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이동훈,뢰호방총,Lee, Dong-Hoon,Seto, Kunisato 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.1
The objective of this study is to experimentally investigate the noise propagating characteristics, the noise reduction mechanism and the performance of a slotted tube attached at the exit plane of a circular convergent nozzle. The experiment is performed through the systematic change of the jet pressure ratio and the slot length under the condition of two kinds of open area ratios, 25% and 51%. The open area ratio calculated by the tube length equivalent for the slot length is defined as the ratio of the total slot area to the surface area of a slotted tube. The experimental results for the near and far field sound, the visualization of jet structures and the static pressure distributions in the jet passing through a slotted tube are presented and explained in comparison with those for a simple tube. The propagating characteristics of supersonic jet noises from the slotted tube is closely connected with the slot length rather than the open area ratio, and its propagating pattern is similar to the simple tube. It is shown that the slotted tube has a good performance to suppress the shock-associated noise as well as the turbulent mixing noise in the range of a limited jet pressure and slot dimension. The considerable suppression of the shock‘associated noise is mainly due to the pressure relief caused by the high-speed jets passing through the slots on the tube. Both the strength of shock waves and the interval between them in a jet plume are decreased by the pressure relief. Moreover, the pressure relief is divided into the gradual and the sudden relief depending upon the open area ratio of the slotted tube. Consequently, the shock waves in a jet plume are also changed by the type of pressure relief. The gradual pressure relief caused by the slotted tube with the open area ratio 25% generates the weak oblique shock waves. On the contrary, the weak normal shock waves appear due to the sudden pressure relief caused by the slotted tube with the open area ratio 51%.
[연료 및 윤활유부문] 두개의 음향센서를 이용한 차음시트의 음향투과손실 측정에 관한 타당성 연구
이동훈(Donghoon Lee),강문(Moon Kang),뢰호 방총(Kunisato Seto) 한국자동차공학회 2000 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
This study is to investigate the validity on the sound transmission loss measurement of sound isolation sheet using two-microphone in an impedance tube. The two-microphone random-excitation technique proposed by Seybert and Ross is introduced. The power reflection coefficient measurements in both closed and open tube exits were carried out to validate the influences of the microphone spacing and the distance of the first microphone from the test sample surface. It is shown that the accuracy of the measured results depends upon the microphone spacing and the distance of the first microphone from the test sample surface. The effects of the isolation sheet positions and the tube exit conditions in the impedance tube on the sound transmission loss are discussed.