Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/1969
標題: 具有流場之突張式消音器性能的實驗研究
Experimental Study on the Performance of Expansion Type Silencer with Flow
作者: 吳孟齋
Wu, Meng Jai
關鍵字: Sudden Expansion Type Silencer;突張式消音器;noise;Jet Flow;噪音;射流
出版社: 機械工程學系
摘要: 
本文主旨在探討具有流速的突張式消音器結構對整體消音系統的影響,並
建立一套方便可行的實驗方式。期能簡化消音器的性能分析過程,並了解
消音器的回饋效果對上游的影響。實驗的流場可視化是以鋁粉及油煙配合
雷射切光進行,以了解消音器內部流場結構。實驗的進氣基頻其頻率範圍
在1 Hz∼120 Hz之間,突張式消音器之擴張比H/Hi = 7.5。
針對消音器性能的量測,本實驗採用速度量測、壓力量測以及噪音量測。
實驗結果證實:在低於120 Hz的頻率範圍內,三種不同的量測方式可獲得
相似的結果。因此,建議以消音器內的單點壓力量測從事消音器性能及排
氣系統整體性能的研究。另外,具有實際流場的消音器與上游噪音源(如
引擎)在整個系統中是互相影響的,所以消音器的性能必須根據所搭配的
消音對象(如某種引擎)作整體性能的量測才能獲得具體的性能表現。
實驗結果亦顯示:消音器出口下游的噪音包含由消音器內傳出的低頻噪音
以及由出口射流等其他因素所產生的高頻噪音。消音器內之擾動壓力僅對
應於消音器出口下游的噪音的低頻部分。所以,要消除排氣噪音除了要考
慮消音器內部的流場結構外,還要改善消音器的出口流場結構,以降低由
於消音器出口的射流造成額外的高頻噪音。

The purpose of this study is to investigate the performance of
sudden expansionsilencer on the engine exhaust system and to
suggest a simple experimental method for this evaluation .
It is expected to simplify the evaluation processof sudden
expansion silencer and understand the feedback interaction
between the silencer and the upstream system. Qualitatively,
laser sheet flow visualization is employed to reveal the
instantaneous flow structure inside andat the exit of the
silencer. Furthermore, the fluctuating energy of the
velocity, the pressure and the sound level are related while the
inflow frequency range from 1 Hz to 120 Hz.
It is found that the frequency response of the fluctuating
energy of the velocity and pressure are closely linked to
the sound level measured downstreamof the exhaust system. This
suggests that the frequency response of the one-location
pressure measurement inside the silencer be a simple way that
can greatly reduce the time for evaluating the silencer. When
the flow is present,the silencer and its upstream system should
be thought as a unit to faithfully reveal the performance of the
whole system. Sound level
measured far downstream of the silencer includes the low
frequency flow tone induced inside the silencer and the high
frequency noise generated bythe exhaust jet flow. Therefore,
modification of the flow structure inside thesilencer will
change the low frequency flow tone, whereas the high frequency
noise level can be improved by manipulating the exhaust jet flow
structure.
URI: http://hdl.handle.net/11455/1969
Appears in Collections:機械工程學系所

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