• 한국전산유체공학회지
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• 제21권1호
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• pp.110-116
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• 2016

The present study numerically investigated the deformation of the interface of two-phase fluids flow in a blast furnace. To simulate three-dimensional(3D) incompressible viscous two-phase flow in the furnace filled with the air and molten iron, the volume of fluid(VOF) method based on the finite volume method has been utilized. In addition, the porous medium with the porosity has been considered as the bed of the particles such as cokes and char etc. For the comparison, the single phase flow and the two-phase flow without the porosity have been simulated. The two-phase flow without porosity condition revealed the smooth parabolic profile of the free surface near the outlet. However, the free surface under the porosity condition formed the viscous finger when the free surface was close to the outlet. This viscous finger accelerated the velocity of the free surface falling and the outflow velocity of the fluids near the outlet.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3033-3038
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• 2007

In this research, Rayleigh instability of gas-liquid flow in annular pipe is studied in film boiling using viscous potential flow. Viscous potential flow is a kind of approximation of gas-liquid interface considering velocity field as potential including viscosity. A dispersion relation is obtained including the effect of heat and mass transfer and viscosity. New expression for dispersion relation in film boiling and critical wave number is obtained. Viscosity and heat and mass transfer have a stabilizing effect on instability and its effect appears in maximum growth rate and critical wave number. And the existence of marginal stability region is shown.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.57-60
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• 2006

액상의 환경으로 고속의 기체가 분사될 때 기체-액체 표면에서 일어나는 불안정성에 대해 점성전위 유동의 이론을 이용하여 분석하였다. 기체의 속도가 낮을 경우 액상으로 기포로 형성되지만 속도가 증가하면서 기체는 제트의 형태로 변하게 되는데, 천음속 구간에서 제트로 변하게 되는 것으로 알려져 있다. 본 연구에서는 주로 액체 제트를 해석하는데 사용된 점성전위유동이론을 기체 제트의 불안정성 해석에 응용하였다. 천음속 구간에서 기체 제트의 성장률이 변하는 것을 확인하였다. 초음속 구간으로 가면서 성장률이 감소하는 것을 확인하였다. 그리고 이를 레이놀즈수와 같은 무차원수에 대해 기체 제트의 성장률의 변화에 대해 알아보았다.

• 대한기계학회논문집B
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• 제39권1호
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• pp.97-107
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• 2015

2 상 유동장에 놓인 열 교환기 튜브에 작용하는 점성 감쇠비와 압착막 감쇠비를 예측하기 위한 해석 모델이 개발되었다. 열 교환기 튜브에 작용하는 유동유발진동을 해석하기 위하여 감쇠에 대한 정보가 요구된다. 열 교환기 튜브에서 가장 중요한 에너지 소산 기구는 튜브와 지지물과 같은 구조물과 액체 사이의 동적 작용에 연계되어 있다. 본 모델은 1997 년 발표된 근사모델에 근거하고 부가질량계수를 고려하여 개발되었다. 어림적 해석모델은 동심환 내에서 진동하는 내부 실린더에 작용하는 수력학적 힘을 계산하기 위하여 개발되었다. 점성력을 포함한 수동력은 높고 혹은 낮은 진동 레이놀드 수에 따라 개발된 두 가지 모델을 사용하여 각각 계산할 수 있다. 관군과 지지대에서의 상당 직경과 침투깊이는 관군에 작용하는 점성 감쇠력과 지지대에서의 압착막 감쇠력을 각각 계산하는데 매우 중요한 변수이다. 2 상 유동의 기공률을 계산하기 위하여 균질모델이 사용되었다. 본 모델을 검증하기 위하여, 모델의 해석결과는 기존의 이론으로 구한 결과와 비교하였다. 본 모델을 사용하여 점성 감쇠비와 압착막 감쇠비를 어림적으로 구할 수 있음을 보였다.

• 대한기계학회논문집
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• 제14권1호
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• pp.214-224
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• 1990

본 연구에서는 현 저자의 이전의 연구를 확장하여 균일한 열유속을 갖는 2상 기체-고체입자 위 방정식에서 축 방향의 열전달은 반경 방향의 열전달보다 작아 무시 하였으며, 복사 열전달은 기체와 입자 사이의 온도 차이가 적어 무시하였다. 방정식 중 $F_{px}$ 와 $F_{pr}$ 은 2상 사이의 상호작용에 의한 단위부피당 축방향과 반경방향 의 저항력이며, 수직관의 열전달 특성을 부하도와 상대 입자 크기 $d_{p}$/D를 변화시 켜 가면서 조사하는 것이다.다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.291-293
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• 2011

In this paper, the problem of transonic aerodynamic characteristics of a NACA0012 airfoil is numerically investigated in the inviscid gas-droplet two-phase flow with the compressible two-fluid model. In the present study, the airfoil flight in the cloud is simulated by taking account of the viscous drag of the droplets, the heat transfer, the phase change, and the droplet fragmentation The two-fluid equation system is solved by the fractional-step method and the WAF-HIL scheme. The effects of size and volume fraction of the droplets on the flow characteristics of the airfoil in the cloud are elaborated and discussed.

• 한국해양공학회지
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• 제25권2호
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• pp.15-20
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• 2011

This study aimed at validating the adopted numerical methods to solve two-phase flow around a two-dimensional (2D) rectangular floating structure in regular waves. A structure with a draft equal to one half of its height was hinged at the center of gravity and free to roll with waves that had the same period as the natural roll period of a rectangular barge. In order to simulate the 2D incompressible viscous two-phase flow in a wave tank with the rectangular barge, the present study used the volume of fluid (VOF) method based on the finite volume method with a standard turbulence model. In addition, the sliding mesh technique was used to handle the motion of the rectangular barge induced by the fluid-structure interaction. Consequently, the present results for the flow field and roll motion of the structure had good agreement with those of the relevant previous experiment.

• 대한기계학회논문집
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• 제13권6호
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• pp.1301-1309
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• 1989

본 연구의 목적은 Lumley의 저항감소 모델을 사용하여 여러 부하도하에서 부유유동의 유동 특성을 관찰하는 것으로, 특히 저항감소가 일어날 때와 일어나지 않을 때의 유동특성을 알아 보고자 한다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.118-120
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• 2003

The behavior of viscous fingerings caused by an external force is investigated by using a two­phase lattice Boltzmann method. The effects of the modified capillary number, the viscosity contrast, and the modified Darcy-Rayleigh number on the instability of interfaces are found. The calculated wave numbers are in good agreement with the theoretical ones in the range of wave numbers smaller than 10, but the calculated ones tend to become smaller than the theoretical ones in higher wave numbers.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(2)
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• pp.233-240
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• 1996

Analyses of the viscous and end effects on electromagnetic (EM) pumps of annular linear induction type for the sodium coolant circulation in Liquid Metal Fast Breeder Reactors have been carried out based on the MHD laminar flow analysis and the electromagnetic field theory. A one-dimensional MHD analysis for the liquid metal flowing through an annular channel has been performed on the basis of a simplified model of equivalent current sheets instead of three-phase currents in the discrete primary windings. The calculations show that the developed pressure difference resulted from electromagnetic and viscous forces in the liquid metal is expressed in terms of the slip, and that the viscous loss effects are negligible compared with electromagnetic driving forces except in the low-slip region where the pumps operate with very high flow velocities comparable with the synchronous velocity of the electromagnetic fields, which is not applicable to the practical EM pumps. A two-dimensional electromagnetic field analysis based on an equivalent current sheet model has found the vector potentials in closed form by means of the Fourier transform method. The resultant magnetic fields and driving forces exerted on the liquid metal reveal that the end effects due to finiteness of the pump length are formidable. In addition, a two-dimensional numerical analysis for vector potentials has been performed by the SOR iterative method on a realistic EM pump model with discretely-distributed currents in the primary windings. The numerical computations for the distributions of magnetic fields and developed pressure differences along the pump axial length also show considerable end effects at both inlet and outlet ends, especially at high flow velocities. Calculations of each magnetic force contribution indicate that the end effects are originated from the magnetic force caused by the induced current ( u x B ) generated by the liquid metal movement across the magnetic field rather than the one (E) produced by externally applied magnetic fields by three-phase winding currents. It is concluded that since the influences of the end effects in addition to viscous losses are extensive particularly in high-velocity operations of the EM pumps, it is necessary to find ways to suppress them, such as proper selection of the pump parameters and compensation of the end effects.