Equipment list for noise measurement test system.

The airflow in the exhaust muffler can affect the sound propagation characteristics. In this work, For a single-cylinder diesel engine, an experimental bench was set up, and the accuracy of the simulation model was verified through the mutual comparison between the experimental data and the simulation results. the transmission loss of exhaust muffler of a single-cylinder diesel engine is analyzed numerically. In addition, the influence of airflow on the acoustic performance of muffler is studied and analyzed in detail. Finally, a finite element method, namely automatic matched layer (AML) is used to simulate the anechoic boundary conditions, and the value of transmission loss of muffler with and without airflow is calculated. Results demonstrate that: Considering the influence of airflow, the transmission loss value of the muffler shows the obvious increase in the low-frequency domain of 0–2000 Hz, particularly below 1000 Hz, with difference up to 50 dB and an average of approx. 30dB. Nevertheless, the airflow has minimal influence on transmission loss in the medium-high frequency of 2000–7000 Hz. The acoustic performance is greatly affected by the internal fluid flow, and the fluid flow is beneficial to improving the acoustic performance of mufflers, especially in the low-frequency domain. Additionally, the change of transmission loss curve is more complex when the influence of airflow is considered. The research results of this work provide a more accurate prediction method on the transmission loss in practical application, and of reference significance for future studies on the acoustic performance of mufflers.

排气消声器内部的气流会对声波的传播特性产生影响。本研究针对单缸柴油机搭建了试验台架，并通过试验数据与仿真结果的对比验证，确认了仿真模型的准确性，随后对单缸柴油机排气消声器的传声损失（Transmission Loss）开展了数值分析。此外，本研究还深入探究并详细分析了气流对消声器声学性能的影响。最后，本研究采用有限元法中的自动匹配层（Automatic Matched Layer, AML）模拟无回声边界条件，分别计算了存在气流与无气流工况下消声器的传声损失值。研究结果显示：在考虑气流影响的情况下，消声器的传声损失在0~2000Hz的低频域内呈现显著提升，尤其在1000Hz以下频段，最大差值可达50dB，平均差值约为30dB。但气流对2000~7000Hz的中高频域传声损失的影响则相对微弱。消声器的声学性能受内部流体流动的影响显著，而流体流动可有效改善消声器的声学性能，尤其在低频域中这一效果更为突出。此外，当考虑气流影响时，传声损失曲线的变化趋势更为复杂。本研究的成果可为实际工程应用中的传声损失预测提供更为精准的方法支撑，同时也为后续消声器声学性能的相关研究提供了重要参考价值。