쐐기소리에 관한 실험적 연구 = Experimental Study on the Edge-tones

다국어 초록 (Multilingual Abstract)

Edge-tones are generated by a plane jet impinging on a wedge. Although a number of investigations with various wedges and nozzles have been performed, they are for low speed or supersonic jets with the purpose of confirming the Powell's feedback model.
Thus, the objective of this paper is to measure the frequency characteristics, unstable region, unstable modes, convection velocities, directivity of edge-tones in the range of subsonic jet velocities. The experiment is performed by varying velocities and impinging distances for a slit nozzle and a sharp edged wedge in the central plane of the jet.
It is found that impinging tones are generated in all subsonic velocities, but the characteristics of tones are found to be shifted around Re?14000, probably due to the transition of the shear layer from laminar to turbulent flow. The frequencies decreased with the Reynolds number and the impinging distance. The sound pressure level increases with the Reynolds numbers, but its maximum value is almost constant for Re≥ 10000. It is found that the unstable modes of plane jet are completely asymmetric. The directivity of the radiated sound is dipole-like with some shift to the downstream direction due to the jet stream. Convection velocities ratios were increased with Strouhal number and asymptotically decreased with stage number.

목차 (Table of Contents)

• Ⅰ.서론
• Ⅱ.선행연구와 관련이론
• 1.유동소음
• 2.되먹임(feedback) 모델
• 3.제트의 불안정
• 4.저속 충돌음
• 5.고속 충돌음
• Ⅲ.실험
• Ⅳ.실험결과 및 고찰
• 1.충돌음의 주파수 특성
• 2.충돌음의 음압 및 지향특성
• 3.충돌제트의 불안정특성
• Ⅴ.결론