• Title, Summary, Keyword: Large Eddy simulation

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DETACHED EDDY SIMULATION OF BASE FLOW IN SUPERSONIC MAINSTREAM (초음속 유동장에서 기저 유동의 Detached Eddy Simulation)

  • Shin, J.R.;Won, S.H.;Choi, J.Y.
    • 한국전산유체공학회:학술대회논문집
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    • pp.104-110
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    • 2008
  • Detached Eddy Simulation (DES) is applied to an axisymmetric base flow at supersonic mainstream. DES is a hybrid approach to modeling turbulence that combines the best features of the Reynolds-averaged Navier-Stokes (RANS) and large-eddy simulation (LES) approaches. In the Reynolds-averaged mode, the model is currently based on either the Spalart-Allmaras (S-A) turbulence model. In the large eddy simulation mode, it is based on the Smagorinski subgrid scale model. Accurate predictions of the base flowfield and base pressure are successfully achieved by using the DES methodology with less computational cost than that of pure LES and monotone integrated large-eddy simulation (MILES) approaches. The DES accurately resolves the physics of unsteady turbulent motions, such as shear layer rollup, large-eddy motions in the downstream region, small-eddy motions inside the recirculating region. Comparison of the results shows that it is necessary to resolve approaching boundary layers and free shear-layer velocity profiles from the base edge correctly for the accurate prediction of base flows. The consideration of an empirical constant CDES for a compressible flow analysis may suggest that the optimal value of empirical constant CDES may be larger in the flows with strong compressibility than in incompressible flows.

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DETACHED EDDY SIMULATION OF BASE FLOW IN SUPERSONIC MAINSTREAM (초음속 유동장에서 기저 유동의 Detached Eddy Simulation)

  • Shin, J.R.;Won, S.H.;Choi, J.Y.
    • 한국전산유체공학회:학술대회논문집
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    • pp.104-110
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    • 2008
  • Detached Eddy Simulation (DES) is applied to an axisymmetric base flow at supersonic mainstream. DES is a hybrid approach to modeling turbulence that combines the best features of the Reynolds-averaged Navier-Stokes RANS) and large-eddy simulation (LES) approaches. In the Reynolds-averaged mode, the model is currently based on either the Spalart-Allmaras (S-A) turbulence model. In the large eddy simulation mode, it is based on the Smagorinski subgrid scale model. Accurate predictions of the base flowfield and base pressure are successfully achieved by using the DES methodology with less computational cost than that of pure LES and monotone integrated large-eddy simulation (MILES) approaches. The DES accurately resolves the physics of unsteady turbulent motions, such as shear layer rollup, large-eddy motions in the downstream region, small-eddy motions inside the recirculating region. Comparison of the results shows that it is necessary to resolve approaching boundary layers and free shear-layer velocity profiles from the base edge correctly for the accurate prediction of base flows. The consideration of an empirical constant CDES for a compressible flow analysis may suggest that the optimal value of empirical constant CDES may be larger in the flows with strong compressibility than in incompressible flows.

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Analysis of Compound Open Channel Flow Using Large Eddy Simulation (LES) (Large Eddy Simulation (LES)을 이용한 복단면 개수로 흐름 분석)

  • Lee, Du Han
    • Ecology and Resilient Infrastructure
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    • v.4 no.1
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    • pp.54-62
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    • 2017
  • This study investigated compound open channel flow using OpenFOAM Large Eddy Simulation (LES). Large eddy simulations were carried out by solving the filtered continuity and momentum equations numerically. One equation LES and non-uniform grid were applied to capture the anisotropic turbulence and secondary flow near the wall. The results of large eddy simulations of turbulent flow in a compound open channel with deep and shallow flood plain depths are presented. These LESs are validated with experimental data, resulting in a good agreement between measured and calculated data. The role of anisotropic turbulence in generating secondary currents is illustrated.

COARSE GRID LARGE-EDDY SIMULATION OF FLOW OVER A HEAVY VEHICLE (화물차 주위 유동의 성긴 격자 큰에디모사)

  • Lee, S.;Kim, M.;You, D.;Kim, J.J.;Lee, S.J.
    • Journal of computational fluids engineering
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    • v.21 no.1
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    • pp.30-35
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    • 2016
  • In order to investigate effects of grid resolution on large-eddy simulation of flow over a heavy vehicle, large-eddy simulations over the vehicle with coarse grid and fine grid are conducted. In addition, comparison of drag coefficients with the experimental data obtained by a wind tunnel experiment is conducted. Both of the drag coefficients of coarse grid and fine grid large-eddy simulation show good agreement with the experimental data. Flow fields obtained by the coarse and the fine grid large-eddy simulation are compared in the vehicle frontal-face region, the vehicle rear wheel region, and the vehicle base region. Coarse grid large-eddy simulation shows good agreement with the fine grid large-eddy simulation in the vehicle front face region and the vehicle rear wheel region, since the flow over the present vehicle is dominated by flow separation which is geometrically pre-determined, not by the skin friction which is known to be sensitive to grid resolution.

Flow Analysis in the Tip Clearance of Axial Flow Rotor Using Finite-Element Large-Eddy Simulation Method (유한요소 LES법에 의한 축류 회전차 팁 틈새의 유동해석)

  • Lee, Myeong-Ho
    • Journal of Advanced Marine Engineering and Technology
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    • v.33 no.5
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    • pp.686-695
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    • 2009
  • Flow characteristics in linear axial cascade have been studied using large eddy simulation(LES) based on finite element method(FEM) to investigate details of the leakage flow in the tip clearance of axial flow rotor. STAR-CD(FVM) and PAT-Flow(FEM) have been adopted to solve the Navier-Stokes equations for the simulation of the unsteady turbulent flow. Numerical results from the present study have been compared with the existing experimental results to investigate a tip clearance effect on velocity profile and static pressure distribution on blade surface at various spanwise positions. Both simulation results agree well with the experimental data. However, it has been shown that the results of finite-element large-eddy simulation agree better with experimental data than $k-{\varepsilon}$ turbulent model based on finite volume method regarding the tip vortex geometry and static pressure distribution at the center of the tip vortex core. As a result of this study, it is shown that finite-element large-eddy simulation method can predict more exactly on the tip leakage vortex flow and behind flow field.

Visualization of Unsteady Fluid Flows by Using Large Eddy Simulation

  • Kobayashi, Toshio;Taniguchi, Nobuyuki
    • Journal of Mechanical Science and Technology
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    • v.15 no.12
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    • pp.1750-1756
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    • 2001
  • Three-dimensional and unsteady flow analysis is a practical target of high performance computation. As recently advances of computers, a numerical prediction by the large eddy simulation (LES) are introduced and evaluated for various engineering problems. Its advanced methods for the complex turbulent flows are discussed by several examples applied for aerodynamic designs, analysis of fluid flow mechanisms and their interaction to complex phenomena. These results of time-dependent and three-dimensional phenomena are visualized by interactive graphics and animations.

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Large Eddy Simulation of Swirling Turbulent Flows in a Annular Combustor (환형연소기의 스월난류유동장에 대한 Large Eddy Simulation)

  • Kim, Jong-Chan;Sung, Hong-Gye;Cha, Bong-Jun;Yang, Gye-Byeung
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.67-70
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    • 2008
  • Production and dissipation of turbulent structure in a swirl stabilized combustor was investigated using three-dimensional Large Eddy Simulation analysis. The combustor of concern is the LM6000, lean premixed dry low-NOx annular combustor, developed by GEAE. Inlet condition was based on experimental data. Strong vortex breakdown in main stream, vortex ring proceeding downstream, and the turbulent structure periodically oscillating have been observed. Reasonable agreement was obtained by comparison of the results with experiments and previous LES studies.

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On the Spectral Eddy Viscosity in Isotropic Turbulence

  • Park Noma;Yoo Jung Yu;Choi Haecheon
    • 한국전산유체공학회:학술대회논문집
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    • pp.105-106
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    • 2003
  • The spectral eddy viscosity model is investigated through the large eddy simulation of the decaying and forced isotropic turbulence. It is shown that the widely accepted 'plateau and cusp' model overpredicts resolved kinetic energy due to the amplification of energy at intermediate wavenumbers. Whereas, the simple plateau model reproduces a correct energy spectrum. This result overshadows a priori tests based on the filtered DNS or experimental data. An alternative method for the validation of subgrid-scale model is discussed.

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Dynamic Large Eddy Simulation of the Vortex Breakdown of Swirling Flow using MPI Parallel Technique (Dynamic Large Eddy Simulation과 MPI병렬 계산 기법을 이용한 스월 유동에서의 Vortex Breakdown에 관한 연구)

  • Sung Hong Gye
    • Journal of computational fluids engineering
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    • v.6 no.1
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    • pp.31-39
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    • 2001
  • 연소실 안으로 분출되는 스월 유동의 vortex breakdown mechanism에 대한 연구를 하였다. 3차원 유한 체적기법과 Runge-Kutta 시간 적분법이 적용되었으며, 난류모델은 dynamic large eddy simulation (DLES)이 적용되었다. 계산 시간의 효율성과 기억용량을 효과적으로 사용하기 위하여 message passing interface (MPI) 병렬계산 기법이 적용되었다. 스월 난류 유동에 있어서 vortex breakdown 거동을 가시적으로 표착 하였는데, 이는 스월 유동에 의한 난류 응력 증대, 난류 생성/소산율 증대 및 혼합율 증대에 대한 실험적 근거를 뒷받침하는 매우 중요한 결과이다. 또한 평균 속도와 난류 운동에너지에 대한 계산 결과도 실험 결과와 비교하였다.

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Large Eddy Simulation of a Lifted Methane/Air Flame using FGM-based Multi-Environment PDF Approach (FGM기반 Multi-Environment PDF 모델을 이용한 메탄/공기 부상화염장의 Large Eddy Simulation)

  • Kim, Namsu;Kim, Jaehyun;Kim, Yongmo
    • 한국연소학회:학술대회논문집
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    • pp.265-266
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    • 2015
  • The multi-environment PDF model coupled with flamelet generated manifolds(FGM) has been developed for a large eddy simulation of turbulent partially premixed lifted flame. This approach has a capability to realistically account for the transport and evolution of probability density function for mixture fraction and progress variable with the manageable computational burden. Using the tabulated chemistry, it is possible to track radical distributions which is important to predict autoignition process with the vitiated coflow environment. Numerical results indicate that the present yields the good agreement with experimental data in terms of mixture fraction, temperature, and species mass fractions.

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