含流速聲學影響之消音器傳輸損失研究

A Study of Transmission Loss for Mufflers with Flow Acoustic Effects

康晉誠(Kang Chin-Cheng)

指導教授 ： 林章生

國立屏東科技大學/工學院/車輛工程系所/碩士(2021年)

https://doi.org/10.6346/NPUST202100352

摘要

本研究係應用傳輸損失於消音器之性能評估，提出一使用四極參數理論為基礎的麥克風變換位置傳輸損失量測法；同時援引雙麥克風轉移函數法降低頻率響應函數(FRF)相位不符造成的量測誤差。本研究使用LabVIEW開發傳輸損失演算法，並利用單膨脹室、入口延伸膨脹室及亥姆霍茲共振腔的無流速的量測結果，比對理論解及有限元素分析(FEA) 以驗證演算法的有效性。然而，原始的傳輸損失量測並未考慮流體速度，與消音器的實際工作狀態並不一致，因此本研究將進行含流體速度的傳輸損失量測。在本研究完成無流速條件的演算法驗證後，將進行含流速條件的傳輸損失量測，並與無流速的量測結果比對，確認流速對傳輸損失量測的影響；最後應用在實際市售車輛的空氣濾清器總成。經過無流速和考慮流速條件的實驗結果顯示，因流速影響，亥姆霍茲共振腔的傳輸損失效果會有顯著的降低，且共振頻率亦有偏移的現象。單膨脹室和入口延伸膨脹室因流速影響，造成傳輸損失效果提升，唯獨入口延伸膨脹室在四分之一波長共振腔的共振頻率有不同影響，在共振頻率的傳輸損失效果降低。實際運用在空氣濾清器總成，可以發現亥姆霍茲共振腔因管道結構的變化，產生不同的流速影響。

關鍵字

有限元素分析 ； 傳輸損失 ； 四極參數 ； 流速條件 ； 傳遞矩陣法

並列摘要

This study is the application of transmission loss (TL) to the performance evaluation of mufflers. We use four-pole parameters of an aeroacoustic element to propose a microphone position-change method for TL measurement. To reduce phase change of frequency response function (FRF) from measurement, the dual-microphone transfer function method is used. We employ LabVIEW to develop a TL measurement program, and measure TL performance about the Helmholtz resonator, the single expansion chamber and the extended inlet expansion chamber without flow velocity, and compare the difference between the experimental data, theoretical solutions and finite element analysis (FEA) results. However, due to the inconsistency of the operation condition of the practical mufflers, the study focuses on the influence of TL with flow velocity. We carry out the TL measurement with and without flow velocity, and confirm the influence of the flow velocity on the TL measurement. Furthermore, we apply the TL measurement in the air cleaner of commercial vehicles. The experimental results show that the influence of flow velocity on TL at the Helmholtz resonator significantly reduce and the resonance frequency shift, while the TL of single expansion chamber and the extended inlet expansion chamber increase because of the flow velocity. When measuring the TL of the air cleaner, we can find different effects of the Helmholtz resonator due to the various pipe structures.

並列關鍵字

finite element analysis ； transmission loss ； four pole parameters ； flow velocity conditions ； transfer matrix method

參考文獻

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[2] M. L. Munjal, and A. G. Doige, 1990, “Theory of a Two Source-location Method for Direct Experimental Evaluation of the Four-pole Parameters of an Aeroacoustic Element,” Journal of Sound and Vibration, Vol. 141, Iss. 2, pp.323-333.

[3] ASTM International, 2006, “Standard Test Method for Impedance and Absorption of Acoustical Materials Using a Tube, Two Microphones, and a Digital Frequency Analysis System,” ASTM E1050-98, United States.

[4] ASTM International, 2019, “Standard Test Method for Normal Incidence Determination of Porous Material Acoustical Properties Based on the Transfer Matrix Method,” ASTM E2611-19, United States.

[5] 鄔詩賢，黃敏祥，2014，「排煙消音器之聲學性能與結構參數之研究」，第二十二屆中華民國振動與噪音工程學術研討會，彰化。