• 한국전산유체공학회지
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• 제11권4호
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• pp.32-38
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• 2006

The objective of this study is to evaluate the prediction accuracy of development large eddy simulation(LES) program for turbulent flow behind a bluff-body. The LES solver was implemented on parallel computer consisting 16 processors. To verify the capability of LES code, the results were compared with those of Reynolds Averaged Navier-Stokes(RANS) using standard ${\kappa}-{\varepsilon}$ model as well as experimental data. The results showed that the LES and RANS qualitatively well predicted the experimental results, such as mean axial, radial velocities and turbulent kinetic energy. In the quantitative analysis, however, the LES showed a better prediction performance than RANS. Specially, the LES well described characteristics of the recirculation zones, such as air stagnation point and jet stagnation point. Finally, the unsteady phenomena on the Bluff-body, such as the transition of recirculation region and vorticity, was examined with LES methodology.

• 대한조선학회논문집
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• 제45권2호
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• pp.109-123
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• 2008

The present paper presents the CFD result for a beam wave test case. An ONR tumblehome ship model with bilge keels is used. The beam wave test is for zero forward speed and roll and heave 2DOF with wave slope $a_k=0.156$ and wavelength ${\lambda}=1.12L_{PP}$, with $L_{PP}$ the ship length. The problems is solved numerically with an unsteady Reynolds averaged Navier-Stokes approach. The free surface flow is computed using a single-phase level-set method and the motions in each time step are integrated using a predictor-corrector iteration approach which uses dynamic overset grids moving with relative ship motion. The predicted CFD results for motions and forces are compared with experimental data, showing a reasonable agreement.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.729-732
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• 2010

본 연구는 케로신과 액체산소를 추진제로 사용하는 동축 와류형 분사기를 해석하기 위해 체계적인 물리 모델링을 수행하였다. 먼저 초임계 압력 조건에서 나타나는 실제유체의 열역학 및 전달 물성치를 계산할 수 있는 서브루틴 라이브러리를 구축하였으며, 층류 화염편 해석 코드와 연동하여 케로신 난류연소장의 국소화염구조를 해석하였다. 설계 목적에 맞는 계산 효율성을 확보하기 위해 동축 와류형 분사기는 RANS 기반의 2차원 축대칭 선회 유동으로 해석하였으며, 실험 결과가 존재하는 비연소 동축선회 제트 유동을 통해 예측정확도를 검증하였다. 실제 고압 연소를 수반하는 동축 와류형 분사기의 경우, 기존의 RANS 모델은 급격한 밀도 구배가 수반되는 선회 막 유동의 혼합층에서 과도한 난류확산을 야기하였으며, 난류모델의 수정을 위해 보다 심도 있는 연구가 필요할 것으로 판단되었다.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2002년도 추계학술발표회요약집
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• pp.161-161
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• 2002

• 한국해양공학회지
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• 제33권4호
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• pp.313-321
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• 2019

The prediction of the hydrodynamic performance of a planing hull vessel is an important and challenging topic for computational fluid dynamic (CFD) applications to naval hydrodynamics. In this paper, the resistance and planing attitude analysis for a Fridsma hull, which is a prismatic planing hull, in still water are numerically studied using OpenFOAM. OpenFOAM is an open source code package based on C++ libraries and the finite volume method (FVM) for the discretization of the RANS equation. The volume of fluid method (VOF) is used to capture the water-air interface and the SST ${\kappa}-{\omega}$ model is used for the turbulence simulation. The overset mesh method is used to capture the large motion of the hull at higher speeds. Before the extensive analysis, uncertainty analyses using various time steps and grid sizes were performed for one ship speed case of Fn = 1.19. The results of the present study are compared with those of a model test, other CFD research, and Savitsky's empirical formula. The results of the present study, following the trend of other CFD results, slightly over predict the resistance and under predict the sinkage and, more significantly, the trim.

• Journal of Mechanical Science and Technology
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• 제20권9호
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• pp.1514-1524
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• 2006

This work presents the three-dimensional analysis of flow and heat transfer performed for a wire-wrapped fuel assembly of liquid metal reactor using Reynolds-averaged Wavier-Stokes analysis in conjunction with 557 model as a turbulence closure. The whole fuel assembly has been analyzed for one period of the wire-spacer using periodic boundary conditions at inlet and outlet of the calculation domain. Three different assemblies, two 7-pin wire-spacer fuel assemblies and one bare rod bundle, apart from the pressure drop calculations for a 19-pin case, have been analyzed. Individual as well as a comparative analysis of the flow field and heat transfer have been discussed. Also, discussed is the position of hot spots observed in the wire-spacer fuel assembly. The flow field in the subchannels of a bare rod bundle and a wire-spacer fuel assembly is found to be different. A directional temperature gradient is found to exist in the subchannels of a wire-spacer fuel assembly Local Nusselt number in the subchannels of wire-spacer fuel assemblies is found to vary according to the wire-wrap position while in case of bare rod bundle, it's found to be constant.

• 한국항공우주학회지
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• 제39권3호
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• pp.201-209
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• 2011

NREL Phase VI 수평축 풍력터빈 주위의 3차원 유동에 대하여 미끄럼 격자 기법을 사용한 비정상 RANS 해석을 수행하였다. 블레이드/타워의 간섭영향을 해석하기 위하여 로터단일과 로터/타워/나셀의 2가지 해석 모델을 구축하였다. 로터/타워/나셀의 해석 결과를 NREL의 실험데이터와 비교하여 CFD 해석모델의 유용성을 확인하였다. 두 모델에 의한 해석 결과의 비교를 통하여 비록 상풍형 풍력터빈으로서 작기는 하지만 타워/나셀의 영향이 확실히 나타나는 것을 확인하였다. 다른 가시화 결과와 토크를 포함한 적분 공력하중 등도 구축한 CFD 모델의 비정상 유동해석 능력이 효과적임을 보여주고 있다.

• 대한조선학회논문집
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• 제55권5호
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• pp.385-393
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• 2018

In this study, the analysis of 2DOF (2 Degree Of Freedom) motion and added resistance of a ship in regular head waves is carried out using RANS (Reynolds Averaged Navier-Stokes) approach. In order to improve the accuracy for large amplitude motions, the dynamic overset scheme is adopted. One of the dynamic overset schemes, Suggar++ is applied to WAVIS which is the in-house RANS code of KRISO (Korea Research Institute of Ships and Ocean Engineering). The grid convergence test is carried out using the present scheme before the analysis. The target hull form is KRISO VLCC tanker (KVLCC2) and 13 wave length conditions are applied. The present scheme shows the improved results comparing with the results of WAVIS2 in the non-inertial reference frame. The dynamic overset scheme is confirmed to give the comparatively better results for the large amplitude motion cases than the non-inertial frame based scheme.

• 대한조선학회논문집
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• 제37권1호
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• pp.60-66
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• 2000

고속 프로펠러를 대상으로 캐비테이션 발생 특성에 가장 큰 영향을 미치는 2차원 날개단면의 앞날 형상에 관한 연구를 수행하였다. 앞날 주위의 유동장을 해석하기 위하여 비압축성 RANS(Reynolds Averaged Navier-Stokes)방정식을 유한체적법(FVM)으로 차분하는 수치해석기법을 사용하였다. 또한 패널법을 이용하여 캐비테이션 발생두께를 예측하였다. 예측된 결과들은 실험결과와 비교해서 타당함을 알 수 있었으며, 이 결과를 이용하여 새로운 단면을 설계하였다.

• 한국전산유체공학회지
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• 제9권2호
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• pp.62-69
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• 2004

The present work solved 3D incompressible RANS equations on a rotating, multi-blocked grid system to efficiently analyze ducted marine propulsor with the interaction of propeller guidevane and annular duct. To handle the interface boundary between the guidevane and the propeller, a sliding multiblock technique based on the cubic spline interpolation was applied. To validate the present code, a turbine flow was simulated and the time-averaged pressure coefficients were compared with experiment. After the code validation, the flowfield around a ducted marine propeller with pre-swirl guidevane was simulated.