可變腔體槽孔型設計於管道聲場之消音性能分析

Abstract

本研究主要探討聲音經過槽孔型結構時，因其相關的幾何參數對聲音衰減的影響。本文以聲場模擬軟體為平台，共振腔體積為參數，設計出可變腔體的共鳴型消音器，並針對槽孔型圓管進行非耦合情況下的穩定流場分析。 實際進行管道消音或消音器設計時，通常會在管道內部或隔板上設計許多孔洞來減少流體的阻力及增加消音的效果。也因為這些小孔的存在，導致有限元素網格建模的困難。本文使用傳遞導納的觀念，間接模擬這些小孔的存在，故於建模時可以忽略這些小孔。因此，進行聲學計算時，在穿孔板兩側邊的網格間，定義這種傳遞導納的關係，藉此模擬這些穿孔板的小孔。 本文對不同共振腔體的消音器進行模擬及實驗分析，結果顯示，隨著共振腔體積增加，消音器的主要消音頻帶會往低頻移動。而本文也發現，同時使用兩個共振腔體，消音器的消音性能有疊加效果；即單一腔體只能消除某一頻率的噪音，同時使用雙腔體便能消除兩個不同頻率的噪音。

This study is to concentrate on the influence of structure parameters on the acoustic attenuation when the sound passes through perforated muffler. This study is to use acoustic simulation package as basis and the chamber of silencer as parameter to design some resonant muffler with variable-chamber, and make acoustic simulation on a perforated duct in an uncoupled steady fluid flow. In actual duct silencer or muffler design, the design is adopt a lot of holes to reduce the internal resistance of the fluid or increase attenuating effect. Due to the existence of holes, it resulting in difficulties in modeling finite element mesh. This study uses the concept of transfer admittance, which indirectly simulates these small holes such that being neglected while modeling. Therefore, in order to simulate those holes of perforated plate, the relationship of transfer admittances among the side edges of perforated plate grid must be defined when making acoustic calculation in progress. This study makes simulation and experiment for various chamber. The result of study shows that when the volume of chamber of muffler becomes greater, its main effectiveness will exist at lower frequency. Meanwhile, this study also found that, while two chambers of different types are used in the silencer, the performance of silencer have synergistic effects. That means one chamber eliminates a single frequency noise, but dual chambers can eliminate noises at different frequency.