• Title, Summary, Keyword: 팽창파

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Experimental and Computational Studies of FSS-RSS Phenomena in an Over-Expanded Nozzle (과팽창 노즐 내에 발생하는 FSS-RSS 현상에 관한 실험적 및 수치해석적 연구)

  • Lee, Jong-Sung;Kim, Heuy-Dong
    • Journal of the Korean Society of Visualization
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    • v.8 no.3
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    • pp.56-62
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    • 2010
  • The interaction patterns between shock wave and boundary layer in a rocket nozzle are mainly classified into two categories, FSS(Free Shock Separation) and RSS(Restricted Shock Separation), both of which are associated with the thrust characteristics as well as side loads of the engine. According to the previous investigations, strong side loads of the engine are produced during the period of transition from FSS to RSS or vice versa. The present work aims at investigating the unsteady behavior of the separation shock waves in a two-dimensional supersonic nozzle, using experimental method and CFD. Schlieren optical method was employed to visualize the time-mean and time-dependent shock motions in the nozzle. The unsteady, compressible N-S equations with SST K-$\omega$ turbulence closure were solved using a fully implicit finite volume scheme. The results obtained show the separation shock motions during the transition of the interaction pattern.

Flow Characteristics of 2 Dimensional Supersonic Nozzle in Overexpanded Conditions (2차원 초음속 노즐의 과대팽창 유동 특성)

  • 김성돈;정인석;최정열
    • Journal of the Korean Society of Propulsion Engineers
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    • v.6 no.2
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    • pp.1-7
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    • 2002
  • In the modern propulsion systems, requited thrust is obtained using a nozzle. Sometimes shock and induced boundary layer separation is generated in an over-expanded convergent-divergent supersonic nozzle. It occurs because the nozzle expansion ratio is too large for a given nozzle pressure ratio (NPR). This phenomenon can be explained that it redefines effective nozzle geometry, shorer nozzle geometry and lower pressure ratio, in a given pressure ratio. Numerical studies were conducted about a fixed geometry 2D nozzle in overexpanded condition and compared with Hunter's experimental result. For the numerical simulation of the supersonic nozzle, Navier-Stokes equations are considered and as a turbulent model, $\kappa$-$\varepsilon$ /$\kappa$-$\omega$ blended SST two equation turbulent model is used. The characteristics of $\lambda$-shape shock systems due to the interaction of shock and boundary layer was investigated in a low NPR. And the result of comparison of thrust value shows that a fixed geometry nozzle can cover required flight mission.

Motion and Wave Transmission Effect on Floating OWC(Oscillating Water Column) Wave Energy Conversion System (진동수주형 파력발전 시스템에서 운동과 파랑회절의 영향)

  • Lee, Sang-moo;Kim Seoung-gun
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • pp.20-25
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    • 2001
  • 부유식 파랑에너지 변환시스템(Oscillating Water Column)에서 에너지 변환은 입력파와 챔버, 챔버내 공기의 상호작용으로 이루어진다. 이 논문은 파랑에너지를 기계적 운동으로 변환하는 기계적 특성을 해석한다. 단일 진동수 규칙파가 입력되었을 때에 파에 의하여 챔버의 상하운동이 선형적으로 발생하며, 이 상하운동은 챔버내의 압력 변화에 영향을 받는다. 상하운동과 챔버내로 투과한 파, 그리고 챔버내 압력에 의해 발생되는 파에 의해 챔버내의 상대운동을 정하고, 그 상대운동에 의한 공기의 압축 팽창과 온도상승을 근사적 열역학적 방정식으로 해석하여 오리피스를 통한 유량과 압력을 기준으로 에너지 변환요율을 결정하였다. 얻어진 식은 간단하면서도 관련요소의 영향을 전반적으로 표현한다. 개구율 변화에 따른 운동응답을 비교하였다.

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Prandtl-Meyer Expansion Through a Small Wavy Wall of Supersonic Flow with Condensation in a Channel (유로내에서 응축을 수반하는 초음속 유동의 미소진폭 파형벽에 의한 Prandtl-Meyer 팽창)

  • 권순범;안형준;선우은
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.6
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    • pp.1582-1589
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    • 1994
  • The characteristics Prandt1-Meyer expansion of supersonic flow with condensation through a wavy wall in a channel are investigated by experiment and numerical direct marching method of characteristics. In the present study, for the case of moist air flow in the type of indraft supersonic wind tunnel, the dependency of location of formation and reflection of the oblique shock wave generated by the wavy wall and the distribution of flow properties, on the specific humidity and temperature at the entrance of wavy wall and the attack angle of the wavy wall to the main stream is clarified by schlieren photograph, distribution of static pressure and Mach number, and plots of numerical results. Also, we confirm that the wavy wall plays an important key role in the formation of oblique shock wave, and that the effect of condensation on the flow field appears apparently.

Reduced Mass Effects on the Ring Inversion Vibration of 1,3-Cyclohexadiene (1,3-Cyclohexadiene의 고리반전 진동운동에 미치는 환산질량 효과)

  • Choo, Jae Bum;Han, Seong Jun
    • Journal of the Korean Chemical Society
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    • v.41 no.3
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    • pp.123-129
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    • 1997
  • In order to consider the reduced mass effects on the out-of-plane ring inversion vibration of 1,3-CHD, the vector-based computer program has been written and the kinetic energy expansion function for the large amplitude ring inversion vibration has been calculated using this program. The structural parameters for the calculations have been determined from the ab initio HF/6-31G** calculation. The potential energy function for the out-of-plane ring inversion vibration of 1,3-CHD has been determined from the kinetic energy expansion function and previously reported low-frequency Raman data. The vibrational Hamiltonian calculation including kinetic energy expansion function made it possible to determine the more reliable out-of-plane potential energy function for the ring inversion of 1,3-CHD.

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The Starting Behaviour of a Supersonic Ejector Equipped with a Converging-Diverging Diffuser (축소 팽창 디퓨저가 장착된 초음속 이젝터의 시동 특성)

  • Park GeunHong;Kim SeHoon;Jin JungKun;Kwon SeJin
    • Journal of the Korean Society of Propulsion Engineers
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    • v.9 no.2
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    • pp.70-77
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    • 2005
  • An axisymmetric supersonic ejector equipped with a converging-diverging diffuser was built and pressure at various locations along the ejector-diffuser system was recorded with emphasis on the supersonic starting of the secondary flow. In order to find the effects of the opening size of the secondary flow, a number of openings were used with a constant primary pressure. Supersonic starting was possible only for d/D, the ratio of the opening diameter and the diffuser throat diameter, less than 0.306. for larger values of d/D, the ejection begins at subsonic secondary flow condition. With the closure of the opening, the primary flow brings the normal shock downstream of the converging-diverging diffuser And the starting of the ejector continues even after the closure was removed.

A Study of Interpretation of Separation Behavior in Gas Expansion Separation(GES) Bolt (가스팽창분리형 볼트 분리거동 해석 연구)

  • Lee Young Jo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.9 no.1
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    • pp.27-34
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    • 2005
  • The present work has been developed the study of interpretation of separation behavior in gas expansion separation(GES) bolt which has the separation characteristics without fragmentation and minimum pyre-shock during the operation of the explosive bolt. In order to obtain the performance of minimum pyre-shock, the present work used non-compressive material instead of separation explosives. The use of the interpretation processor could be extensively helped to design the shape and the amount of explosives in the explosive bolt having complex geometry, and to analyse the separation behavior during the operation. It is also proved that the GES bolt is the most suitable the separation system necessary to minimum pyre-shock and non fragmentation compare with others.

An Improved AE Source Location by Wavelet Transform De-noising Technique (웨이블릿 변환 노이즈 제거에 의한 AE 위치표정)

  • Lee, Kyung-Joo;Kwon, Oh-Yang;Joo, Young-Chan
    • Journal of the Korean Society for Nondestructive Testing
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    • v.20 no.6
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    • pp.490-500
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    • 2000
  • A new technique for the source location of acoustic emission (AE) in plates whose thichness are close to or thinner than the wavelength has been studied by introducing wavelet transform de-noising technique. The detected AE signals were pre-processed using wavelet transform to be decomposed into the low-frequency, high-amplitude flexural components and the high-frequency, low-amplitude extensional components. If the wavelet transform de-noising was employed, we could successfully filter out the extensional wave component, one of the critical errors of source location in plates by arrival time difference method. The accuracy of source location appeared to be significantly improved and independent of the setting of gain and threshold, plate thickness, sensor-to-sensor distance, and the relative position of source to sensors. Since the method utilizes the flexural component of relatively high amplitude, it could be applied to very large, thin-walled structures in practice.

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Numerical Simulation of the Effect of Finite Diaphragm Rupture Process on Micro Shock Tube Flows (Micro shock tube 유동에 대한 유한 격막 파막과정의 영향에 관한 수치 해석적 연구)

  • Arun Kumar, R.;Kim, Heuy Dong
    • Journal of the Korean Society of Propulsion Engineers
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    • v.17 no.3
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    • pp.37-46
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    • 2013
  • Recent years have witnessed the use of micro shock tube in various engineering applications like micro combustion, micro propulsion, particle delivery systems etc. The flow characteristics occurring in the micro shock tube shows a considerable deviation from that of well established conventional macro shock tube due to very low Reynolds number and high Knudsen number effects. Also the diaphragm rupture process, which is considered to be instantaneous process in many of the conventional shock tubes, will be crucial for micro shock tubes in determining the near diaphragm flow field and shock formation. In the present study, an axi-symmetric CFD method has been applied to simulate the micro shock tube, with Maxwell's slip velocity and temperature jump boundary conditions. The effects of finite diaphragm rupture process on the flow field and the shock formation was investigated, in detail. The results show that the shock strength attenuates rapidly as it propagates through micro shock tubes.

An Experimental Study of Shock Wave Effects on the Model Scramjet Combustor (모델 스크램제트 연소기에서 충격파 영향에 대한 실험적 연구)

  • 허환일
    • Journal of the Korean Society of Propulsion Engineers
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    • v.3 no.1
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    • pp.65-71
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    • 1999
  • An experimental study was carried out in order to investigate the effect of shock waves on the supersonic hydrogen-air jet flames stabilized in the Mach 2.5 model scramjet combustor. This experiment was the first reacting flow experiment interacting with shock waves. Two identical $10^{\cire}$ wedges were mounted on the diverging sidewalls of the combustor in order to produce oblique shock waves that interacted with the flame. Schlieren visualization pictures, wall static pressures, and combustion efficiency at two different air stagnation temperatures were measured and compared to corresponding flames without shock wave-flame interaction. It was observed that shock waves significantly altered the shape of supersonic jet flames, but had different effects on combustion efficiency depending on air temperatures. At the higher air stagnation temperature and higher fuel flow rates, combustion of efficiency showed a better result.

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