在中高频。根据流体和声学的基本理论，基于三维数值有限元，分析了复杂消声器非定常流动状态下其压力场、温度场、再生噪声场分布和主要贡献的噪声频段，研究了消声器在稳态下的传递损失；通过研究声学传递过程中的空腔模态特征，找到了影响消声效果的主要因素。基于消声器仿真模型，研究了消声单元结构特征与消声性能之间的关系，通过改善复杂消声器的小孔结构和增加吸声材料，采取实验对比分析了插入损失，验证了分析和改进的有效性。本文综合分析了流体、声学以及流体对声学的影响，研究了内燃机排气消声器性能，此系统方法能更全面地了解和改进排气噪声。

Research of Engine Exhaust Muffler Based on Finite Element Analysis of Acoustic and Unsteady Viscous Flow

The muffler is the main component to deal with the exhaust noise of an engine. Based on the designed bench, the spectral characteristics of the exhaust noise before and after installing the muffler are analyzed and compared to the expected NR curve, to find the bad frequency bands of the muffler performance. According to the theory of the fluid mechanics and the acoustics, based on the finite element analysis, the performances of a complex muffler in the unsteady viscous flow state are analyzed, including the pressure field, the temperature field, the flow regeneration noise field and the major frequency band of the regeneration noise, meanwhile, the transfer loss in the steady-state and the acoustic-mode of the air is obtained. It is shown that the flow regeneration noise is the major factor to deteriorate the high-frequency muffler performance. Based on the numerical model analysis of the muffler, the relation between the structure characteristic of its simple cavity and its muffler performance is obtained, and the special perforated structure of the muffler can be improved and the sound-absorbing materials are also selected. Through testing of the bench, the insert losses of the original and improved mufflers are obtained, which shows that the above analysis is reliable.