• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.55-60
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• 2008

Turbulent flow characteristics on the gap of two parallel channels are investigated using LES(large eddy simulation) approach. Two parallel channels have the same cross-section area and are connected by the narrow channel named the gap. Turbulent flow near the gap makes the flow pulsation along the streamwise direction of two channels. The flow condition is the Reynolds number of $2.5{\times}10^{-5}$. We compared the predicted results with the previous experimental results and presented the axial mean velocity, turbulent intensities, Reynolds shear stresses and turbulent kinetic energy.

• 한국해양공학회지
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• 제18권2호
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• pp.1-9
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• 2004

As the first step to investigate the nonlinear interactions between turbulence and marine structures inside a viscous NWT, a LES technique was applied to solve the turbulent channel flow for =150. The employed turbulence models included 4 types: the Smagorinsky model, the Dynamic SGS model, the Structure Function model, and the Generalized Normal Stress model. The simulated data in time-series for the LESs were averaged in both time and space, and statistical analyses were performed. The results of the LESs were compared with those of a DNS, developed in the present study and two spectral methods by Yoon et al.(2003) and Kim et a1.(1987). Based on this research, the accuracy of LESs has been found to be still related to the number of grids for fine grid size).

• 대한조선학회논문집
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• 제55권3호
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• pp.265-273
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• 2018

Direct numerical and large eddy simulations of transitional flows around studs installed on flat plate and bulbous bow have been performed to investigate an effectiveness of turbulence stimulators on laminar-to-turbulence transition at a very low speed. The flow velocity was determined to be 0.366m/s corresponding to 4 knots of full-scale ship speed when the objective ship was Kriso container ship. The spatial evolution of skin friction coefficient disclosed that a fully development of turbulence was observed behind the second stud installed on flat plate while a rapid transition from laminar to turbulence gave rise to the fully development of turbulence behind the first stud installed on bulbous bow. A comparison of streamwise mean velocity profiles showed that the viscous sublayer and log-layer were in good agreement with previous results although the friction velocity of Smagrosinsky sub-grid scale model was about 10% larger than that of direct numerical simulation. While the turbulence intensities of bulbous bow was similar to those of flat plate in inner region, larger intensities of turbulence were observed in outer region of bulbous bow than those of flat plate.

• EDISON SW 활용 경진대회 논문집
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• 제2회(2013년)
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• pp.321-326
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• 2013

본 연구에서는 원형실린더의 강제 수평 및 수직진동에 따른 와흘림을 관찰하였다. EDISON_CFD의 가상경계법을 이용하여 원형실린더 주위 유동현상을 수치 모사하였다. 원형실린더의 강제 진동 특성에 따른 와흘림 진동수, 공력계수 등의 영향을 분석하였다. 특히, 진동방향에 따른 와흘림의 영향을 분석하여, 원형실린더의 강제 진동에 따른 유동의 선형성을 평가하였다.

• 대한조선학회논문집
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• 제41권1호
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• pp.47-54
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• 2004

The friction drag reduction of a ship is of prime importance for the design and production of high-valued/high-tech ship. Thus, this study carried out the development of reliable numerical tools to identify the friction drag reduction mechanism for turbulent boundary layer on the ship surface and to deduce the optimum reduction technique by numerical experiment. The developed LES and DNS numerical tools were applied to simulate the turbulent channel flow These results were very well matched with previous results not only qualitatively but also quantitatively. The parallelization using MPI (Message Passing Interface) technique implemented in the developed code to speed up the simulation and to obtain the accurate results from the fine grid system was testified its computational efficiency.

• 설비공학논문집
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• 제23권2호
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• pp.132-138
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• 2011

In the present article, we investigate numerically turbulent flow of air through compound rectangular channels. Large eddy simulation(LES) is employed for unsteady turbulence modeling. LES gives better predictions for the axial mean velocity distribution than those of other turbulent models. Strong large-scale quasi-periodic flow oscillations are observed in most of the geometries investigated. Such large-scale flow oscillations in compound rectangular channels are similar to the quasi-periodic flow pulsation through the gaps between fuel rod bundle in nuclear reactor. It exists in any longitudinal connecting gap between two flow channels. The frequency of this flow oscillation is determined by the geometry of the gap. The large scale cross motions through the rectangular compound channels induce significant heat transfer enhancement of the compound channel flow.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.204-212
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• 2003

As the first step to investigate the nonlinear interactions between turbulence and marine structures inside a viscous NWT, a LES technique was applied to the turbulent channel flow for $Re_{T}=150$, in this paper. The employed models were 4 types, such as the Smagorinsky model, the Dynamic SGS model, the Structure Function model and the Generalized Normal Stress model. The simulated data in time-series for the LESs were averaged in both time and space and performed statistical analysis. And results of the LESs were compared with those of a DNS developed in the present study and two spectral methods by Yoon et al.(2003) & Kim et al.(1987). It seems to be quite difficult to evaluate their performances to the present problem, but is seen that the accuracy of LESs are still related to the number of grids(or fine grid size).

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.928-933
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• 2003

For simulation of three-dimensional turbulent flow with LES and DNS takes much time and expense with current available computing resources. It is nearly impossible to simulate turbulent flow with high Reynolds number. So, the emerging alternative is the Grid computing for needed computation power and working environment. In this study, the CFD code was parallelized to adapt it for the parallel computing under the Grid environment. In the first place, the Grid environment was built to connect the PC-Cluster facilities belong to the different institutions using communication network system. And CFD applications were calculated to check the performance of the parallel code developed for the Grid environment. Although it is a fundamental study, it brings about a important meaning as first step in research of the Grid.

• 한국지반공학회논문집
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• 제28권8호
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• pp.5-19
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• 2012

준설매립지반 설계시 압밀 소요시간 단축을 위해 연직배수공법와 선행재하공법등의 연약지반 개량공법을 주로 적용한다. 준설매립지반의 자중에 의한 압밀이 완료되기까지는 많은 시간이 소요되므로 공사비 절감, 공기단축의 이유로 연약지반 개량공법은 일반적으로 자중압밀 도중 적용된다. 본 논문에서는 준설매립지반에서 연직방향으로 자중압밀이 진행되는 도중 연직배수재 타설에 의해 방사방향의 흐름이 추가로 발생하는 경우의 압밀거동 예측을 위하여 자중압밀을 고려한 2차원 축대칭 비선형 유한변형 압밀 지배방정식과 이를 적용하기 위한 수치모델(Axi-Selcon)을 개발하였다. Axi-Selcon의 검증과 자중압밀 도중 연직배수재가 타설된 준설매립지반을 모사하기 위해 일련의 실내시험을 수행하였다. 이를 위해 연직배수재가 타설된 준설매립지반을 모사하는 대형자중압밀 시험기를 고안하였다. 모델의 추가적인 검증을 위하여 기존에 제안된 간편 해석법을 적용한 결과와 Axi-Selcon의 해석결과와 비교하였다. 마지막으로, Axi-Selcon을 적용하여 가상의 대심도 준설매립지반의 거동을 예측하였다. 이와 같은 일련의 모델 검증과정을 통해 본 논문에서 개발된 Axi-Selcon은 자중압밀 도중 연직배수재 타설과 선행재하공법이 적용될 경우에 대한 초연약 준설매립지반의 압밀 거동을 적절히 예측할 수 있음을 보였다.

• 대한기계학회논문집B
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• 제36권1호
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• pp.103-110
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• 2012

EV double cone 버너를 장착한 스월 예혼합 연소기를 대상으로 LES 수치기법을 적용하여 연소기내의 유동 현상과 연료/공기 혼합, 화염 거동에 대해 조사하였고, 공연비와 압력 변화에 따른 NOx, CO 농도 변화를 예측하였다. 버너에서 발생한 강한 스월로 인해 재순환 영역이 발생하였으며, 희박 예혼합 화염은 버너 출구부터 형성되어 0.2 m 이내에 존재하는 것으로 나타났다. 상압, 공연비 38.7인 해석 조건에서 NOx 발생량은 연소기 출구에서 0.59 ppm으로 예측되었고, CO는 화염면에서 다량 생성되나 출구로 갈수록 급격히 산화되어 출구에서 5.25 ppm으로 낮게 예측되었다. 또한, NOx 배출량은 공연비가 높아질수록, 압력이 감소할수록 줄어드는 것으로 나타났다. 설계 변경을 통해 다양한 연료 공급 형태에서의 NOx 배출 특성을 조사하였으며, 5 lance-hole 분사의 경우 가장 적은 NOx 배출 특성을 보였다.