• 한국항공우주학회지
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• 제31권5호
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• pp.1-9
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• 2003

본 연구에서는 비정렬격자계를 사용하여 덮개 꼬리 로터의 제자리 비행에 대한 압축성, 비정성 유동을 해석하였다. 유동계산을 위한 수치적 기법으로는 셀 중심에 기초한 유한체적법과 내재적인 시간적분법을 사용하였다. 계산은 로터의 한 블레이드에 대해 수행되었으며, 블레이드와 블레이드 사이에는 주기적 경계조건을 설정하였다. 덮개가 없는 로터 형상에 대한 성능은 실험 결과와 잘 일치함을 보였다. 덮개를 포함하는 로터 형상에 대한 계산은 비교된 실험 형상의 불확실성을 고려하여 추력이 일치하는 피치각을 가지는 경우에 대해 수행하였으며, 자세한 유동은 실험결과와 잘 일치함을 확인할 수 있었다. 그 결과로부터 본 방법이 블레이드 끝단간극을 포함하는 복잡한 3차원 덮개 꼬리 로터 형상 해석에 매우 유용하게 사용될 수 있음을 알 수 있었다.

• 대한조선학회논문집
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• 제49권1호
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• pp.26-32
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• 2012

The 3-D unsteady viscous flow around an impulsively started rotating marine propeller is simulated using VIC(Vortex-In-Cell) method which is adequate to analyze the strong vortical flow around complicatedly-shaped body. The computational procedure is governed by the vorticity transport equation in Lagrangian form. In order to solve the equation, a regular grid which is independent to the shape of a body is introduced and each term of the equation is evaluated numerically on the grid by applying immersed boundary concept. In this paper, the overall algorithm including the formulation of governing equations and boundary conditions is described and some computational results are presented with discussing their physical validity.

• 대한기계학회논문집B
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• 제29권9호
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• pp.1049-1056
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• 2005

A conservative pressure-based finite-volume numerical method has been developed for computing flow and heat transfer by using an unstructured grid system. The method admits arbitrary convex polyhedra. Care is taken in the discretization and solution procedures to avoid formulations that are cell-shape-specific. A collocated variable arrangement formulation is developed, i.e. all dependent variables such as pressure and velocity are stored at cell centers. Gradients required for the evaluation of diffusion fluxes and for second-order-accurate convective operators are found by a novel second-order accurate spatial discretization. Momentum interpolation is used to prevent pressure checkerboarding and the SIMPLE algorithm is used for pressure-velocity coupling. The resulting set of coupled nonlinear algebraic equations is solved by employing a segregated approach, leading to a decoupled set of linear algebraic equations fer each dependent variable, with a sparse diagonally dominant coefficient matrix. These equations are solved by an iterative preconditioned conjugate gradient solver which retains the sparsity of the coefficient matrix, thus achieving a very efficient use of computer resources.

• 대한기계학회논문집B
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• 제27권5호
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• pp.635-643
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• 2003

Parametric study for the analysis of performance characteristics of a planar -type solid oxide fuel cell(SOFC) using computational flow analysis is conducted. A planar -type SOFC, which is composed by two gas channels (fuel and ai.) and one set of anode-electrolyte-cathode assembly, is modeled as a two -dimensional isothermal case. Results of computational analysis of flow field including distributions of mass fractions in gas channels are used to the performance analysis of the fuel cell. Flow analysis makes it possible to consider current density distributions along the length of the cell in the process of performance analysis of the SOFC. As results of parametric study, it is found that the mole fraction of fuel at the inlet of fuel channel, operating pressure and temperature are closely related to the performance characteristics of SOFC.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.835-840
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• 2009

In this paper, confined multiple slot jet impingement with exhaust ports is investigated numerically. A flow cell, defined as volume sectioned by the impingement and confinement surfaces and the centerlines of adjacent nozzle and exhaust port, is chosen for computational domain. The effects of Reynolds number and geometrical parameters on the heat transfer performance and the flow characteristics are studied. For turbulence, the Abe-Kondoh-Nagano version of the low-Reynolds k-$\varepsilon$ model is employed. The results showed that the local Nusselt number distribution is shifted down and show poor heat transfer performance for small Reynolds number and small ratio of the lateral and axial length of flow cell. The rest of range, except the range of the shift phenomenon, can be classified into three groups by heat transfer characteristics.

• 한국전산유체공학회지
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• 제4권2호
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• pp.57-66
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• 1999

Numerical Analysis has been done for the supersonic off-design jet flow due to the pressure difference between the jet and the ambient fluid. The difference of pressure generates an oblique shock or an expansion wave at the nozzle exit. The waves reflect repeatedly on the center axis and the sonic surface in the shear layer. The pressure difference is resolved across these reflected waves. In this paper, the axi-symmetric Navier-Stokes equation has been used with the κ-ε turbulence model. The second order TVD scheme with flux limiters, based on the flux vector split with the smooth eigenvalue split, has been used to capture internal shocks and other discontinuities. Numerical calculations have been done to analyze the off-design jet flow due to the pressure difference. The variation of pressure along the flow axis is compared with an experimental result and other numerical result. The characteristics of the interaction between the shock cell and the turbulence mixing layer have been analyzed.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.518-522
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• 2011

Cartesian grid system has mainly been used in the casting simulation even though it does not nicely represent sloped and curved surfaces. These distorted boundaries cause several problems. A special treatment is necessary to clear these problems. A cut cell method on Cartesian grids has been developed to simulate three-dimensional mold filling Cut cells at a cast-mold interface are generated on Cartesian grids. Governing equations were computed using volume and areas of cast at cut cells. In this paper, we propose a new method that can consider the cutting cells which are cut by casting and mold based on the patial cell treatment (PCT). This method provides a better representation of geometry surface and will be used in the computation of velocities that are defined on the cell boundaries in the Cartesian gird system. Various test examples for several casting process were computed and validated. The analysis results of more accurate fluid flow pattern and less momentum loss owing to the stepped boundaries in the Cartesian grid system were confirmed. We can know the momentum energy at the cut cell is conserved by using the cut cell method. By using the cut cell method. performance of computation gets better because of reducing the whole number of meshes.

• 대한기계학회논문집B
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• 제30권10호
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• pp.966-972
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• 2006

A numerical simulation is performed fur developing turbulent flow in a strongly curved 180 deg pipe and its downstream tangent by a new solution code(PowerCFD) which adopts an unstructured cell-centered method. The governing equations are discretized as the full elliptic from of the equations of motion. Three typical two-equation turbulence models of low-Reynolds-number form are used to approximate the turbulent stress field. Solutions fur both streamwise and circumferential velocity components are compared with the experimental data by Azzola et at.(1986). The ${\kappa}-{\omega}$ model by Wilcox(1988) is found to give better prediction performance than the other two. Predicted secondary velocities and streamwise velocity component contours at sequential longitudinal stations are also presented in order to enable a detailed description of the complete flow. It is also found that, in the bend both mean streamwise and secondary velocities never achieve a fully-developed state and the code is capable of producing very well the complex nature of steady flow in a strongly curved pipe.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.329-334
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• 2007

초음속 제트 마하수 1.07부터 1.2 범위에서 축대칭 제트 스크리치 톤을 해석하였다. 축대칭 모드는 낮은 마하수 축대칭 제트의 지배적인 스크리치 톤 모드이다. 난류 해석을 위해 수정된 Spalart-Allmaras 모델을 RANS (Reynolds-averaged Navier-Stokes) 방정식에 사용하였다. 스크리치 톤 해석에서 중요한 음파의 전파, shock-cell 구조, shock-cell의 비정상 거동 및 거대한 불안정 파를 정확히 계산하기 위해 비반사 특성 경계조건과 연계한 고차정확도의 ENO 기법을 사용하였다. 수치해석결과는 다른 연구자들의 실험 결과와 잘 일치하였으며, 따라서 본 연구에 사용된 수치 기법들이 초음속 제트 유동 구조 및 소음연구에 유용함을 확인하였다.

• 에너지공학
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• 제20권1호
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• pp.44-53
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• 2011

본 논문에서는 마주보는 두 벽면들이 서로 다른 온도로 유지되는 2차원 사각형 공간 내 공기의 층류 자연대류를 수치해석 방법을 사용하여 $10^6$의 Rayleigh 수까지 조사하였다. 사각공간의 폭과 높이의 비가 1, 2, 4인 경우와 $0^{\circ}{\leq}{\theta}{\leq}90^{\circ}$의 경사각도 범위에서 계산을 수행하였다. $10^3{\leq}Ra{\leq}10^6$의 범위에서 공간의 경사각도가 유동 구조와 열전달에 미치는 영향을 각 종횡비에 대하여 조사하였다. 작은 종횡비의 경우에는 공간 구석에서 발달되는 2차 유동 셀들이 총괄 열전달의 감소를 초래하는 것으로 나타났으며, 큰 종횡비의 경우에는 3개의 유동 셀이 1개로 전이되는 과정에서 스텝모양과 비슷한 열전달의 급 감소가 일어났다. 수직의 경우인 ${\theta}=90^{\circ}$에 대해서 새로운 평균 Nusselt 수 상관식이 제공되었다.