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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.
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.
CDA 인입공기 증발냉각을 통한 압축기 성능 개선장치 개발 연구
김규완(Heuy Dong Kim),박진욱(Jin Ouk Park),김희동(Heuy Dong Kim) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.11
CDA(Clean Dry Air) System 에서 공기 압축기는 핵심 설비이자 소비되는 전력의 대부분을 차지한다. 그리하여 압축기 성능(ECI)을 개선함으로써 CDA System 전체성능을 크게 향상 시킬 수 있다. 종래의 많은 연구를 통해 인입공기의 온/습도 조건이 압축기에 미치는 영향에 대해 잘 알려져 있으나, 본 연구에서는 인입공기의 조건에 따라 소비되는 실제 전력 및 토출유량의 상관관계를 조사하였다. 또한 증발 냉각장치를 설치하여 인입공기 조건의 다양한 변화를 통하여 압축기성능에 미치는 영향을 연구하였다. 얻어진 결과로부터 인입공기의 온/습도가 낮을수록 압축기성능이 개선되었고, 증발냉각장치를 설치하였을 때 압축기성능이 개선됨을 알았다. In the present study, water vapor is injected at various positions in a Clean Dry Air (CDA) system such as a system inlet duct, compressor inlet, and compressor outlet by humidified air turbines. The application of evaporative cooling reduces the compression work and enhances the Energy Consumption Index (ECI) per unit volume. The main purpose of this study is to investigate the compressor power performance with different inlet air temperatures and humidity conditions. It is found that the actual power consumption and discharge flow are significantly influenced by the inlet air temperature as well as relative humidity. The results obtained during this study are compared both numerically and experimentally and are found to be in very good agreement.
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.
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/>