Abstract: The acoustic modes of elliptical and oval expansion chambers are calculated using the finite element method, and the effects of inlet and outlet locations on the acoustic attenuation characteristics of the expansion chambers are studied. The numerical results show that the first propagation mode for the concentric expansion chambers is the third mode. The effect of the third mode can be eliminated by locating the outlet on the nodal line of this mode, and with this method the range of plane wave can be expanded and the acoustic attenuation performance of the expansion chambers can be improved. For the expansion chambers with offset inlet and outlet, the first mode is excited and the three-dimensional wave effects appear at lower frequencies, and the acoustic attenuation performance becomes poorer in the middle frequency range.

Key words: acoustics, elliptical expansion chambers, oval expansion chambers, acoustic mode, acoustic attenuation characteristics

摘要： 使用有限元法计算椭圆形和跑道圆形截面膨胀腔的声学模态，分析进出口管位置对膨胀腔消声特性的影响。结果表明，同轴膨胀腔的第一个可传播的高阶模态为第3阶模态，出口置于该模态的节线处，可以消除该阶模态的影响，使平面波频段拓宽，膨胀腔的消声性能得到改善。进出口管偏置的膨胀腔，第1阶模态被激发，三维波效应在较低频率出现，中频消声性能变差。

关键词: 声学, 椭圆形截面膨胀腔, 跑道圆形截面膨胀腔, 声学模态, 消声特性