• Journal of the korean Society of Automotive Engineers
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• v.14 no.3
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• pp.115-125
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• 1992

혼합 대류 이상 유동 시스템에 부유된 슈트와 미분탄과 같은 고흡수, 방사하는 입자의 열확산적 입자이동에 대한 복사 및 부력효과를 수치적으로 검토하였다. 기체 및 입자유동의 지배방정식 들은 Euler 관점의 two-fluid model의 근간에서 수행되었으며, 에너지 보존식의 비선형 복사 생 성항은 P-1 근사방법에 의해 계산되었다. 혼합 대류 유동에서의 입자의 열확산 현상은 복사 열 전달과 커플링되며, 복사효과의 증가는 부력효과를 상대적으로 감소시켜 부력효과에 의한 입자 부착율을 완화시켰다. 복사효과가 무시될 때 Grashof 수의 증가에 따라 입자의 확산효과는 감 소되었으며, 복사효과가 함께 작용될 때 입자 부착율은 증가됨을 보였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.04a
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• pp.17-17
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• 2000

이젝터-디퓨저 시스템은 고압의 기체를 노즐로 팽창시켜서 얻은 대량의 운동에너지를 이용하여 낮은 에너지를 가지는 주변의 기체를 외부로 배출시키는데 이용되는 유체 역학적 펌프이다. 이젝터-디퓨저 시스템은 작동부가 없고 구조가 단순하여 설치/보수 및 시스템 전체의 경량화에 많은 이점이 있으므로 그 활용도가 증대하고 있는 추세이다. 그러나 이젝터-디퓨저를 지나는 초음속 유동은 복잡한 충격파 및 난류현상들로 인하여 그 물리적 특성들이 명확히 알려지지 않았다. 특히 이러한 제현상들의 간섭과 전단층의 불안정성 때문에 발생하는 비정상성은 1차 유동과 2차 유동의 혼합작용에 영향을 미쳐, 결국 시스템 전체의 배기성능을 저하시킬 뿐만 아니라, 소음과 진동을 발생시켜 시스템의 안정적인 운전을 방해한다.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1998.05a
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• pp.27-30
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• 1998

지난 수십 년간 순환유동층과 riser 반응기에 관한 연구는 상당한 진전을 이뤄왔다. 비록, 순환유동층(riser)반응기가 전형적인 유동층에 비해 여러 가지 장점 -높은 기-고의 접촉효율, 높은 기체와 고체의 처리량, 기상과 고상의 낮은 축방향 분산, 높은 turndown ratio, 점결성 입자의 처리-을 가지고 있으나, 불균일한 기-고의 흐름에 의한 고체의 역혼합(back-mixing)으로, 기체와 고체의 반경방향의 분리를 일으켜 두상간의 접촉을 감소시켜 생성물의 균일성과 선택도를 감소시킨다. 이러한 riser 반응기의 단점을 보완하기 위해 최근에는 기-고의 하향흐름을 갖는 downer(downflow) 반응기에 대한 관심이 증가하고 있다. (중략)

• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.901-906
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• 1998

Gas and liquid flow characteristics were investigated in an internal circulation airlift reactor using a single nozzle for a gas distributor. In three reactors with different diameters of the downcomer and heights of the riser, the gas holdup in the individual flow zone and the impulseresponse curve of tracer for an air-water system were measured for various gas velocities and reactor heights. Experimental results showed that the flow behavior of bubbles in the riser was the slug flow due to strong coalescences of bubbles and that the bubble flow pattern in the downcomer was the transition bubble flow for the smaller diameter of the downcomer, however, it was the homogeneous bubble flow for the larger one. And mean gas holdups in the individual flow zone and the reactor were greatly increased with decreasing the diameter of the downcomer for the equal ratio of height of the top section to that of the riser. Also, the mixing time was much effected by the height of the top section of reactor and for the equal ratio of height of top section to that of the riser, it was increased with increasing the diameter of the downcomer and the height of the riser. Flow characteristics of liquid were mainly varied with the bubble flow pattern in the downcomer and the size of the top section of reactor. And circulation velocities of liquid in the riser were increased with increasing gas velocities and the size of the top section of reactor, and for the equal ratio of height of top section to that of the riser, they were increased with increasing the diameter of the downcomer and the height of the riser.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.1
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• pp.9-17
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• 2015

The basic flow configuration is composed of a plane, double shear layer where relatively thin mid gas layer is sandwiched between air and fuel stream. The present study describes numerical investigations concerning the combustion enhancement according to a variation of mid layer thickness. In this case, the effect of heat release in turbulent mixing layers is important. For the numerical solution, a fully conservative unsteady $2^{nd}$ order time accurate sub-iteration method and $2^{nd}$ order TVD scheme are used with the finite volume method including k-${\omega}$ SST model. The results consists of three categories; single shear layer consists of fuel and air, inert gas sandwiched between fuel and air, cold fuel gas sandwiched between fuel and air. The numerical calculations has been carried out in case of 1, 2, 4 mm of mid layer thickness. The height of total gas stream is 4 cm. The combustion region is broadened in case of inert gas layer of 2, 4 mm thickness and cold fuel layer of 4 mm thickness compared with single shear layer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.7
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• pp.675-682
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• 2013

To verify the effect of inner- and outer-stage gas jets, a shear coaxial injector was designed to analyze the axial velocity profile and breakup phenomenon with an increase in the measurement distance. When the measurement position was increased to Z/d=100, the axial flow showed a fully developed shape due to the momentum transfer, aerodynamic drag effect, and viscous mixing. An inner gas injection, which induces a higher momentum flux ratio near the nozzle, produces the greater shear force on atomization than an outer gas injection. Inner- and Outer-stage gas injection do not affect the mixing between the inner and outer gas flow below Z/d=5. The experiment results showed that the main effect of liquid jet breakup was governed by the gas jet of an inner stage. As the nozzle exit of the outer-stage was located far from the liquid column, shear force and turbulence breaking up of the liquid jets do not fully affect the liquid column. In the case of an inner-stage gas injection momentum flux ratio within 0.84, with the increase in the outer gas momentum flux ratio, the SMD decreases. However, at an inner-stage gas jet momentum flux ratio over 1.38, the SMD shows the similar distribution.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.17-17
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• 1997

극초음속 여객기와 군사용 항공기에 대한 수요가 증가함에 따라서 새로운 개념의 다양한 추진기관이 연구가 진행되고 개발되어 왔다. 초음속 항공기의 속도 영역은 마하 10-20 정도가 되는데 이 속도 한계를 극복하기 위하여 초음속 연소 램제트 엔진(SCRamjet; Supersonic Combustion Ramjet)이 제안되었다. 스크램 제트를 개발하기 위해서는 연료와 산화제의 혼합 효율 문제, 화염의 안정화 문제, 벽면의 냉각에 관한 문제 등 몇 가지 기본적인 문제들을 해결해야 한다. Univ of Michigan에서 실험한 연소기를 모델로 본 연구에서는 연료와 공기의 혼합에 관한 수치 연구를 수행하였다. 다원 혼합기체에 관한 축대칭 Navier-Stokes 방정식을 지배 방정식을 이용하였고 비평형 화학반응식을 고려하였다. 공간 차분에는 유한 체적법을 이용하였다. 대류 플럭스 항은 Roe의 Upwind FDS 기법을 사용하여 차분하였고 점성항에는 중심 차분법을 이용하였다. 시간 적분법으로는 근사 자코비안과 LU분할 기법을 이용한 완전 내재적 방법이 쓰였다. 난류 모델로는 Mentor에 의해 제안된 2 방정식 k-$\varepsilon$/k-$\omega$ 혼합모델을 사용하였다. 유동장이 실험에서의 찍은 사진과 유사한 모습의 충격파 간섭을 수치 모사하였고 수소가 확산되는 모습과 함께 노즐 lip 주위의 재순환 영역에 대해서 살펴볼 수 있었다.

• Nuclear Engineering and Technology
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• v.22 no.2
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• pp.116-127
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• 1990

The fission gas release model used In the SPEAR-BETA fuel performance code was modified by use of effective thermal conductivity for cracked fuel and by laking Into account axial fission-gas mixing between the fuel-clad gap and the plenum. With use of this modified model the fission gas release was analyzed under various power ramping conditions of P$_{max}$ and $\Delta$.fP. Effective fuel thermal conductivity that accounts for the effect of fuel tracking was used in calculation of the fuel temperature distribution and the Internal gas pressure under power ramping conditions. Mixing and dilution effects due to axial gas flow were also considered in computing the width and the thermal conductivity of the gap. The effect of axial gas flow w3s solved by the Crank-Nicholson method. The finite difference method was used to save running time in the calculation. The present modified fission-gas release model was validated by comparing its predicted results with experimental data from various lamping tests In the literature and calculated results with use of the models used In the SPEAR-BETA and FEMAXI-IV codes. Results obtained with use of the present modified model showed better agreement with experimental data reported in the literature than those results with use of the latter codes. The fuel centerline temperature calculated with introduction of effective thermal conductivity for centerline temperature calculated with Introduction of effective thermal conductivity for cracked fuel was 200 higher fission gas release predicted with use of the modified model was nearly 6% larger on the average than that calculated by use of the unmodified model used in the SPEAR-BETA code.e SPEAR-BETA code.e.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.1
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• pp.1-16
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• 2009

In this paper, we introduce two-phase versions of RoeM and AUSMPW+ schemes. Both schemes are originally developed for the gas dynamic problems, and have shown superior accuracy, efficiency and robustness. A new shock discontinuity sensing term is derived from the mixture equation of state, which is commonly used in the RoeM and AUSMPW+ schemes for the stable numerical flux calculation. The developed two-phase versions of the schemes are applied to several liquid-gas, large property discrepancy two-phase test problems, including several shock stability test problems. The results show that both schemes maintain the merits exhibited in gas dynamic problems even in two-phase flows.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.3
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• pp.327-334
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• 1985

본 연구에서는 개선된 Sung과 Chung의 모델을 이용하여 Choi와 Chung이 취급 한 직관에서의 압력강하의 속도분포를 재해석하고 그 결과를 Choi와 Chung의 결과와 비교함으로써 개선된 Sung과 Chung의 모델이 좀더 정확한 해를 주는지의 여부를 고찰 하기로 한다.