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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.
Numerical simulation on characteristics of particle-gas flows in supersonic impinging jet
Heuy Dong Kim(김희동),Guang Zhang,Yingzi Jin,Toshiaki Setoguchi 한국가시화정보학회 2016 한국가시화정보학회 학술발표대회 논문집 Vol.2016 No.4
The supersonic impinging jets always occur when crafts are starting short takeoff and vertical landing from the ground. The adverse flow conditions happen to decrease the performance of aircrafts, such as impinging force, high noise spectrum and high shear stresses. Due to rare results on particle-gas impinging jet flows to date, numerical simulations were performed to investigate the supersonic impinging jet flows of particle-gas two phases in the present studies. Convergent-divergent supersonic and convergent sonic nozzles were used to induce the supersonic jet flows. Discrete phase model (DPM) was used to simulate the particle-gas flows. Different particle diameters were investigated. The flow Mach number and pressure coefficients on the ground surface were obtained to describe phenomena inside impinging and wall jet flows. The particle motion was obtained in details from the present simulations.
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.
The Self-Induced Oscillations of the Under Expanded Jets Impinging Upon a Cylindrical Body
Heuy-Dong Kim,Hideo Kashimura,Toshiaki Setoguchi 대한기계학회 2002 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.16 No.11
The present study addresses the flow characteristics involved in the self-induced oscillations of the underexpanded jet impinging upon a cylindrical body. Both experiment and computational analysis are carried out to elucidate the shock motions of the self-induced oscillations and to find the associated major flow factors. The underexpanded sonic jet is made from a nozzle and a cylindrical body is placed downstream to simulate the impinging jet upon an obstacle. The computational analysis using TVD scheme is applied to solve the axisymmetric, unsteady, inviscid governing equations. A Schlieren system is employed to visualize the self -induced oscillations generated in flow field. The data of the shock motions are obtained from a high-speed video system. The detailed characteristics of the Mach disk oscillations and the resulting pressure variations are expatiated using the time dependent data of the Mach disk positions. The mechanisms of the self-induced oscillations are discussed in details based upon the experimental and computational results.<br/>