• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.11
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• pp.57-64
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• 2005

Large Eddy Simulation (LES) of turbulent premixed combustion flow is performed by using the dynamic subgrid scale model based on -equation describing the flame front propagation. After introducing the LES governing equations with dynamic subgrid scale (DSGS) model newly introduced into the -equation, the turbulent premixed combustion flow over backward facing step is analyzed to validate present formulation. The calculated results can predict the velocity and temperature of the combustion flow in good agreement with the experiment data.

• Journal of Energy Engineering
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• v.21 no.3
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• pp.228-236
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• 2012

Large eddy simulation (LES) is increasingly used as a tool for studying the dynamics of turbulence in combustion chamber flows due to the promise of wider generality and more accurate results compared to Reynolds averaged Navier-Stokes(RANS) models. This study presents the appropriate subgrid-scale(SGS) model in LES for predicting the turbulent flow field in the internal combustion engine. The study of the effects of model and numerical parameters such as discretization scheme, initial condition, time step and SGS model was performed. The results of LES using the SGS model were found to be in the good agreement with experimental data.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.247-247
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• 2022

제트류는 복잡한 흐름 중 하나로 다양한 크기의 에디가 다양한 운동량을 가지고 있다. 이러한 제트류를 구현하기 위해서는 난류 운동 에너지 등 제트류의 특성을 잘 반영하여야 한다. 제트를 구현하기 위해서는 수리학적 모델, 현장 실험 등 많은 방법이 있으며, 본 연구에서는 상대적으로 공간, 시간적 비용이 적게 드는 수치해석 방법을 사용하여 연구를 진행하였다. 대표적인 수치해석방법에는 DNS(Direct Numerical Simulation), LES(Large Eddy Simulation), RANS(Reynolds Averaged Navier Stokes) 등이 있다. RANS는 시간 평균 흐름 특성만 산출하며 제트의 복잡성을 재현하는 데 한계가 있어, 본 연구는 DNS와 LES 모델을 이용하여 제트류를 구현하는 것에 초점을 맞추었다. DNS는 해당 격자에서 발생하는 모든 에디를 직접 해석 때문에 난류 모델링이 필요하지 않지만, 많은 수의 그리드가 필요하여 수치해석 시 소요시간이 긴 편이다. LES는 대규모 에디는 직접 해석하지만 일정 크기 이하의 소용돌이를 해석하기 위해서 모델이 필요하다. 따라서 서브 그리드 모델에 따라 약간 다른 결과를 보인다. 이러한 문제점을 해결하기 위해 본 연구에서는 LES의 기존 서브 그리드 모델을 사용하지 않고 신경망 모델로 학습한 DNS 결과를 활용하는 방법을 제안한다. 우선 DNS와 LES 모델을 사용하여 에너지 스펙트럼을 비교하여 서브 그리드 모델이 시작하는 파수를 찾는다. 이후 특정 파수 아래의 작은 에디를 모사할 적절한 신경망 모델을 결정하여 DNS의 작은 에디를 신경망 알고리즘이 모사할 수 있도록 학습시킨다. 이후 기존 서브 그리드 모델을 사용하지 않고 학습된 신경망 알고리즘을 사용한 LES 모델이 모사한 제트류와 실제 DNS 모델을 사용한 제트류를 비교 및 평가한다.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2013.11a
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• pp.182-183
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• 2013

FDS(Fire Dynamics Simulator)는 국내에서 화재해석을 위해 사용되고 있는 가장 보편적인 소프트웨어 중의 하나이다. 미국의 NIST에서 25년간 지속적인 업그레이드를 통해 개발되어 오고 있으며 인터넷 상에서 무료로 배포되고 있어 전 세계의 화재관련 연구자 및 학생들이 연구 및 학습의 목적으로 사용하고 긴 기간동안 많은 전문가들에 의해 검증되어온 소프트웨어이다. 하지만 FDS가 난류해석을 위해 사용하고 있는 Smagorinsky의 LES(Large Eddy Simulation)모델은 현재까지 발표된 LES모델 중 가장 초기의 모델로서 건축물과 같이 복잡한 형상을 갖는 계산영역에서는 결과의 신뢰성이 많이 떨어지는 것으로 알려져 있다. 본 연구에서는 FDS의 대공간의 화재해석 성능을 평가하는 것을 목적으로 스페인 Murcia에서 수행된 Murcia Atrium Fire Test를 해석 대상으로 하여 FDS가 사용하고 있는 Smagorinsky의 LES모델 및 3가지의 다른 LES모델을 사용하여 대공간 내부의 연기유동을 해석하였으며 그 결과를 비교하였다.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.3
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• pp.423-433
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• 2004

A large eddy simulation (LES) is performed for turbulent flow in a combustion device. The combustion device is simplified as a cylindrical chamber with sudden expansion. A flame holder is attached inside a cylindrical chamber in order to promote turbulent mixing and to accommodate flame stability. The turbulent sub-grid scale models are applied and validated. Emphasis is placed on the evaluation of turbulent model for the LES of complex geometry. The simulation code is constructed by using a general coordinate system based on the physical contravariant velocity components. The calculated Reynolds number is 5000 based on the bulk velocity and the diameter of inlet pipe. The predicted turbulent statistics are evaluated by comparing with the LDV measurement data. The Smagorinsky model coefficients are estimated and the utility of dynamic SGS models are confirmed in the LES of complex geometry.

• Proceedings of the Korean Nuclear Society Conference
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• 2003.05a
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• pp.119-119
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• 2003

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.3
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• pp.507-514
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• 2009

Large eddy simulation code was developed to predict the turbulent flows over backward-facing steps including a recirculating flow phenomena. Localized dynamic ksgs-equation model was employed as a LES subgrid model and the LES solver was implemented on parallel computer consisting of 16 processors to reduce computational costs. The results of laminar flow showed qualitative and quantitative agreements between current simulations and experimental results availablein literatures. The simulation of the turbulent flows also yielded reasonable results. From these results, it can be expected that developed LES code will be very useful to analyze the combustion in stabilities and noise of a practical combustor in the future.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.304-309
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• 2017

This paper studies a nonpremixed turbulent flame in a model scramjet combustor using zonal hybrid RANS/LES method. The numerical domain is divided into two region, RANS and LES region. The interface between the two regions is treated with synthetic eddy method. A model scramjet combustor experimented at German aerospace center is selected for the comparative study. The fuel injection of cracked kerosene surrogate which is composed of ethylene and methane is considered. Turbulent combustion of cracked kerosene surrogate is achieved using flamelet approach.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.202-207
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• 2009

In this study, Numerical simulations were performed to analyze the characteristics of fire driven smoke flow for different location of fire source in the deeply underground subway station with using FDS code. The fire driven smoke-flow which was simulated by using Parallel Computational Method for fast calculation and LES for turbulence model. In this research, the fire location to obstruct a suitable egress from the fire disaster were discussed.

• Journal of computational fluids engineering
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• v.17 no.3
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• pp.11-17
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• 2012

In this study, aerodynamic analyses have been conducted for 4-Bladed Vertical-Axis Wind Turbine (VAWT) configuration and the results are compared with experimental data. Reynolds-averaged Navier-Stokes equation with LES turbulence model is solved for unsteady flow problems. In addition, the computation results by standard k-${\omega}$ and SST k-${\omega}$ turbulence models are also presented and compared. An experiment model of 4-Bladed VAWT model has been designed and constructed herein. Experimental tests for aerodynamic performance of the present VAWT model are practically conducted using the vehicle mounted testing system. Comparison results between the experiment and the computational fluid dynamics (CFD) analyses are presented in order to show the accuracy of CFD analyses using the different turbulent models.