• 에너지공학
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• 제22권4호
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• pp.399-405
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• 2013

엔진 실린더 내부의 난류유동 특성은 내연기관의 열효율을 결정하는 매우 중요한 역할을 한다. 실린더 내 난류유동은 복잡한 3차원 유동으로 유동특성에 대한 자세한 정보는 엔진설계의 최적화를 위해 필수적이다. 균일 예혼합 압축착화(HCCI) 엔진은 가솔린과 디젤엔진 사이의 하이브리드 연소개념이다. 실린더 내 기체의 난류유동은 운동량과 열의 혼합 및 전달률을 증가시키므로 벽면에서의 열전달에 관여하여 HCCI 연소 과정에 중요한 영향을 미치게 된다. 본 연구에서는 연소실 형상에 따른 연소실 내의 기체 난류유동을 LES 모델을 사용한 전산수치해석을 통해 분석하여 HCCI 엔진 연소과정에 미치는 영향을 확인하였고 연구결과는 HCCI 엔진에서 연소실 형상에 따른 연소 특성과 엔진 성능을 개선하기 위한 기본적인 지침에 활용될 수 있다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제21회 추계학술대회 논문집
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• pp.238-241
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• 2003

터보펌프식 기체 공급계의 액체산소 탱크는 저압이 유지됨에 따라 탱크 내에서 추진제의 기화가 활발히 이루어지게 되며, 이러한 경향은 가압 기체의 온도가 높아짐에 따라 커지게 된다. 가압헬륨의 충진량을 결정하기 위해서는 이에 대한 정밀한 해석이 필요하다. 본 연구에서는 탱크내의 유동현상을 이상유동(two phase flow) 형태로 모델링 하여 탱크 내에서의 액체산소의 증발현상에 대하여 고찰하고 가압기체 온도 및 표면 열전달 계수에 따른 필요 헬륨 가스량을 예측한다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.227-230
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• 2006

The method of mass flow rate measurement using a critical nozzle is well established in the flow satisfying ideal gas law. However, in the case of measuring high-pressure gas flow, the current method shows invalid discharge coefficient because the flow does not follow ideal gas law. Therefore an appropriate equation of state considering real gas effects should be applied into the method. The present computational study has been performed to give an understanding of the physics of a critical nozzle flow for high-pressure hydrogen gas and find a way for the exact mass flow prediction. The two-dimensional, axisymmetric, compressible Navier-Stokes equations are computed using a fully implicit finite volume method. The real gas effects are considered in the calculation of discharge coefficient as well as in the computation. The computational results are compared with the previous experimental data and predict well the measured mass flow rates. It has been found that the discharge coefficient for high-pressure hydrogen gas can be corrected properly adopting the real gas effects.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.187-194
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• 2005

For the analysis of compressible multi-phase and real gas flows, characteristic form of Roe's Riemann solver was derived using real gas equation of state. It was extended to multi component reactive system considering variable specific heat. From this study, it is known that some correction should be made for the use of existing numerical algorithm. 1) Sonic speed and characteristic variable should be corrected with real gas effect. 2) Roe's average was applicable only with the assumption of constant properties. 3) Artificial damping term and characteristic variables should be corrected but their influences may not be significant.

• 한국군사과학기술학회지
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• 제4권2호
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• pp.202-214
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• 2001

In this paper the upwind flux difference splitting Navier-Stokes method has been applied to study quasi one-dimensional nozzle flow and axisymmetric sphere-cone($5^{\circ}$) flow for the perfect gas, the equilibrium and the nonequilibrium chemically reacting hypersonic flow. The effective gamma(${ \tilde{\gamma}}$), enthalpy to internal energy ratio was used to couple chemistry with the fluid mechanics for equilibrium chemically reacting air. The influences of the various altitude(30km, 50km) at Mach number(15.0, 20.0) were investigated. The equilibrium shock position was located farthest downstream when compared with those of perfect gas in a quasi one-dimensional nozzle. The equilibrium shock thickness over the blunt body region was much thinner than that of perfect gas shock.

• 한국대기환경학회:학술대회논문집
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• 한국대기환경학회 2000년도 추계학술대회 논문집
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• pp.263-264
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• 2000

여과포 표면상에 도달하는 입자의 농토를 낮추거나 균일하게 유지시킬 경우, 부착된 입자층 두께의 성장으로 인한 압력손실의 증가율을 줄일 수 있고 이로 인하여 탈진 주기 또한 감소시킬 수 있다. 탈진조작의 저감으로 인하여 여과포의 수명 증대로 여과포의 교체 시기를 연장시킬 수 있으므로 여과포 집진장치의 운전 및 유지 보수비의 저감을 이룰 수 있다. 본 연구에서는 집진용기의 중간부분에 위치한 접선 유입관을 통하여 오염입자를 함유한 기체유동을 유입시킨 후, 원심력과 난류확산에 의하여 집진용기 내벽과 내통(inner tube) 벽면에 부착된 입자는 중력에 의하여 용기 바닥으로 모인 후 바닥면에 설치된 스크래퍼(scraper)를 통하여 분리 처리될 수 있는 새로운 형상의 집진장치를 개발하고자 하였다. (중략)

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.628-633
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• 2003

An analysis on the steady-state has been made of flow of a compressible fluid rapidly-rotating in a pipe. The flow is induced by an small arbitrary azimuthally-varying thermal forcing added on the basic state of rigid body isothermal rotation. The system Ekman number is assumed to be very small value. Analytic solutions have been obtained for axisymmetric and non-axisymmetric types, in which the axisymmetric solution comes from the azimuthally-averaged wall boundary condition and the non-axisymmetric solution from fluctuating wall boundary condition.

• 한국유체기계학회 논문집
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• 제10권5호
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• pp.27-33
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• 2007

Rarefied gas flows through two-dimensional micro channels are studied numerically for the performance optimization of a nanomembrane-based Knudsen compressor. The effects of the wall temperature distributions on the thermal transpiration flow patterns are examined. The flow has a pumping effect, and the mass flow rates through the channel are calculated. The results show that a steady one-way flow is induced for a wide range of the Knudsen number. The DSMC(direct simulation Monte Carlo) method with VHS(variable hard sphere) model and NTC(no time counter) techniques has been applied in this work to obtain numerical solutions. A critical element that drives Knudsen compressor Is the thermal transpiration membrane. The membranes are based on aerosol or machined aerogel. The aerogel is modeled as a single micro flow channel.

• 한국분무공학회지
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• 제24권1호
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• pp.27-34
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• 2019

An experimental study on the spray characteristics of aerated-liquid jets discharged from effervescent injectors to a subsonic crossflow was conducted to investigate effects of a gas to liquid mass ratio (GLR) and a ratio of the orifice length to the diameter (L/d). The present effervescent injectors consist of a plain orifice injector and an aerator. To analyze breakup length and spray trajectory, instantaneous spray images were taken by a high speed camera. As the GLR increased, the spray penetration became higher under the same liquid mass flow rate and the breakup length became shorter due to the bubble expansion or the annular liquid film breakup. To predict the spray trajectory of two-phase flow jets into the crossflow, the homogeneous and the separated flow models were compared.

• 한국분무공학회지
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• 제27권3호
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• pp.144-154
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• 2022

Gas injection is a technique applied to improve throttling in liquid rocket engines and atomization in effervescent injectors. When a gas is injected into a liquid, it creates a two-phase flow inside the injector. The changes (bubbly flow, slug flow, annular flow, etc.) in the two-phase flow affect the injector's spray characteristics. In this study, cold-flow tests were performed by using three injectors with different orifice diameters and four aerators with different gas injection hole diameters. The experiments were done by changing the thrust ratio (liquid mass flow rate ratio) and gas-liquid mass flow rate ratio. Two-phase flow transition, breakup length, and discharge coefficient according to the injector/aerator design and flow conditions were investigated in detail.