• 한국응용약물학회:학술대회논문집
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• 한국응용약물학회 1994년도 춘계학술대회 and 제3회 신약개발 연구발표회
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• pp.342-342
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• 1994

(1) 바셀린은 30 $^{\circ}C$ 이하에서는 항복치를 갖는 의소성 유동거동을 나타내며 이때의 유동특성은 Herschel-Bulkley의 유동모델과 일치한다. (2) 30-50 $^{\circ}C$ 범위에서는 Bingham 모델에 따른 이상 소성 유동 거동을 나타낸다. (3) 50 $^{\circ}C$ 이상의 고온에서는 항복치를 갖지 않는 순수한 Newton 점성유체로 간주할 수 있다. (4) 바셀린의 유동곡선은 전단속도의 단계적 증감에 따라 비가역적인 히스테리시스 루프를 그리나 루프의 면적은 온도 증가에 따라 감소한다. (5) 큰 전단속도로부터 급격히 낮은 전단속도를 부가하면 응력의 평형치에 도달할 때까지 상당한 시간을 필요로 한다. (6) 40 $^{\circ}C$ 이상 온도에서의 유동거동은 시간에 무관하다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.434-440
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• 2011

Oscillating airfoil haw been challenged for the dynamic stalls of airfoil am wind turbines at high angle of attach. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance am safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed for the oscillating airfoil at high angle of attack around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.2 and Reynolds number of $1.2{\times}10^4$. The lift, drag, pressure distribution, etc. are analyzed according to the pitching oscillation. Unsteady velocity field, periodic vortex shedding, the unsteady pressure distribution, and the acoustic fields are analyzed. The effects of these unsteady characteristics in the aerodynamic coefficients are analyzed.

• 한국전산유체공학회지
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• 제15권2호
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• pp.86-94
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• 2010

A thermal-hydraulic code, named CUPID, has been developed for the analysis of transient two-phase flows in nuclear reactor components. A two-fluid three-field model was used for steam-water two-phase flows. To obtain numerical solutions, the finite volume method was applied over unstructured cell-centered meshes. In steam-water two-phase flows, a phase change, i.e., evaporation or condensation, results in a great change in the flow field because of substantial density difference between liquid and vapor phases. Thus, two-phase flows are very sensitive to the local pressure distribution that determines the phase change. This in turn puts emphasis on the accurate evaluation of local pressure gradient. This paper presents a new reconstruction method to evaluate the pressure gradient at cell centers on unstructured meshes. The results of the new scheme for a simple test function, a gravity-driven cavity, and a wall boiling two-phase flow are compared with those of the previous schemes in the CUPID code.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.49-55
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• 2004

This paper addresses a numerical simulation of the flow and heat transfer in a simplified model of helically coiled tube steam generator using a general purpose computational fluid dynamic analysis computer code. The steam generator model is comprised of a cylindrical shell and helically coiled tubes. A cold feed water entered the tubes is heated up, evaporates. and finally become a superheated steam with a large amount of heat transferred continuously from the hot compressed water at higher pressure flowing counter-currently through the shell side. For the calculation of tube side two-phase flow field formed by boiling, inhomogeneous two-fluid model is used. Both the internal and external turbulent flows are simulated using the standard k-e model. The conjugate heat transfer analysis method is employed to calculate the conduction in the tube wall with finite thickness and the convections in the internal and external fluids simultaneously so as to match the fluid-wall-fluid interface conditions properly. The numerical calculations are peformed for helically coiled tubes of steam generator at an integral type pressurized water reactor under normal operation. The effects of tube-side inlet flow velocity are discussed in details. The results of present numerical simulation are considered to be physically plausible based on the data and knowledge from previous experimental and numerical studies where available.

• 한국전산유체공학회지
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• 제14권4호
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• pp.13-22
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• 2009

A two-phase (gas and liquid) flow analysis solver, named CUPID, has been developed for a realistic simulation of transient two-phase flows in light water nuclear reactor components. In the CUPID solver, a two-fluid three-field model is adopted and the governing equations are solved on unstructured grids for flow analyses in complicated geometries. For the numerical solution scheme, the semi-implicit method of the RELAP5 code, which has been proved to be very stable and accurate for most practical applications of nuclear thermal hydraulics, was used with some modifications for an application to unstructured non-staggered grids. This paper is concerned with the effects of interpolation schemes on the simulation of two-phase flows. In order to stabilize a numerical solution and assure a high numerical accuracy, the second-order upwind scheme is implemented into the CUPID code in the present paper. Some numerical tests have been performed with the implemented scheme and the comparison results between the second-order and first-order upwind schemes are introduced in the present paper. The comparison results among the two interpolation schemes and either the exact solutions or the mesh convergence studies showed the reduced numerical diffusion with the second-order scheme.

• 한국유체기계학회 논문집
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• 제13권4호
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• pp.31-36
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• 2010

Free energy based lattice Boltzmann method (LBM) has been used to simulate the rising bubble flows with large density ratio. LBM with compact discretization is able to reduce the spurious current of the static bubble test and be satisfied with the Laplace law. The terminal rise velocity and shape of the bubbles are dependent on Eotvos number, Morton number and Reynolds number. For single bubble flows, simulations are executed for various Eotvos number, Morton number and Reynolds number, and the results are agreed well with the experiments. For multiple bubbles, the bubble flow characteristics are related by the vortex pattern of the leading bubble. The coalescence of the bubbles are simulated successfully and the subsequent results are presented. The present method is validated for static, dynamic bubble test cases and compared to the numerical, experimental results.

• 한국전산유체공학회지
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• 제19권3호
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• pp.91-97
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• 2014

A high resolution numerical method aimed at solving cavitating flow was proposed and applied to gas-liquid two-phase shock tube problem with arbitrary void fraction. The present method with compressibility effects employs a finite-difference 4th-order Runge-Kutta method and Roe's flux difference splitting approximation with the MUSCL TVD scheme. The Jacobian matrix from the inviscid flux of constitute equation is diagonalized analytically and the speed of sound for the two-phase media is derived by eigenvalues. So that the present method is appropriate for the extension of high order upwind schemes based on the characteristic theory. By this method, a Riemann problem for Euler equations of one dimensional shock tube was computed. Numerical results of high speed flow phenomena such as detailed observations of shock and expansion wave propagations through the gas-liquid two-phase media and some data related to computational efficiency are made. Comparisons of predicted results and solutions at isothermal condition are provided and discussed.

• 대한기계학회논문집B
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• 제38권1호
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• pp.9-16
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• 2014

본 논문은 경사진 원형관에서 표면장력과 중력으로 구동되는 비뉴턴 유체(멱법칙 모델)의 유동 및 변위를 이론적으로 연구한 것이다. 그리고 표면장력에 의하여 연속적으로 원형관 내로 유입되는 비뉴턴 유체의 변위를 기술하기 위한 지배방정식을 처음으로 개발하였다. 뉴턴의 운동방정식으로부터 유도된 식은 2계 비선형이며 비제차인 형태의 상미분 방정식이다. 지배방정식의 해를 수평관에서 변위를 시간의 함수로 기술한 식 및 실험과 비교한 결과 정량적으로 동일한 일치를 보였다. 여기에 더하여 정상상태인 힘의 균형식의 결과에 대해서도 정확한 일치로 나타남을 확인할 수 있었다.

• 한국유체기계학회 논문집
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• 제14권3호
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• pp.10-17
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• 2011

Free energy based lattice Boltzmann method (LBM) has been used to simulate the contact angle and the bubble necking with large density ratio. LBM with the proper contact angle model is able to reduce the spurious currents and eliminate the singularity in the contact lines. The numerical results of the contact angles are satisfied with the Youngs law. For bubble necking flows, simulations are executed for various viscosities and contact angles. The phenomena of the bubble necking are simulated successfully and the subsequent results are presented. The present method is also applicable to the nucleate boiling flows.

• 대한기계학회논문집B
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• 제41권11호
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• pp.709-717
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• 2017

연구는 직렬 2단 Weis-Fogh형 수차모델을 제안하고, 이 수차모델의 유체역학적 특성을 개선 와법으로 수치계산한 것이다. 기본조건 및 각 날개의 움직임은 이전에 저자가 제안한 단단 수차모델에서와 같게 했다. 두 날개(NACA0010 airfoils) 및 양쪽 수로벽은 소스 및 볼텍스 판넬로 근사하였고, 자유볼텍스는 각 물체 표면 전체에서 도입하였다. 계산변수로는 앞날개와 뒷날개의 날개 축 사이의 거리 및 두 날개 운동의 위상차 즉 동위상과 역위상으로 했다. 각 경우에 대해 비정상 유동장 및 압력장 그리고 두 날개에 작용하는 힘의 계수 및 효율을 계산하였고, 이 수차모델의 유체역학적 특성을 논의하였다.