• 한국해양공학회지
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• 제31권3호
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• pp.183-188
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• 2017

This paper provides numerical results for the estimation of the efficiency of KRISO energy saving devices in the design stage. A finite volume method is used to solve Reynolds averaged Navier-Stokes (RANS) equations, where the SST k-$\omega$ model is selected for turbulence closure. The propeller rotating motion is determined using a rigid body motion (RBM) scheme, which is called a sliding mesh technique. The numerical analysis focuses on predicting the power reduction by the designed KRISO devices (K-DUCT) under a self-propulsion condition. The present numerical results show good agreement with the available experimental data. Finally, it is concluded that CFD can be a useful method, along with model tests, for assessing the performance of energy saving devices for propulsion efficiency improvement.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.462-468
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• 2004

Large eddy simulation(LES) methodology used to model isothermal non-swirling and swirling flows in a model gas turbine combustor. The LES solver was implemented on parallel computer consisting 16 processors. To verify the capability of LES code and characterize swirling flow, the results was compared with that of Reynolds Averaged Navier-Stokes(RANS) using k -$\epsilon$ model as well as experimental data. The results showed that the LES and RANS well predicted the mean velocity field of a non-swirling flow. Specially, the LES showed a very excellent prediction performance for the corner recirculation zone. In swirling flow, comparing with the results obtained by RANS, LES showed a better performance in predicting the mean axial and azimuthal velocities, and the central recirculation zone. Finally, unsteady phenomena of turbulent flow was examined with LES methodology.

• 대한조선학회논문집
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• 제38권4호
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• pp.1-10
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• 2001

비 압축성 점성 유동에 대한 RANS 방정식의 수치 해법을 사용해서 4상한(four quadrant) 조건에서 작동하는 박용 프로펠러 주위의 난류 유동과 프로펠러 단독 성능을 계산하였다. 4상한 조건의 단독 성능에 대한 실험결과가 존재하는 모형 프로펠러 P4381에 대하여 계산된 유동은 다양한 조건에서 프로펠러에 발생하는 3차원 유동박리를 포함한 복잡한 점성유동 특성을 잘 보여주었으며, 계산된 프로펠러 추력과 토크는 실험에서 캐비테이션이 심하게 발생된 일부 경우를 제외하고는 실험 결과와 잘 일치하였다.

• 국제초고층학회논문집
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• 제8권4호
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• pp.291-302
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• 2019

We performed calculations combining optimization technologies and Computational Fluid Dynamics (CFD) aimed at reducing wind forces and mitigating wind environments (local strong winds) around buildings. However, the Reynolds Averaged Navier-stokes Simulation (RANS), which seems somewhat inaccurate, needs to be used to create a realistic CFD optimization tool. Therefore, in this study we explored the possibilities of optimizing calculations using RANS. We were able to demonstrate that building configurations advantageous to wind forces could be predicted even with RANS. We also demonstrated that building layouts was more effective than building configurations in mitigating local strong winds around tall buildings. Additionally, we used the Convolutional Neural Network (CNN) as an airflow prediction method alternative to CFD in order to increase the speed of optimization calculations, and validated its prediction accuracy.

• 대한조선학회논문집
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• 제50권5호
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• pp.282-290
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• 2013

The effects of the combination of blade number for forward and after propeller on the propeller shaft forces of a contra-rotating propeller (CRP) system are presented in the paper. The research is performed through the numerical simulations based on the Reynolds-Averaged Navier-Stokes equations (RANS). The simulation results of the present method in open water condition are validated comparing with the experimental data as well as the other numerical simulation results based on the potential method for 4-0-4 CRP (3686+3687A) and 4-0-5 CRP (3686+3849) of DTNSRDC. Two sets of CRP are designed and simulated to study the effect of the combination of blade number in behind-hull condition. One set consists of 3-blade and 4-blade, while the other is 4-blade and 4-blade. A full hull body submerged under the free surface is modeled in the computational domain to simulate directly the wake field of the ship at the propeller plane. From the simulation results, the fluctuations of axial force and moment are dominant in the case of same blade numbers for forward and after propellers, whereas the fluctuations of horizontal and vertical forces and moments are very large in the case of different blade numbers.

• 대한조선학회논문집
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• 제53권6호
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• pp.494-502
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• 2016

The accurate assessment of hull-appendage interaction in the early design stage is important to control the inflow to the propeller plane, which can cause undesirable hydrodynamic effects in terms of cavitation phenomenon. This paper describes a numerical analysis for the flow around a fully appended surface ship model for which KRISO has carried out a model test in the Large Cavitation Tunnel(LCT). This numerical study was performed with the LCT model test in a complementary manner for a good reproduction of the wake distribution of surface ships. A second order accurate finite volume method provided by a commercial computational fluid dynamics(CFD) program was used to solve the governing Reynolds Averaged Navier-Stokes(RANS) equations, where the SST $k-{\omega}$ model was used for turbulence closure. The numerical results were compared to available LCT experimental data for validation. The calculations gave good predictions for the boundary layer profiles on the walls of the empty cavitation tunnel and the wake at the propeller plane of the fully appended hull model in the LCT.

• 한국음향학회지
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• 제37권2호
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• pp.92-98
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• 2018

본 논문은 모형 프로펠러를 대상으로 공동수조 시험, 수중 충격시험, 유한요소해석 및 전산유체해석에 기반하여 수행한 명음 발생 메커니즘 연구이다. 선미 유동을 모사하기 위해 반류망, 프로펠러 및 방향타를 설치하고 수중청음기와 가속도계로 프로펠러 명음 현상의 발생과 소멸을 계측하였다. 유한요소해석을 통해 프로펠러 날개의 고유진동수를 예측하고 접촉 및 비접촉식 충격시험으로 이를 검증하였다. RANS(Reynolds Averaged Navier-Stokes) 방정식 기반 전산유체해석을 통하여 프로펠러 날개 각 단면의 유속과 유효 받음각을 계산하였으며, DES(Detached Eddy Simulation) 기반 고해상도 해석을 통해 명음 발생 위치에서 2-D 날개 단면 뒷전의 와류흘림주파수(vortex shedding frequency) 계산을 수행하였다. 수치적으로 예측된 와류흘림주파수는 모형시험으로 계측한 명음 발생 주파수 및 날개 고유진동수와 일치함을 확인하였다.

• 대한기계학회논문집B
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• 제35권8호
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• pp.763-771
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• 2011

본 연구에서는 환기용 축류송풍기에 대하여 효율을 목적함수로 하는 수치최적설계를 수행하였다. 유동해석은 삼차원 Reynolds-averaged Navier-Stokes(RANS) 방정식을 통하여 이뤄졌으며, 난류모델로는 Shear Stress Transport 모델을 사용하였다. 최적설계를 위한 설계변수로는 허브비, 날개의 중간 및 팁 스팬에서의 엇갈림각을 사용하였다. 실험계획법으로 라틴하이퍼큐브 샘플링 방법을 사용하여 설계영역 내에서 25개의 실험점을 추출하였다. 최적설계기법인 가중평균대리모델과 삼차원 RANS 해석을 결합하여 수치최적설계를 수행하였으며, 가중평균대리모델로는 WTA1, WTA2 및 WTA3 모델을 사용하였다. 수치 최적설계에 의해 얻어진 최적형상들의 성능을 기준형상과 비교하였으며, 성능이 가장 좋은 모델에 대하여 기준형상과의 내부유동장 비교 및 분석을 통해 성능이 향상된 원인을 규명하였다.

• Nuclear Engineering and Technology
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• 제53권11호
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• pp.3625-3634
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• 2021

The crossflow is the key phenomenon in turbulent flow inside rod bundles. In order to establish confidence on application of computational fluid dynamics (CFD) to simulate the crossflow in rod bundles, three Reynolds-Averaged Navier Stokes (RANS) models i.e. the realizable k-ε model, the k-ω SST model and the Reynolds stress model (RSM), and the Large Eddy simulations (LES) with the Wall-Adapting Local Eddy-viscosity (WALE) model are validated based on the Particle Image Velocimetry (PIV) flow measurement experiment in a 5 × 5 rod bundle. In order to investigate effects of periodic boundary condition in the gap, the numerical results obtained with four inner subchannels are compared with that obtained with the whole 5 × 5 rod bundle. The results show that periodic boundaries in the gaps produce strong errors far downstream of the spacer grid, and therefore the full 5 × 5 rod bundle should be simulated. Furthermore, it can be concluded, that the realizable k-ε model can only provide reasonable results very close to the spacer grid, while the other investigated models are in good agreement with the experimental data in the whole downstream flow in the rod bundle. The LES approach shows superiority to the RANS models.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2690-2695
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• 2007

This work presents numerical optimization for design of a blade stacking line of a low speed axial flow fan with a fast and elitist Non-Dominated Sorting of Genetic Algorithm (NSGA-II) of multi-objective optimization using three-dimensional Navier-Stokes analysis. Reynolds-averaged Navier-Stokes (RANS) equations with ${\kappa}-{\varepsilon}$ turbulence model are discretized with finite volume approximations and solved on unstructured grids. Regression analysis is performed to get second order polynomial response which is used to generate Pareto optimal front with help of NSGA-II and local search strategy with weighted sum approach to refine the result obtained by NSGA-II to get better Pareto optimal front. Four geometric variables related to spanwise distributions of sweep and lean of blade stacking line are chosen as design variables to find higher performed fan blade. The performance is measured in terms of the objectives; total efficiency, total pressure and torque. Hence the motive of the optimization is to enhance total efficiency and total pressure and to reduce torque.