• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.168-171
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• 2008

In the present study, turbulent flows around cubic and L-shape buildings were simulated numerically. Standard ${\kappa}$-$\varepsilon$, RNG ${\kappa}$-$\varepsilon$, LES turbulence models were adopted for the present simulation. The wind pressure coefficients from these results were compared with the available experimental data. The result of RNG ${\kappa}$-$\varepsilon$ and LES turbulent models gave better prediction than that of standard ${\kappa}$-$\varepsilon$ turbulent model which is widely used in the turbulent flow simulation.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.6 s.150
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• pp.675-682
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• 2006

This study has investigated the turbulent flow around a square cylinder by using LES (large eddy simulation). Numerical simulations are performed for turbulent flow fields with Re = 22,000. The computed results are in good agreement with existing computational and experimental data. The time-averaged and phase-averaged turbulent statistics around a square cylinder are discussed. Total 20 phase bins extracted from one cycle period showed detailed wake structures of the phase-averaged flow field. The center of Karman vortex sheets did not deviated ${\pm}0.5$ from centerline of square cylinder while moving downstream.

• Journal of Ocean Engineering and Technology
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• v.18 no.2
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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).

• Wind and Structures
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• v.16 no.5
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• pp.491-515
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• 2013

Wind pressure characteristics on a double tower high-rise structure, which is disturbed by surrounding buildings, were investigated using large eddy simulation (LES) and 1:300 scale wind tunnel experiments. The computational simulation technique and wind tunnel experimental technique were described in detail initially. Comparisons of computational results with the experimental data have subsequently been carried out to validate the reliability of LES. Comparisons have been performed in detail for the mean and fluctuating pressure coefficients. Detailed explanations of each comparison were given in the paper. To study further on the pressure coefficients on the building surfaces, parametric studies on shape coefficient and spatial correlation were performed and investigated. The numerical and experimental results presented in this paper advance understanding on wind field around buildings and the application of LES and wind tunnel tests.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.239-243
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• 2012

This paper is concerned with turbulent flow computations using Large Eddy Simulation (LES) and the flow interaction of vortex shedding in a cylindrical duct flow driven by mass blowing through the wall. The purpose is to analyze non-linear combustion characteristics in the presence of vortex shedding generated in a hybrid rocket motor. Experimental studies have shown sudden changes in pressure (referred as a DC-shift), which depend on the strength of vortex strength of incoming flow. The combustion instability because of a sudden change in pressure fluctuations is mainly related with the interaction between vortex shedding. Therefore LES computation on a duct with injected normal blowing was performed to simulate the turbulent flow interactions with the behaviors of vortices and vortex structures along the injected wall.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.242-250
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• 2006

The impacts of equivalence ratio on the flow structure and flame dynamics in a model gas turbine combustor are investigated using large eddy simulation(LES). Dynamic k-equation model and G-equation flamelet model are employed as LES subgrid model for flow and combustion, respectively. As a result of mean flow field for each equivalence ratio, the increase of equivalence ratio brings about the decrease of swirl intensity through the modification of thermal effect and viscosity, although the same swirl intensity is imposed at inlet. The changes of vortical structure and turbulent intensity etc. near flame surface are occurred consequently. That is, the decrease of equivalence ratio can leads to the increase of heat release fluctuation by the more increased turbulent intensity and fluctuation of recirculation flow. In addition, the effect of inner vortex generated from vortex breakdown on the heat release fluctuation is increased gradually with the decrease of equivalence ratio. Finally, it can be identified that the variations of vortical structure play an important role in combustion instability, even though the small change of equivalence ratio is occurred.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.10
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• pp.1409-1416
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• 2000

In this study, turbulent flows in a planar combustor which has a square rib-type flame holder are numerically investigated by Large Eddy Simulation(LES). Firstly, the flow fields with or without jet injection downstream of the flame-holder are examined using uniform inlet velocity. Comparison of the present LES results with experimental one shows a good agreement. Secondly, to investigate mixing of oxidizer(air) and fuel injected behind the flame holder, the scalar-transport equation is introduced and solved. From the instantaneous flow and scalar fields, complex and intense mixing phenomena between fuel and jet are observed. It is shown that the ratio of jet to blocked air velocity is an important factor to determine the flow structure. Especially, when the ratio is large enough, the fuel jet penetrates the main vortices shed from the flame holder, resulting in significant changes in the flow and scalar fields.

• Journal of the Korean Society of Combustion
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• v.11 no.4
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• pp.27-35
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• 2006

The impacts of equivalence ratio on flow structure and flame dynamic in a model gas turbine combustor are investigated using large eddy simulation(LES). Dynamic k-equation model and G-equation flamelet model are employed as LES subgrid model for flow and combustion, respectively. As a result of mean flow field for each equivalence ratio, the increase of equivalence ratio brings about the decrease of swirl intensity through the modification of thermal effect and viscosity, although the same swirl intensity is imposed at inlet. The changes of vortical structure and turbulent intensity etc. near flame surface are occurred consequently. That is, the decrease of equivalence ratio can leads to the increase of heat release fluctuation by the more increased turbulent intensity and fluctuation of recirculation flow. In addition, the effect of inner vortex generated from vortex breakdown on the heat release fluctuation is increased gradually with the decrease of equivalence ratio. Finally, it can be identified that the variations of vortical structure play an important role in combustion instability, even though the small change of equivalence ratio is occurred.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.1
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• pp.55-63
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• 2012

The turbulent flow characteristics in a coaxial injector were investigated by the nonlinear $k-{\varepsilon}-f_{\mu}$ model of Park et al.[1] and large eddy simulation (LES). In order to analyze the geometric effects on the scalar mixing for nonreacting variable-density flows, several recessed lengths and momentum flux ratios are selected at a constant Reynolds number. The nonlinear $k-{\varepsilon}-f_{\mu}$�� model proposed the meaningful characteristics for various momentum flux ratios and recess lengths. The LES results showed the changes of small-scale structures by the recess. When the inner jet was recessed, the development of turbulent kinetic energy became faster than that of non-recessed case. Also, the mixing characteristics were mainly influenced by the variation of shear rates, but the local mixing was changed by the adoption of recess.

• 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.