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고속철도 터널출구로부터 방출되는 충격성 소음에 관한 모형실험
김희동,이종수,신현승 安東大學 1995 安東大學 論文集 Vol.17 No.1
As a railway train enters a tunnel at high speed, a compression wave is formed in front of the train and propagates along the tunnel. The compression wave subsequently emerges from the exit of the tunnel and generates a pulse wave, which causes an impulsive noise. In order to clarify the acoustic characteristics of the noises, in the present study experiment was carried out by using the pulse waves emitted from an open end of a shock tube. Various pulse waves were obtained by controlling the compression wave formed in the tube. The results show that as the compression wave formed at tunnel exit becomes strong, the pulse wave emitted propagates with strong directional characteristics forward the axial direction of the tube, and that attenuation of the pulse wave propagating a ground surface can be reasonably predicted by a linear acoustic theory. Furthermore, the impulsive noise at far-field from the tube exit results in a sound level reduction of 6dB with a doubling of the propagating distance.
김태호,이영기,이호준,김희동 安東大學 1996 安東大學 論文集 Vol.18 No.1
Many real flows through supersonic nozzles essentially include viscous friction, heat transfer, and also mass bleed in some cases. Frequently these make a prediction for the nozzle flow difficult as well as an engineering design for the nozzle impossible. The objective of the present study is to present a simple analytical method available to design a supersonic nozzle or diffuser. Wall friction, heat transfer, and mass addition/bleed are involved to one-dimensional calculation for an isentropic flow with area change. It is found that sonic point is not always located at the geometrical throat of supersonic nozzle. This result is very important for determining the critical mass flow rate through the nozzle and thrust. One interesting result shows that shockless transition from supersonic flow to subsonic flow is theoretically possible for a real nozzle flow.
Propagation Characteristics of Compression Waves Reflected from the Open End of a Duct
Heuy Dong Kim,Dong Hoon Lee,H. kashimura 대한기계학회 2003 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.17 No.5
The present study addresses the distortion of the compression wave reflected from an open end of a shock tube. An experiment is carried out using the simple shock tube with an open end. Computational work is also performed to represent the experimented flows. The second-order Total Variation Diminishing scheme is employed to numerically solve the unsteady, axisymmetric, inviscid, compressible governing equations. Both the experimented and predicted results are in good agreement. The generation and development mechanisms of the compression wave, which is reflected from the open end of the shock tube, are obtained in detail from the present computations. The effect of size of the baffle plate at the open-end that causes the reflection of the incident expansion wave is found negligible. A good correlation is obtained for transition of the reflected compression wave to a shock wave inside the tube. The present data show that for a given wave length of the incident expansion wave the transition of the reflected compression wave to a shock wave can be predicted with good accuracy.