Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/2746
標題: 突張式消音器內流場與壓力場之研究
Experimental Study of Flow Structure and Pressure Distribution Inside Sudden Expansion Silencer
作者: 胡志鋒
Hu, Chih Feng
關鍵字: sudden expansion silencer;突張式消音器;noise;pulsating inflow;噪音;脈衝入流
出版社: 機械工程學系
摘要: 
本文主旨在探討具有週期性脈衝入流對突張式消音器整體消音性能的影響,並且分析消音器內部流場結構與壓力場之關係。實驗的進氣頻率範圍在10 Hz ~ 120 Hz之間,突張式消音器之擴張比為7.5。分別改變消音器進排氣管之長度、不對稱度、孔隙比、伸入消音器內部之長度與進氣管尾端凸緣之長度等參數,以了解各項參數對單共振腔與雙共振腔消音器整體消音性能之影響。本實驗利用極細之鋁粉配合雷射切光進行流場可視化,使用熱線測速儀量測消音器內部定量之速度變化,並量測消音器內部的壓力以了解消音器內部流場結構與壓力場之關係。
實驗結果顯示:在單共振腔的消音器中,在進氣管之尾端加上適當長度的凸緣則可大幅改善消音器之消音性能。若將消音器進出口管之不對稱度加大時,對於低頻域(80 Hz以下)之噪音亦可獲得改善,但會稍微增加高頻域(90 Hz以上)之噪音。增加進排氣管伸入消音器內部之長度與進排氣管之長度時,則可以改變消音之頻段。然而,增加進氣管之長度後,會使100 Hz以上之噪音量明顯增加。在雙共振腔的消音器中,縮小消音器中央直管通道之高度,可以使100 Hz以下之噪音量明顯降低,同時亦會使100 Hz以上之噪音稍微增強。若縮短進排氣管伸入消音器內部之長度,則可以降低110 Hz以上之噪音。此外,使用具有30 % 孔隙比之進氣管時,則可降低50 Hz以下以及110 Hz以上之噪音。若使用具有30 % 孔隙比之排氣管時,僅會增強30 Hz與70 ~ 90 Hz等頻率範圍之噪音。

This study investigates the performances of sudden expansion silencer under periodic inflow, ranging from 10Hz to 120Hz. The expansion ratio of the silencer model is 7.5. Such parameters are the length and the asymmetry of inlet and outlet duct, the length of inlet and outlet ducts into silencer, the effect of inlet duct flange as well as the porosity ratio. Further, laser sheet flow visualization is employed to reveal the instantaneous flow structure near the exit of the inlet duct. The velocity measurement by hotwire is related to the fluctuating pressure inside the silencer while the inflow frequency range from 10Hz to 120Hz.
For a single expansion-chamber silencer, suitable length of inlet duct flange can reduce effectively the sound level. The asymmetry of the inlet and the outlet duct can eliminates the noise level at frequencies lower than 80Hz. On the other hand, the noise level increases slightly at frequencies higher than 90Hz. Changes of the lengths of the inlet and the outlet ducts into the silencer can slightly modify the natural frequency of the fluid oscillator inside the silencer. Further, increasing the lengths of the inlet and the outlet ducts can lower the natural frequency of the silencer and eliminate the noise level within specific frequency range. However, longer length of the inlet duct can increase the noise level at frequencies higher than 100Hz. For a dual expansion-chambers silencer, small height of the connecting duct can reduce the noise level at frequencies lower than 100Hz. The inlet duct with 30% porosity ratio can reduce the noise level at frequencies below 50Hz and above 100Hz. On the other hand, the outlet duct with 30% porosity ratio can increase the noise level at frequencies 30Hz and 70~90Hz.
URI: http://hdl.handle.net/11455/2746
Appears in Collections:機械工程學系所

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