• Title/Summary/Keyword: Large-Eddy Simulation LES

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Analysis of Smoke Spread Effect Due to The Fire Location in Underground Subway-Station (대심도 역사의 화재위치에 따른 연기확산 영향 분석)

  • Jang, Yong-Jun;Koo, In-Hyuk;Kim, Jin-Ho;Nam, Seong-Won
    • Proceedings of the KSR Conference
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    • 2011.10a
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    • pp.2885-2890
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    • 2011
  • Simulation study were performed for fire location effect on the smoke spread in the deeply-underground subway station(DUSS). In this research, Shingumho station (The line # 5, Depth: 46m) has been selected as case-study for the analysis of smoke-spread effect with the different fire location. Field test data measured for actual fan in DUSS was applied as a condition of a simulation. The whole station was covered in this analysis and 4 million grids were generated for this simulation. The fire driven flow was analyzed case by case to compare the smoke-spread effect according to the fire location. In order to enhance the efficiency of calculation, parallel processing by MPI was employed and LES(large eddy simulation) method in FDS code was adopted.

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DNS and Analysis on the Interscale Interactions of the Turbulent Flow past a Circular Cylinder for Large Eddy Simulation (원형 실린더를 지나는 난류 유동장의 직접수치해석과 큰 에디모사를 위한 스케일 간 상호작용 연구)

  • Kim, Taek-Keun;Park, No-Ma;Yoo, Jung-Yul
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1801-1806
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    • 2004
  • Stochastic nature of subgrid-scale stress causes the predictability problem in large eddy simulation (LES) by which the LES solution field decorrelates with field from filtered directnumerical simulation (DNS). In order to evaluate the predictability limit in a priori sense, the information on the interplay between resolved scale and subgrid-scale (SGS) is required. In this study, the analysis on the inter-scale interaction is performed by applying tophat and cutoff filters to DNS database of flow over a circular cylinder at Reynolds number of 3900. The effect of filter shape is investigated on the interpretation of correlation between scales. A critique is given on the use of tophat filter for SGS analysis using DNS database. It is shown that correlations between Karman vortex and SGS kinetic energy drastically decrease when the cutoff filter is used, which implies that the small scale universality holds even in the presence of the large scale coherent structure.

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A Basic Study on the Aero-acoustic Noise Characteristics around a Circular Cylinder using the Large Eddy Simulation (대와류모사법을 이용한 원주 주위의 공력소음 특성에 관한 기초연구)

  • Mo, Jang-Oh;Lee, Young-Ho
    • The KSFM Journal of Fluid Machinery
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    • v.13 no.3
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    • pp.5-11
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    • 2010
  • As a basic study of the aero-acoustic noise, Large eddy simulations were carried out for a fixed circular cylinder at Renolds number (Re=$9.0\times10^4$) using commercial CFD code, FLUENT. The subgrid-scale turbulent viscosity was modeled by Smagorinsky-Lilly model adapted to structured meshes. The results of analysis showed that time-averaged value, $\bar{C}_D$ is approximately 1.47 which is considerably adjacent with the experimentally measured value of 1.32 in comparison to the values performed by previous researchers. It is observed that there are the very small acoustic pressure fluctuation with the same frequency of the Karman vortex street.

On Large Eddy Simulation with Centered and Upwind Compact Difference Schemes (중심 및 상류 컴팩트 차분기법을 적용한 난류유동의 LES)

  • Park Noma;Yoo Jung Yul;Choi Haecheon
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.807-810
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    • 2002
  • The suitability of high-order accurate, central and upwind-biased compact difference schemes is evaluated for the large-eddy simulations of flows in complex geometry. Two flow geometries are considered: channel and circular cylinder. The effects of numerical dissipation and aliasing error on the evaluation of subgrid scale stress are investigated by extending the analysis by Ghosal (1) to centered and upwind compact schemes. It is shown that the failure of upwind schemes mainly comes from the aliasing error.

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On the Suitability of Centered and Upwind-Biased Compact Difference Schemes for Large Eddy Smulations (II) - Static Error Analysis - (LES에서 중심 및 상류 컴팩트 차분기법의 적합성에 관하여 (II) - 정적 오차 해석 -)

  • Park, No-Ma;Yoo, Jung-Yul;Choi, Hae-Cheon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.7
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    • pp.984-994
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    • 2003
  • The suitability of high-order accurate, centered and upwind-biased compact difference schemes for large eddy simulation is evaluated by a spectral, static error analysis. To investigate the effect of numerical dissipation on LES solutions, power spectra of discretization errors are evaluated for isotropic turbulence models in both continuous and discrete wavevector spaces. Contrary to the common belief, the aliasing errors from upwind-biased schemes are larger than those from comparable non-dissipative schemes. However, this result is the direct consequence of the definition of the power spectral density of the aliasing error, which poses the limitation of the static error analysis for upwind schemes.

A Study of 3-Dimensional Turbulent Channel Flow Using Discrete Wavelet Transform (이산 웨이블릿 변환을 이용한 3차원 난류 채널 유동에 관한 연구)

  • Kim Kangshik;Lee Sanghwan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.3 s.234
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    • pp.314-321
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    • 2005
  • Discrete Wavelet Transform (DWT) has been applied to the Direct Numerical Simulation (DNS) data of turbulent channel flow. DWT splits the turbulent flow into two orthogonal parts, one corresponding to coherent structures and the other to incoherent background flow. The coherent structure is extracted from not vorticity field but velocity's since the channel flow is not isoropic. By comparing DWT's result of channel flow with that of isotropic flow, it is shown that coherent structure maintains the properties of original channel flow. The velocity field of coherent structures can be represented by few wavelet modes and that these modes are sufficient to reproduce the velocity probability density function (PDF) and the energy spectrum over the entire inertial range. The remaining incoherent background flow is homogeneous, has small amplitude, and is uncorrelated. These results are compared with those obtained for the same compression rate using large eddy simulation (LES) filtering. In contrast to the incoherent background flow of DWT, the LES subgrid scales have a much larger amplitude and are correlated, which makes their statistical modeling more difficult.

A Study of 3-Dimensional Turbulent Channel Flow using Discrete Wavelet Transform (이산 웨이블릿 변환을 이용한 3차원 난류 채널 유동에 관한 연구)

  • Kim, Kang-Shik;Lee, Sang-Hwan
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1813-1818
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    • 2004
  • Discrete Wavelet Transform (DWT) has been applied to the Direct Numerical Simulation (DNS) data of turbulent channel flow. DWT splits the turbulent flow into two orthogonal parts, one corresponding to coherent structures and the other to incoherent background flow. The coherent structure is extracted from not vorticity field but velocity's since the channel flow is not isotropic. By comparing DWT's result of channel flow with that of isotropic flow, it is shown that coherent structure maintains the properties of original channel flow. The velocity field of coherent structures can be represented by few wavelet modes and that these modes are sufficient to reproduce the velocity probability distribution function (PDF) and the energy spectrum over the entire inertial range. The remaining incoherent background flow is homogeneous, has small amplitude, and is uncorrelated. These results are compared with those obtained for the same compression rate using large eddy simulation (LES) filtering. In contrast to the incoherent background flow of DWT, the LES subgrid scales have a much larger amplitude and are correlated, which makes their statistical modeling more difficult.

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Comparative Study on The Numerical Simulation for The Back-Layer of The Tunnel Fire-Driven Flow with LES and RANS (터널화재유동의 역기류 해석을 위한 LES 및 RANS 결과의 비교 고찰)

  • Jang, Yong-Jun;Kim, Hag-Beom;Kim, Jin-Ho;Han, Seok-Youn
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.3
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    • pp.156-163
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    • 2009
  • In this study, comparative analysis on the back-layer phenomena in the tunnel-fire driven flow is performed using numerical simulation with LES and RANS. FDS(Fire Dynamics Simulator) code is employed to calculate the fire-driven turbulent flow for LES and Smartfire code is used for RANS. Hwang and Wargo's data of scaling tunnel fire experiment are employed to compare with the present numerical simulation. The modeled tunnel is 5.4m(L) ${\times}$ 0.4m(W) ${\times}$ 0.3m(H). Heat Release Rate (HRR) of fire is 3.3kW and ventilation-velocity is 0.33m/s in the main stream. The various grid-distributions are systematically tested with FDS code to analyze the effects of grid size. The LES method with FDS provides an improved back-layer flow behavior in comparison with the RANS (${\kappa}-{\epsilon}$) method by Smartfire. The FDS solvers, however, overpredict the velocity in the center region of flow which is caused by the defects in the tunnel-entrance turbulence strength and in the near-wall turbulent flow in FDS code.

Large eddy simulation of wind effects on a super-tall building

  • Huang, Shenghong;Li, Q.S.
    • Wind and Structures
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    • v.13 no.6
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    • pp.557-580
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    • 2010
  • A new inflow turbulence generation method and a combined dynamic SGS model recently developed by the authors were applied to evaluate the wind effects on 508 m high Taipei 101 Tower. Unlike the majority of the past studies on large eddy simulation (LES) of wind effects on tall buildings, the present numerical simulations were conducted for the full-scale tall building with Reynolds number greater than $10^8$. The inflow turbulent flow field was generated based on the new method called discretizing and synthesizing of random flow generation technique (DSRFG) with a prominent feature that the generated wind velocity fluctuations satisfy any target spectrum and target profiles of turbulence intensity and turbulence integral length scale. The new dynamic SGS model takes both advantages of one-equation SGS model and a dynamic production term without test-filtering operation, which is particular suitable to relative coarse grid situations and high Reynolds number flows. The results of comparative investigations with and without generation of inflow turbulence show that: (1) proper simulation of an inflow turbulent field is essential in accurate evaluation of dynamic wind loads on a tall building and the prescribed inflow turbulence characteristics can be adequately imposed on the inflow boundary by the DSRFG method; (2) the DSRFG can generate a large number of random vortex-like patterns in oncoming flow, leading to good agreements of both mean and dynamic forces with wind tunnel test results; (3) The dynamic mechanism of the adopted SGS model behaves adequately in the present LES and its integration with the DSRFG technique can provide satisfactory predictions of the wind effects on the super-tall building.

LES OF TURBULENT PREMIXED COMBUSTION FLAME AND LES APPLICATION FOR THE INDUSTRIAL COMBUSTOR DEVELOPMENT (난류 예혼합연소 화염의 LES 및 산업용 연소기 개발을 위한 LES 응용 해석 기술)

  • Park, Nam-Seob;Ryu, Jong-Hyuk
    • 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.

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