• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.148-153
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• 1995

Three dimensional turbulent flow fields around ships are simulated by a numerical method. Reynolds Averaged Navier-Stokes equations are used where Reynolds stresses are approximated by Baldwin-Lomax and Sub-Grid Scale(SGS) turbulence models. Body-fitted coordinate system is introduced to conform three dimensional ship geometries. The governing equations are discretized by a finite volume method. Temporal derivatives are approximated by the forward differencing and the convection terms are approximated by the QUICK or Kawamura scheme. The 2nd-order centered differencing is used for other spatial derivatives. Pressure and velocity fields are simultaneously iterated by the Highly Simplified Marker-And-Cell method. To verity the numerical method and turbulence models, flow fields around ships are simulated and compared to the experiments.

• Journal of Mechanical Science and Technology
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• 제15권8호
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• pp.1188-1195
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• 2001

A numerical analysis has been carried out to investigate the influences of thermosolutal convection on the heat and mass transfer and solute segregation in crystals grown by the vertical Bridgman technique. The governing equations are solved by a finite-volume method using the power law scheme and the SIMPLE algorithm in which body-fitted coordinate system has been used. A primary convective cell driven by thermal gradients forms in the bulk of the domain, while a secondary convective cell driven by solutal gradients forms near interface. As the solutal Rayleigh number increases, secondary cell becomes to be stronger and has a great influence on the radial concentration along the interface.

• 대한기계학회논문집B
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• 제22권12호
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• pp.1796-1804
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• 1998

A numerical investigation has been performed to discuss the radiation-affected steady-laminar natural convection induced by a hot inner cylinder under a large temperature difference in the annuli filled with a gray gas. To examine the effects of thermal radiation on thermo-fluid dynamic behaviors in the eccentric geometry, the generalized body-fitted coordinate system is introduced while the finite volume method (FVM) is used for solving the radiative transport equation. After validating the numerical results for the case without radiation, the detailed radiation effect has been discussed. Based on the results of this study, when there exists a large temperature difference between two cylinders, the existence of radiatively participating medium is found to incur a distinct difference in fluid dynamic as well as thermal behavior.

• 한국전산유체공학회지
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• 제8권1호
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• pp.8-15
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• 2003

Three-dimensional endwall flow within a linear cascade passage of high performance turbine blade is simulated with a 3-D Wavier-Stokes CFD code (MOSA3D), which is based on body-fitted coordinate system, pressure-correction and finite volume method. The endwall flow characteristics, including the development and generation of horseshoe vortex, passage vortex, etc. are clearly simulated, consistent with the generally known tendency. The effects of both turbulence model and convective differencing scheme on the prediction performance of endwall flow are systematically analyzed in the present paper. The convective scheme is found to have stronger effect than the turbulence model on the prediction performance of endwall flow. The present simulation result also indicates that the suction leg of the horseshoe vortex continues on the suction side until it reaches the trailing edge.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.102-108
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• 2002

Numerical analysis has been conducted in order to simulate the flow characteristics by tip clearance of turbine cascades. A 3-D Navier-Stokes CFD code based on body-fitted coordinate system, pressure-correction and finite volume method has been used along with a commercial CFD code. The present results have showed that the development and generation of leakage vortex, vortex within tip clearance, etc. are clearly simulated, consistent with the generally known tendency. The leakage vortex occurs mainly by a separation of leakage flow that arises due to a pressure difference between two surfaces of the blade at the tip.

• 한국주조공학회지
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• 제29권1호
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• pp.33-37
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• 2009

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. In this paper, we propose a new method that can consider the cutting cells which are cut by casting and mold based on the partial 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 grid 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. By using the cut cell method, performance of computation gets better because of reducing the whole number of meshes.

• 대한조선학회논문집
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• 제30권1호
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• pp.104-114
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• 1993

본 논문에서는 점성유동에 미치는 자유표면의 영향을 조사하기 위하여 자유표면을 수직으로 관통하는 원통 주위의 유동을 수치 시뮬레이션 하였다. 수치해석 방법으로서 Artificial Compressibility Method를 사용하였으며, 계산은 낮은 레이놀드수의 영역에 국한하였다. 계산결과는 자유표면에 가까운 유체영역에서 유선, 점성항력 등에 적지않은 영향이 있음을 보여주고 있다. 자유표면의 존재는 물체 후류 중의 와류를 물체로 부터 분리시키는 방향으로, 점성항력을 감소시키는 방향으로 작용하는 것으로 보인다.

• Journal of Mechanical Science and Technology
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• 제15권1호
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• pp.88-97
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• 2001

The present study numerically investigates the fuel-air mixing characteristics, flame structure, and pollutant emission inside a double-swirler combustor. A PSR(Perfectly Stirred Reactor) based microstructural model is employed to account for the effects of finite rate chemistry on the flame structure and NO formation. The turbulent combustion model is extended to nonadiabatic flame condition with radiation by introducing an enthalpy variable, and the radiative heat loss is calculated by a local, geometry-independent model. The effects of turbulent fluctuation are taken into account by the joint assumed PDFs. Numerical model is based on the non-orthogonal body-fitted coordinate system and the pressure/velocity coupling is handled by PISO algorithm in context with the finite volume formulation. The present PSR-based turbulent combustion model has been applied to analyze the highly intense turbulent nonpremixed flame field in the double swirler combustor. The detailed discussions were made for the flow structure, combustion effects on flow structure, flame structure, and emission characteristics in the highly intense turbulent swirling flame of the double swirler burner.

• Wind and Structures
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• 제9권1호
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• pp.37-58
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• 2006

The paper describes a study about effects of upstream hills on design wind loads using two mathematical approaches: Computational Fluid Dynamics (CFD) and Artificial Neural Network (NN for short). For this purpose CFD and NN tools have been developed using an object-oriented approach and C++ programming language. The CFD tool consists of solving the Reynolds time-averaged Navier-Stokes equations and $k-{\varepsilon}$ turbulence model using body-fitted nearly-orthogonal coordinate system. Subsequently, design wind load parameters such as speed-up ratio values have been generated for a wide spectrum of two-dimensional hill geometries that includes isolated and multiple steep and shallow hills. Ground roughness effect has also been considered. Such CFD solutions, however, normally require among other things ample computational time, background knowledge and high-capacity hardware. To assist the enduser, an easier, faster and more inexpensive NN model trained with the CFD-generated data is proposed in this paper. Prior to using the CFD data for training purposes, extensive validation work has been carried out by comparing with boundary layer wind tunnel (BLWT) data. The CFD trained NN (CFD-NN) has produced speed-up ratio values for cases such as multiple hills that are not covered by wind design standards such as the Commentaries of the National Building Code of Canada (1995). The CFD-NN results compare well with BLWT data available in literature and the proposed approach requires fewer resources compared to running BLWT experiments.