• Journal of the Korean Society of Visualization
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• v.15 no.3
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• pp.52-56
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• 2017

In this study, we investigate the flow characteristics of lift-type disk which behaves the up-down motion using the large eddy simulation (LES) and immersed boundary method (IBM). Also, we perform the noise analysis using pressure field at 1.35 m distance and reveal the cause of noise to observe the vortical structure analysis of flow result. It is observed that vortical structure and wind shear were generated at leading edge and tower with high velocity deficit and flow separation. High magnitude of flow noise was observed in low frequency range which is from 30 Hz to 60 Hz. It was observed that vortical structure at leading edge was generated in frequency range from 33.3 Hz to 41.6 Hz. Temporal characteristic in vortical structure at leading edge was similar to noise characteristics, having the similar frequency ranges.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.6
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• pp.480-488
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• 2014

Vortex shedding which is the dominant feature of body wakes and of direct relevance to practical engineering problems, has been intensively studied for flows past a circular cylinder. In contrast, vortex shedding from a hydrofoil trailing edge has been studied to much less extent despite numerous practical applications. The physics of the problem is still poorly understood. The present study deals with $K{\acute{a}}rm{\acute{a}}n$ vortex shedding from a truncated trailing-edge hydrofoil in relatively high Reynolds number flows. The objectives of this paper are twofold. First, we aim to simulate unsteady turbulent flows past a two dimensional hydrofoil through a hybrid particle-mesh method and penalization method. The vortex-in-cell (VIC) method offers a highly efficient particle-mesh algorithm that combines Lagrangian and Eulerian schemes, and the penalization method enables to enforce body boundary conditions by adding a penalty term to the momentum equation. The second purpose is to investigate shedding frequencies of vortices behind a NACA 0009 hydrofoil operating at a zero angle of attack.

• Journal of the Korean Society of Visualization
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• v.14 no.3
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• pp.28-31
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• 2016

In this study, we investigate the wake characteristics in two cases which are laminar inflow and turbulent inflow. To solve the flow with wind turbines and its wake, we use large eddy simulation (LES) technique with actuator line method (ALM) and turbulent inflow of Turbsim. Turbulent inflow which contains the characteristic of the stable atmospheric boundary layer is used. We perform the quantitative analysis of velocity deficit and turbulence intensity in two cases. Time series of velocity deficit at the first, the second column in two cases are compared to observe the performance of wind turbine. The performance in the first column in laminar inflow is overestimated compared to that in turbulent inflow. And we observe that wake in the case with turbulent inflow drive to the span-wise direction and wake recovery in turbulent inflow is more effective. In quadrant analysis of Reynolds stress, the ejection and the sweep motion in turbulent inflow case are bigger than those in laminar inflow case.

• Journal of Korea Water Resources Association
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• v.45 no.5
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• pp.473-480
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• 2012

A two-dimensional depth-integrated hydrodynamic and a depth-averaged passive scalar transport models were developed by using a Compact Finite Volume Method (CFVM) which can assure a higher order accuracy. A typical wave current interaction experimental data set was compared with the computed results by the proposed CFVM model, and resonable agreements were observed from the comparisons. One and two dimensional scalar advection tests were conducted, and very close agreements were observed with very little numerical diffusion. Finally, a turbulent mixing simulation was done in an open channel flow, and a reasonable similarity with LES data was observed.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.718-722
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• 2009

하도 상황이 수역(水域)에서 식생역(植生域)으로 변화하여 최종적으로 육역화(陸域化)단계로의 천이가 진행되는 현상을 하도 육역화라고 한다. 하도 육역화는 하천의 생태환경적 측면에서 많은 문제들을 야기할 수 있으며, 단일 단면 하도의 복단면 고착화로 하천 통수 단면이 감소하여 하도의 홍수 관리 기능에 심각한 위해 요소로 작용할 수 있다. 본 연구는 하도 육역화 방지를 위한 수공구조물로서 말뚝을 설치하고 그 효과를 3차원 수치모형인 FLOW-3D를 이용하여 검토하였다. 수치 모의는 구조물 주변의 복잡한 흐름 모의를 위하여 복잡한 지형지물이 있는 경우에 많이 활용되는 LES(Large Eddy Simulation) 난류 모델을 적용하였으며 세굴 및 퇴적 영향을 알아보기 위하여 유사 세굴(Sediment Scour) 모델을 적용하였다. 하도 육역화 방지 수공구조물의 효과 검토를 위하여 모형 수로의 제방 근처에 말뚝을 설치하고 말뚝직경, 설치 간격 및 배열 등을 변화시켜 구조물 주변의 동수역학적 거동, 흐름분리 효과 및 세굴영향을 수치모의를 통하여 분석하였다. 분석 결과 말뚝에 의한 흐름 분리와 국부 세굴에 의하여 하상 퇴적이 상대적으로 감소되는 효과를 나타냈으며 설치간격이 수변으로부터 말뚝 두께의 2배 그리고 흐름방향으로 말뚝 두께의 2배 이내의 간격으로 설치하여야 더욱 효과적인 것으로 나타났다. 추후 다양한 수리모형 실험을 통한 검증과 다양한 조건에 대한 수치 모의를 통하여 하도 육역화 방지 기술을 개발할 수 있을 것으로 사료된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1761-1764
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• 2008

본 연구에서는 상용 3차원 수치모형 코드인 FLOW-3D를 이용하여 난류모형에 따른 유류-유사 분리기 내에서 유체의 흐름거동을 해석하였다. 우수로 인해 발생한 유출수는 유류, 유사 및 쓰레기 등을 포함하고 있기 때문에 3차원적 거동을 하고 다양한 흐름특성을 갖는다. 유류-유사 분리기는 도심지의 지하구조물로서 이러한 유출수의 수질을 개선하여 하천이나 강으로 흘려보내는 기능을 갖는다. 분리기내에서의 복잡한 흐름 거동을 해석하기위해 정류판과 유류흡착기로 구성된 유류-유사분리기를 제작하여 수치모의를 실시하였다. 유류-유사분리기로 유입되는 유입수에 포함된 유사는 유체의 흐름이 분리기내에 설치되어있는 정류판을 지나면서 여과되도록 하였고 유사와 함께 유입수에 포함된 유류는 유류흡착기를 통해 여과되도록 하였다. 기존의 수리실험 결과와 수치모의를 통한 연구결과에서 유입수에 포함된 유사와 유류는 유류흡착기를 설치하였을 경우 유사와 유류의 분류활동이 더 활발하게 이루어지는 것을 알 수 있었다. 따라서, 본 연구에서는 유사와 유류의 포획률을 증가시키기 위한 단계로서 유류-유사분리기에 유류흡착기를 설치하고 분리기내의 복잡한 흐름을 각각의 난류모형을 이용하여 비교분석하였다. 수치모의는 $\kappa$ - 모형과 LES(Large Eddy Simulation) 모형의 두가지 난류모형을 사용하였고, FLOW-3D를 이용하여 3차원 수치모의를 실시하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.3
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• pp.235-242
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• 2016

Among underwater noise sources around submerged bodies, turbulence-induced noise has not been well investigated because of the difficulty of predicting it. In computational aeroacoustics, a number of studies has been conducted using the Ffowcs Williamse-Hawkings (FW-H) acoustic analogy without consideration of quadrupole source term due to the unacceptable calculation cost. In this paper, turbulence-induced noise is predicted, including that due to quadrupole sources, using a large eddy simulation (LES) turbulence model and a developed formulation of permeable FW-H method with an open source computational fluid dynamics (CFD) tool-kit. Noise around a circular cylinder is examined and the results of using the acoustic analogy method with and without quadrupole noise are compared, i.e. the FW-H method without quadrupole noise versus the permeable FW-H method that includes quadrupole sources. The usability of the permeable FW-H method for the prediction of turbulence-noise around submerged bodies is shown.

• Journal of Power System Engineering
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• v.13 no.5
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• pp.25-33
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• 2009

In the present study, the numerical investigation has been carried out to see the effects of water mist sprays on the fire suppression mechanism. The special-purposed program named as FDS was used to simulate the interaction of fire plume and water mists. This program solves the fire-driven flows using LES turbulence model, the mixture fraction combustion model, the finite volume method of radiation transport for a non-scattering gray gas, and conjugate heat transfer between wall and gas flow. The computational domain was composed of a rectangular space dimensioned as $L{\times}W{\times}H=4.0{\times}4.0{\times}2.5\;m^3$ with a mist-injecting nozzle installed 1.0 m high from the fire pool. In this paper, two types of nozzles were chosen to compare the performance of the fire suppression. Numerical results showed that the nozzle, type A, with more orifices having smaller diameters had poorer performance than the other one, type B because the flow injected through side holes deteriorated the primary flow. The fire-extinguishing time of type A was 2.6 times bigger than that of type B.

• Journal of Ocean Engineering and Technology
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• v.27 no.4
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• pp.55-61
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• 2013

The numerical simulation using LES-WASS-3D is developed to investigate the wave run-up on the revetment along the canal. Interaction of ocean wave, current, and Kelvin wave is investigated on 40 conditions varying the number of ship, cruising direction, and relative cruising location of ships, when a 650TEU container cruises in the canal. The mean wave run-up heights on the revetment are compared for every simulated conditions. The largest height of wave run-up is generated at the C-pair condition and the wave run-up generated at the canal entrance is larger than that at the inside canal. When Kelvin waves is interacted with the current, the mean wave run-up height is increased approximate 10% compared with no current condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.5
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• pp.604-611
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• 2004

Simulation of three-dimensional turbulent flow with LES and DNS lakes much time and expense with currently available computing resources and requires big computing resources especially for high Reynolds number. The emerging alternative to provide the required computing power and working environment is the Grid computing technology. We developed the CFD code which carries out the parallel computing under the Grid environment. We constructed the Grid environment by connecting different PC-cluster systems located at two different institutes of Pusan National University in Busan and KISTI in Daejeon. The specification of PC-cluster located at two different institutes is not uniform. We run our parallelized computer code under the Grid environment and compared its performance with that obtained using the homogeneous computing environment. When we run our code under the Grid environment, the communication time between different computer nodes takes much larger time than the real computation time. Thus the Grid computing requires the highly fast network speed.