飛機引擎消聲室之微沖孔板熱流聲音穿透損失模擬計算

Calculation of Aero-Acoustics Transmission Loss for Micro Perforated Panel (MPP) Muffler Inside A Hush-House Chamber

黃田子(Tian-zi Eng)

指導教授 ： 沈永堂 ； 陳炯堯

朝陽科技大學/設計學院/建築系建築及都市設計碩士班/碩士(2013年)

摘要

微沖孔板(Micro Perforated Panel，MPP)之微小孔隙建立在亥姆霍茲共振原理(Helmholtz Resonance) 之聲音衰減的基礎上，其運用介於各種不同大小的工業消聲管以及機械用物如：汽機車、冷氣機及排風管等。

在一般的情況之下，MPP吸音率可使用Maa(1975)的預測理論進行推導計算，或是以實測方法及模擬方式獲得MPP聲壓之消聲係數。然而，在板面具有熱流傳導時，聲音穿透損失(Sound Transmission Loss，STL)計算將變得更爲複雜。Munjal (1986)提出空調冷氣機之格柵式消聲管的比例運用及計算方法；此外，於2003年提出MPP的簡化計算公式。然而，其計算公式僅有低頻率部分趨近消聲管之實測值，並無法正確計算中高頻率部分。

因此，本研究以探討在具有高速流體及溫度差異的空間下，T-10飛機引擎消聲室之MPP對熱流環境之STL的影響。其目的除使消聲室順利排出内部空間的熱流以及導入冷空氣之外，更在於消除大量的噪音源。爲此，計算公式將以三大項主因為計算條列：一、格柵式消聲室之尺度；二、MPP之各項尺度；三、消聲室環境條件。

本研究使用邊界元素法(Boundary Element Method，BEM)之轉矩陣公式為減噪流程之理論推導，以達到計算流體聲場透過MPP之STL值。最後，本研究發現：一、氣流方向(z,m) 對材質及空間阻抗佔據極大的因數；二、 以各頻率波數〖(K〗_(z,m))之密度導向材質密度方能正確的計算中高頻率；三、空間變項S⁄P能夠取得平衡值介於3~4之間，即屬於較良好的格柵式飛機引擎消聲空間。

關鍵字

轉矩陣 ； 邊界元素法(BEM) ； 聲音穿透損失(STL) ； 熱流傳導 ； 微沖孔板(MPP) ； T-10飛機引擎消聲室

並列摘要

Micro Perforated Panel (MPP) has tiny pores which attenuates sound decay based on the Helmholtz resonance. It can be used in various sizes of industrial muffler pipe and mechanical purposes, such as motor vehicles, air conditioner, exhausting pipe, etc.

Generally, the sound absorption coefficient of the MPP was predicted by Maa (1975). It has been able to obtain the sound pressure coefficient by measuring method or simulation. However, the calculation of sound transmission loss(STL) becomes more complicate when a panel surface is with a thermal flux. Munjal (1986) proposed the computation method of air conditioner pod silencer. In addition, Munjal(2003) also proposed a simplified formula of MPP. Nevertheless, the formula is only approach measure values in low frequency but it is unable to calculate the section of high frequency in the pod silencer.

Therefore, this study is to explore strategy for evaluating the aero-acoustics transmission loss for MPP inside a T-10 Hush-House chamber. It’s proposed to favorably the thermal flux and importing the air conditioning as well as eliminates the noise sources. Therefore, the regulation of calculation is in three items: 1.Dimension of the anechoic chamber. 2. Different scales of MPP. 3. The environmental conditions of the anechoic chamber.

This study applies the formulation of the boundary element method (BEM) in transfer matrix for the process of theoretical derivation to achieve the simulation of STL through a MPP. Finally, this study finds that 1. The direction of wave number 〖(K〗_(z,m)) takes a significant factor to control the impedance of material and spatial. 2. The proper calculation of the high frequency is in order to wave number〖(K〗_(z,m)) of each frequency velocity direct to material density. 3. The favorable proportion of anechoic chamber at T-10 Hush-House is between 3 and 4 by S/P.

並列關鍵字

Transfer matrix ； Sound Transmission Loss(STL) ； Boundary Element Method (BEM) ； Thermal Flux ； Micro Perforated Panel (MPP) ； T-10 Hush-House

參考文獻

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