• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1088-1094
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• 2002

A channel flow with a high Reynolds number but coarse grids is numerically studied to investigate the prediction possibility of its turbulence which is three-dimensional and time-dependent. In the present paper, a Reynolds-Averaged Navier-Stokes (RANS) model, a Large Eddy Simulation (LES) and a Navier-Stokes equation with no model are tested with a new approach of hybrid RANS/LES, which reduces to RANS model in the boundary layers and at separation, and to Smagorinsky-like LES downstream of separation, and then compared with each other. It is found that the simulations of hybrid RANS/LES method sustain turbulence like those of LES and with no model, and the results are stable and fairly accurate. This indicates strongly that gradual improvements could lead to a simple, stable, and accurate approach to predict turbulence phenomena of wall-bounded flow.

• 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.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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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.

• 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.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.437-441
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• 2010

LES results of turbulent premixed combustion flows are introduced by using the dynamic sub-grid scale model based on G-equation describing the flame front propagation. The turbulent premixed combustion flows around bluff body and over backward facing step are analyzed to validate present formation. LES of swirling partially premixed combustion flame is also performed to conform the predictive capabilities of LES model and to prompt our understanding for the combustion flows over double cone swirl burner combustor by using CFD-ACE+ commercial code.

• Wind and Structures
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• v.8 no.6
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• pp.407-426
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• 2005

A hybrid RANS/LES approach, based on the Limited Numerical Scales concept, is applied to the numerical simulation of the flow around a square cylinder. The key feature of this approach is a blending between two eddy-viscosities, one given by the $k-{\varepsilon}$ RANS model and the other by the Smagorinsky LES closure. A mixed finite-element/finite-volume formulation is used for the numerical discretization on unstructured grids. The results obtained with the hybrid approach are compared with those given by RANS and LES simulations for three different grid resolutions; comparisons with experimental data and numerical results in the literature are also provided. It is shown that, if the grid resolution is adequate for LES, the hybrid model recovers the LES accuracy. For coarser grid resolutions, the blending criterion appears to be effective to improve the accuracy of the results with respect to both LES and RANS simulations.

• 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.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.250-257
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• 2005

Large eddy simulation{LES) methodology used to model a bluff-body stabilized non-reacting flow. The LES solver was implemented on parallel computer consisting 16 processors. To verify the capability of LES code, 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 qualitatively well predicted the experimental results, such as mean axial, radial velocities and turbulent kinetic energy. However, in the quantitative analysis, 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.

• 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.

• Journal of Aerospace System Engineering
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• v.3 no.4
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• pp.41-49
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• 2009

This paper present result of numerical simulation of premixed combustion around a triangle Bluff Body. And a numerical simulation of a premixed flame stabilization by a bluff body was performed using LES Model. The calculated results from the LES showed a good agreement with experiment data than k-model. Premixture combustion has flammability limit, quenching distance, smallest ignition energy has the combustion quality of the back. Bluff body makes a recirculation zone. Therefor velocity of behind bluff body is very slow. It was caused by slowly position speed and the fire occurred after the Bluff Body. Occurrence of fire it made the waste gas of high speed and the thrust made well.