- 學位論文
單腔消音器之脈衝流場與穩定流場引發噪音特性探討
Investigation on the acoustic performance of simple expansion chambers according to the pulsation flow and the steady flow excitation
摘要
本研究以流場引發噪音、脈衝流噪音及消音器本體之傳輸損失等實驗，探討不同尺寸與入、出口管配置之單膨脹室消音器之聲學性能。 在實驗中以特製之引擎平台模擬引擎排氣脈衝及其於消音器內衍生之排氣脈衝音，並以消音器尾管所量測之流體流動之壓差為依據，進行均勻無激擾之流場引發噪音之量測，最後進行消音器單體性能之傳輸損失量測。將三種量測結果進行討論比較，以探討消音器之外型尺寸設計與不同激擾條件對消音器尾管幅射噪音之影響。 在結果中可發現在排氣脈衝與穩定流場的噪音頻譜中，都以尾管共振頻率為主導；偏心旋轉型消音器因其入、出口管距離較近，會引發Helmholtz 共振現象，並可藉由旋轉角度改變，達到降低某一頻率所生之峰值；入、出口管為L形之消音器，會使各階尾管共振頻率降低；因此在使用消音器對特定頻率消音時，可由入、出口管的距離、偏心角度或是管的外形來做一設計。
並列摘要
In this research, the acoustics performance and the radiated noise characteristics of variety simple expansion reactive mufflers were discussed according to by the series flow generated noise measuring, pulsation noise measuring, and also dual-microphone transmission loss measuring. A modified engine test rig was built up for the purpose of muffler pulsation exciting radiated noise. Next, the flow generated noise test was carried on under the steady flow excitation and mass flow rate are based on the tailpipe flow pressure different form the pulsation exciting condition. Finally, the transmission loss measurement was conducted. Through three experimental results, both the pulsation exciting and the steady flow exciting conditions, the tailpipe emitted noise was dominant by the tailpipe resonant modes. The Helmoholtz modes will regard to the chamber cavity be evoked owing to eccentric allocation and the short spacing distance between the inlet and outlet tubes. A specific frequency component could be eliminated by altering the inlet and outlet tubes. Also, the use of L-shape tubes will move the tailpipe resonant mode to the lower frequency region. Thus, by changing the spacing distance, the shape or eccentric angle of inlet and outlet tubes will alter the muffler radiating noise frequency components.