• Title, Summary, Keyword: 팽창파

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Numerical Simulation of Axisymmetric Supersonic let Impingement on a Flat Plate (수직평판에 충돌하는 축대칭 초음속 제트의 수치 연구)

  • 신완순;이택상;박종호;김윤곤;심우건
    • Journal of the Korean Society of Propulsion Engineers
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    • v.4 no.3
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    • pp.11-18
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    • 2000
  • When supersonic underexpanded jets are exhausted from the nozzle, complex shock cell configurations such as barrel shock, expansion fan, Mach disc, and exhaust-gas jet boundary are appeared repetitively. The shock cell is smeared by turbulence dissipation and disappeared in long distance from the nozzle. When underexpanded jet is suddenly impinged on a flat plate, it forms very complex flow structure. In this paper, we solve compressible Wavier-Stokes equation adapting finite volume method to obtain jet impingement flow structure and compare calculated data with experimental ones. It is shown that numerical simulation data are in good agreement with experimental one in a short distance between nozzle exit and flat plate and little influence of underexpanded ratio is appeared in jet impingement now distribution.

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Characteristics Method Analysis of Wind Pressure of Train Running in Tunnel (터널을 주행하는 열차의 풍압에 대한 특성해법 해석)

  • Nam, Seong-Won;Kwon, Hyeok-Bin;Yun, Su-Hwan
    • Journal of the Korean Society for Railway
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    • v.15 no.5
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    • pp.436-441
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    • 2012
  • Pressure waves are generated and propagate in tunnel when train enters a tunnel with high speed. Compression wave due to the entry of train head propagates along the tunnel and is reflected at tunnel exit as expansion wave. While expansion wave due to the entry of train tail propagates along the tunnel and is reflected at tunnel exit as compression wave. These pressure waves are repeatedly propagated and reflected at tunnel entrance and exit. Severe pressure change per second causes ear-discomfort for passengers in cabin and micro pressure wave around tunnel exit. It is necessary to analyze the transient pressure phenomena in tunnel qualitatively and quantitatively, because pressure change rate is considered as one of major design parameters for an optimal tunnel cross sectional area and the repeated fatigue force on car body. In this study, we developed the characteristics method analysis based on fixed mesh system and compared with the results of real train test. The results of simulation agreed with that of experiment.

Analysis for Characteristics Method on Wind Pressure of Trains Crossing in Tunnel (터널내 교행 열차의 풍압에 대한 특성법 해석)

  • Nam, Seong-Won
    • Journal of the Korean Society for Railway
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    • v.16 no.6
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    • pp.454-459
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    • 2013
  • Pressure waves are generated and propagate in a tunnel when train enters tunnel high speed. A compression wave due to the entry of train head propagates along the tunnel and is reflected at tunnel exit as an expansion wave. An expansion wave due to the entry of the train tail propagates along the tunnel and is reflected at tunnel exit as a compression wave. These pressure waves are repeatedly propagated and reflected at the tunnel entrance and exit. Severe pressure changes causes ear-discomfort for passengers in the cabin and micro pressure waves around the tunnel exit. It is necessary to analyze the transient pressure phenomena in tunnels qualitatively and quantitatively, because pressure change rate is considered as one of the major design parameters for optimal tunnel cross sectional area and repeated fatigue force on car body. In this study, we developed a characteristics method based on a fixed mesh system and boundary conditions for crossing trains and analyzed this system using an X-t diagram. The results of the simulation show that offsetting of pressure waves occurs for special entry conditions of a crossing train.

Performance analysis of the axisymmetric mufflers by BEM (BEM을 이용한 축대칭 소음기의 성능해석)

  • 임정빈;정갑철;권영필
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.306-311
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    • 1994
  • 본 연구에서는 축대칭 형태의 음향문제를 해석할 수 있는 경계요소 프로그램을 개발하여 소음기의 투과손실(transmission loss)의 계산에 적용하였다. 우선 단순팽창관 소음기에 대해서는 경계요소법에 의해 투과손실을 구한 후 평면파이론 및 실험으로 구한 값과 비교 평가하였다. 또한, 평면파이론을 적용할 수 없는 경우로서 흡음재를 부착한 팽창관 소음기에 대해서는 경계요소법으로 구한 투과손실을 실험결과와 비교 고찰하였다.

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One-Dimensional Numerical Study of Compression Wave Propagating in High-Speed Railway Tunnel (고속철도 터널내를 전파하는 압축파의 일차원 수치해석)

  • 김희동;엄용균;송미일태
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.5
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    • pp.1280-1290
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    • 1995
  • In order to investigate the compression wave propagating in a high-speed railway tunnel, a numerical calculation was applied to the wave phenomenon occurring in a model tunnel. Unsteady, one-dimensional inviscid or viscous flows were solved by an explicit TVD scheme, and the calculated flows were compared with the results of measurement in real tunnels. Tunnel noises caused by emission of the compression wave were characterized in terms of excess pressure of compression wave, pressure gradient in the wave front and width of the compression wave. Calculated attenuation, pressure gradient and width of compression wave with the propagating distance agreed with the results of measurement in the real tunnels. The results also show that tunnel noises are proportional to the train velocity entering the tunnel.

A Study of Lateral Force Fluctuations in Over-Expanded Nozzle Flow (과팽창 노즐 유동에서 발생하는 측력변동에 관한 연구)

  • Lee, Jong-Sung;Cha, Yong-Su;Vincent, Lijo;Kim, Heuy-Dong
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.253-256
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    • 2009
  • In the present paper, experimental and numerical fundamental analyses of the occurrence of lateral force in overexpanded thrust nozzle were carried out. Investigation of the lateral force fluctuations in an thrust nozzle for the shutdown transient was presented. Wall pressure distribution and Schlieren Photographs as NPR were presented. Pressure peak is observed during transition of RSS to FSS.

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경사 평판에 충돌하는 초음속 과소팽창 제트에 관한 실험적 연구

  • 이택상;이정민;박종호;김윤곤
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.32-32
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    • 1999
  • 초음속 과소 팽창 제트가 경사진 평판에 충돌을 하게 되면 평판의 표면과 노즐출구에서 팽창된 자유제트(Free jet)와의 상호 간섭으로 인해 매우 복잡한 유동 구조가 형성된다. 예를 들면, 수직평판에서 발생되는 판 충격파(Plate shock)는 경사평판에서는 Upper plate shock, Lower plate shock, Intermediate plate shock과 같이 여러 형태로 발생되어 평판에서의 압력분포에 있어 수직일 경우와 다소 다른 경향을 보여준다. 본 연구의 주요 목적은 평판의 경사각을 변화시킬 때 평판 표면에서의 복잡한 유동 현상을 이해하는데 있다.

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A Fundamental Study of Coaxial Supersonic Jets (동축 초음속 제트유동에 관한 기초적 연구)

  • 이권희;구병수;김희동
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.37-37
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    • 2000
  • 일반적으로 노즐 입구의 압력과 배압의 비가 어떤 임계값보다 큰 경우에 축소확대 노즐을 통하는 유동은 노즐목에서 초크하며, 노즐출구에서는 용이하게 초음속으로 된다. 노즐을 통하여 초음속으로 방출되는 제트유동에 관해서는 현재까지 많은 연구가 수행되었다. 이들 연구에 의하면 노즐 압력 비에 따라 노즐출구에서의 유동상태(즉 과팽창, 적정팽창, 부족팽창상태)가 결정되며, 노즐출구로부터 하류의 초음속 제트유동에서 발생하는 충격파 구조 및 위치, 제트경계의 구조 그리고 제트의 코어 등 유동의 기구가 비교적 상세하게 알려져 있다.(중략)

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Numerical simulation on propagation of hydrocarbon flame in a deformable tube (변형하는 가스 이송관 내에서 전파하는 탄화수소화염의 수치 해석 모델링)

  • Gwak, Min-Cheol;Yoh, Jai-Ick
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.304-308
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    • 2012
  • This paper presents a numerical investigation on propagation of hydrocarbon (ethylene-air mixture) detonation in a deformable copper tube. In this study, we deal with interactions of multi-materials, gas and solid. In gas phase, the model consists of the reactive compressible Navier-Stokes equations and one step chemical reaction. Also we use Inviscid Euler equations in solid. In order to the interface tracking and the determination of boundary values, our model handle level-set and ghost fluid method. Through the numerical simulation results, we identify generations of expansion waves and interferences by the wall deformation. In addition, we predict the minimum copper tube thickness that ensures safety under an incident detonation.

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Theoretical x-t Diagram Analysis on Pressure Waves of High Speed Train in Tunnel (터널에서의 고속철도 압력파에 관한 X-t선도 이론 해석)

  • 남성원;권혁빈
    • Journal of the Korean Society for Railway
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    • v.7 no.3
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    • pp.200-207
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    • 2004
  • Theoretical study has been conducted to clarify pressure characteristics of KTX (Korea Train eXpress) in tunnel. The severe pressure change in tunnel may give rise to the ear-discomfort for passenger and fatigue for car body. Critical tunnel lengths which are induced by x-t diagram analysis can be applied to the experimental results measured by using the running test with atmospheric pressure sensors and portable data acquisition system in previous study. In this study, the tunnels from 200m to 4000m in length have been chosen for the investigation of tunnel length effects. We found that there are similar patterns of external pressure change for each critical tunnel length. The critical tunnel lengths are governed by train speed, train length and sonic velocity. And, the patterns of pressure wave in tunnel are classified into eight groups.