• 대한기계학회논문집B
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• 제24권12호
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• pp.1555-1569
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• 2000

Numerical simulation of fluid flow with moving free surface has been carried out. For the free surface flow, a VOF(Volume of Fluid)-based algorithm utilizing a fixed grid system has been investigated. In order to reduce numerical smearing at the free surface represented on a fixed grid system, a new free surface tracking algorithm based on the donor-acceptor scheme has been presented. Novel features of the proposed algorithm are characterized as two numerical tools; the orientation vector to represent the free surface orientation in each cell and the baby-cell to determine the fluid volume flux at each cell boundary. The proposed algorithm can be easily implemented in any irregular non-uniform grid systems that are usual in finite element method (FEM). Moreover, the proposed algorithm can be extended and applied to the 3-D free surface flow problem without additional efforts. For computation of unsteady incompressible flow, a finite element approximation based on the explicit fractional step method has been adopted. In addition, the SUPG(streamline upwind/Petrov-Galerkin) method has been implemented to deal with convection dominated flows. Combination of the proposed free surface tracking scheme and explicit fractional step formulation resulted in an efficient solution algorithm. Validity of the present solution algorithm was demonstrated from its application to the broken dam and the solitary wave propagation problems.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.309-313
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• 2004

Prediction of green water loads acting an the bow deck is an essential part for the design of bow structures against the green water impact. Proper technique of the green water simulation is highly required for the prediction of green water loads. In this paper, a new numerical method for green water simulation, which is based an predictor-corrector-upwind finite difference scheme of the 2nd kind, is introduced. Through the comparisons between computed' results and experimental measurements, it is verified that the present numerical tool is adequate as a practical calculation tool for the green water problem.

• 대한기계학회논문집B
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• 제27권10호
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• pp.1457-1463
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• 2003

In this paper, the response surface method using three-dimensional Navier-Stokes analysis to optimize the shape of a multi-blade centrifugal fan, is described. For numerical analysis, Reynolds-averaged Navier-Stokes equations with standard k - c turbulence model are transformed into non-orthogonal curvilinear coordinate system, and are discretized with finite volume approximations. Due to the large number of blades in this centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models for economic calculations. Linear Upwind Differencing Scheme(LUDS) is used to approximate the convection terms in the governing equations. SIMPLEC algorithm is used as a velocity-pressure correction procedure. Design variables, location of cur off, radius of cut off, expansion angle of scroll and width of impeller were selected to optimize the shapes of scroll and blades. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, the efficiency was successfully improved. It was found that the optimization process provides reliable design of this kind of fans with reasonable computing time.

• 대한기계학회논문집B
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• 제20권8호
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• pp.2561-2571
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• 1996

The flow in the turbomachinery is very unsteady due to the stator-rotor interaction. It has been indicated that the stator-rotor interaction has three distinct causes of unsteadiness: that is, the viscous vortex shedding, wake rotor interaction and potential stator-rotor interaction. In this paper, the mechanism of unsteady potential interaction and wake interaction in the stator-rotor stage flow is numerically investigated in two-dimensional view point. The numerical technique used is the upwind scheme of Van Leer's Flux Vector Splitting(FVS) and cubic spline interpolation is applied on zonal interface. Then, the flow field of a compressor stage composed of NACA 65410 is analyzed. Flow fields are found to be simulated reasonably by this method and the sensitivity due to back-pressure variation is more stronger than rotor-velocity variation.

• 한국추진공학회지
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• 제8권3호
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• pp.53-60
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• 2004

노즐과 익렬의 상호작용과 부분입사 효과를 연구하기 위해 노즐과 터빈의 익렬을 같이 계산하였고, 충격파의 구조와 유동의 현상을 밝혀내기 위해 많은 계산을 하였다. 지배방정식은 시간에 관해서는 오일러 음해법으로, 공간에 관해서는 유한체적법을 사용하여 2차의 상류차분법으로 이산화하였으며 $\kappa$-$\varepsilon$ 난류 모델을 사용하였다. 본 논문에서는 익렬의 앞전에서 발생한 충격파와 확장파가 노즐 유동에 영향을 주는 것과 익렬내부의 유동이 노즐에서 발생한 충격파의 영향을 받는 것을 확인하였다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회 논문집
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• pp.414-418
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• 2005

A finite element model is developed for the numerical simulation of bed elevation change in a curved channel. The SU/PG (Streamline-Upwind/Petrov-Galerkin) method is used to solve 2D shallow water equations and the BG (Bubnov-Galerkin) method is used for the Exner equation. For the time derivative terms, the Crank-Nicolson scheme is used. The developed model is a decoupled model in a sense that the bed elevation does not change simultaneously with the flow during the computational time step. The total load formula with is used for the sediment transport model. The slip conditions are described along the lateral boundaries. The effects of gravity force due to geometry change and the secondary flows in a curved channel are considered in the model. For the verification, the model is applied to two laboratory experiments. The first is $140^{\circ}$ bended channel data at Delft Hydraulics Laboratory and the second is $140^{\circ}$ bended channel data at Laboratory of Fluid Mechanics of the Delft University of Technology. The finite element grid is constructed with linear quadrilateral elements. It is found that the computed results are in good agreement with measured data, showing a point bar at the inner bank and a pool at the outer bank.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.425-429
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• 2006

The understanding and prediction of the behavior of flow in open channels are important to the solution of a wide variety of practical flow problems in water resources engineering. Recently, frequent drought has increased the necessity of an effective water resources control and management of river flows for reserving instream flow. The objective of this study is to develop an efficient and accurate finite element model based on Streamline Upwind/Petrov-Galerkin(SU/PG) scheme for analyzing and predicting two dimensional flow features in complex natural rivers. Several tests were performed in developed all elements(4-Node, 6-Node, 8-Node elements) for the purpose of validation and verification of the developed model. The U-shaped channel of flow and natural river of flow were performed for tests. The results were compared with these of laboratory experiments and RMA-2 model. Such results showed that solutions of high order elements were better accurate and improved than those of linear elements. Also, the suggested model displayed reasonable velocity distribution compare to RMA-2 model in meandering domain for application of natural river flow. Accordingly, the developed finite element model is feasible and produces reliable results for simulation of two dimensional natural river flow. Also, One contribution of this study is to present that results can lead to significant gain in analyzing the accurate flow behavior associated with hydraulic structure such as weir and water intake station and flow of chute and pool.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2009년도 학술발표회 초록집
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• pp.822-826
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• 2009

홍수터에 식재된 수목에 의한 운동량 교환은 흐름의 추가적인 흐름저항으로 작용한다. 따라서 수목으로 인한 통수능의 감소로 부분적인 유속 상승이 발생하기도 하지만, 전반적으로 평균유속이 감소하며 수위는 상승하게 된다. 실무적 사용목적으로 홍수터 수목의 저항은 통합 매개변수인 합성조도계수가 사용되고 있으나, 정량적인 조도계수의 추정은 매우 어려운 문제이다. 본 연구에서는 경험적으로 추정되는 비정량적 합성조도 계수의 한계를 극복하고, 실무적으로 사용이 용이하도록 수목에 의한 흐름저항 항을 분리한 1차원 상류이송 음해기법이 개발되었다. 개발된 기법의 평가를 위하여 균일한 단면에서 수행된 수리실험에 적용하였으며, 다양한 유량규모 및 식재조건에서 제안된 기법의 적용성 및 정확성을 확인하였다. 불규칙한 단면형상을 가진 실제 하천의 홍수터에 식재된 수목군의 경우를 가정하여 1/25 정상축척의 수리실험을 실시하였고, 100년 빈도 홍수량에서 수목식재 전후의 실측결과를 개발된 수치기법으로 계산하여 비교하였다. 개발된 기법은 모든 경우에서 사용자의 주관적인 판단 없이 정확하면서 안정적인 해를 제공하였으므로, 흐름의 2차원 효과가 상쇄될 수 있는 광폭의 자연하천에서 수목의 식재기준 분석을 위한 대안으로 사용될 수 있을 것이다.

• 에너지공학
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• 제12권1호
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• pp.29-34
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• 2003

압력파의 일종인 열음향파는 압축성유체를 급속히 가열 또는 냉각하는 경계면 근처에서 유체가 순간적으로 압축 및 팽창하는 경우에 발생하는 현상으로 자연대류가 일어나지 않는 우주공간에서는 매우 중요한 열전달 메커니즘이다. 본 연구에서는 공기로 채워진 공간에서 급속한 가열에 의하여 발생한 열음향파의 전달특성을 수치적인 방법에 의하여 평가하고자 유한체적법을 기반으로 비정상 지배방정식을 이산화하였으며, PISO알고리즘과 2계 상향기법을 적용하여 해석을 수행하였다. 안정적인 수치해는 50 $\times$ 800 개의 셀과 1 $\times$ $10^{-9}$ 시간간격을 적용하여 얻을 수 있었으며, 생성된 열음향파는 유체 속을 통과하면서 점성과 열소산에 의하여 점점 감쇠하여 가는 경향을 보였다. 생성된 압력파는 날카로운 전단과 점점 감소하여 길게 늘어지는 후단부를 갖는 형상을 보였다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
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• pp.42-48
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• 1998

Numerical study is presented for the analysis of three-dimensional incompressible turbulent flows in multiblade centrifugal fan. Reynolds-averaged Navier-Stokes equations with standard k - $\epsilon$ turbulence model are transformed to non-orthogonal curvilinear coordinates, and are discretized with finite volume approximations. Linear Upwind Differencing Scheme(LUDS) is used to approximate the convection terms in the governing equations. SIMPLEC algorithm is used as a velocity-pressure correction procedure. The computational area is divided into three blocks; core, impeller and scroll, which are linked by multi-block method. The flow inside of the fan is regarded as steady flow, and mathematical formula established from the cascade theory and empirical coefficient are employed to simulate tile flow through the impeller. From comparisons between the computational results and the experimental data, the validity of the mathematical formula for the blade forces was examined and good results were obtained qualitatively. Hence, we can get the flow characteristics of multi-blade centrifugal fan and it will be a corner stone of the development of the multiblade centrifugal fan.