• 제목/요약/키워드: Subgrid scale stress

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

  • 김택근;박노마;유정열
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2004년도 춘계학술대회
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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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후향계단 DDES 해석의 길이척도 영향 분석 (EFFECT OF LENGTH-SCALE IN DDES FOR BACKWARD-FACING STEP FLOW)

  • 이충연;사정환;박수형;이은석;이진익;이광섭
    • 한국전산유체공학회지
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    • 제17권4호
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    • pp.24-31
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    • 2012
  • Effects of the subgrid length-scale in the Delayed-Detached Eddy Simulation(DDES) are investigated based on the Spalart-Allmaras(S-A) and the k-$\omega$ Shear Stress Transport(SST) turbulence models. Driver & Seegmiller's experimental results are used to validate numerical results. Grid convergence with grid resolution and subgrid length-scale is investigated. The simulation results show that the volume method for the subgrid length-scale is more resistant to unfavorable effects of the grid size in the periodic direction than the maximum method. Using a sufficient grid resolution and an appropriate subgrid length-scale, both S-A based DDES and SST based DDES methods can provide a good correlation with the experimental data.

난류 파이프 유동에서의 레이놀즈 수 영향: Part I. 평균 유동장 및 저차 난류통계치 (REYNOLDS NUMBER EFFECTS ON TURBULENT PIPE FLOW PART I. MEAN FLOW FIELD AND LOW-ORDER STATISTICS)

  • 강창우;양경수
    • 한국전산유체공학회지
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    • 제16권4호
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    • pp.28-38
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    • 2011
  • Large eddy simulation(LES) of fully developed turbulent pipe flow has been performed to investigate the effect of Reynolds number on the flow field at $Re_{\tau}$=180, 395, 590 based on friction velocity and pipe radius. A dynamic subgrid-scale model for the turbulent subgrid-scale stresses was employed to close the governing equations. The mean flow properties, mean velocity profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The Reynolds number effects were observed in the mean velocity profile, root-mean-square of velocity fluctuations, Reynolds shear stress and turbulent viscosity.

VIC 방법을 사용한 2차원 날개의 LES 해석 (Large Eddy Simulation for a 2-D hydrofoil using VIC(Vortex-In-Cell) method)

  • 김명수;김유철;서정천
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2011년 춘계학술대회논문집
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    • pp.407-413
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    • 2011
  • VIC (Vortex-In-Cell) method for viscous incompressible flow is presented to simulate the wake behind a modified NACA16 foil. With uniform rectangular grid, the velocity in field is calculated using streamfunction from vorticity field by solving the Poisson equation in which FFT(Fast Fourier Transform) is combined with 2nd order finite difference scheme. Here, LES(Large Eddy Simulation) with Smagorinsky model is applied for turbulence calculation. Effective viscosity is formulated using magnitude of strain tensor(or vorticity). Then the turbulent diffusion as well as viscous diffusion becomes particle strength exchange(PSE) with averaged eddy viscosity. The well-established panel method is combined to obtain the irrotational velocity and to apply the no-penetration boundary condition on the body panel. And wall diffusion is used for no-slip condition numerical results of turbulent stresses are compared with experimental results (Bourgoyne, 2003). Before comparing process, LES(Large Eddy Simulation) SGS(Subgrid scale) stress is transformed Reynolds averaged stress (Winckelmans, 2001).

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난류 파이프 유동에서의 레이놀즈 수 영향: Part II. 순간유동장, 고차 난류통계치 및 난류수지 (REYNOLDS NUMBER EFFECTS ON TURBULENT PIPE FLOW PART II. INSTANTANEOUS FLOW FIELD,HIGHER-ORDER STATISTICS AND TURBULENT BUDGETS)

  • 강창우;양경수
    • 한국전산유체공학회지
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    • 제16권4호
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    • pp.100-109
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    • 2011
  • Large eddy simulation(LES) of fully developed turbulent pipe flow has been performed to investigate the effect of Reynolds number on the flow field at $Re_{\tau}$=180, 395, 590 based on friction velocity and pipe radius. A dynamic subgrid-scale model for the turbulent subgrid-scale stresses was employed to close the governing equations. The mean flow properties, mean velocity profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The Reynolds number effects were observed in the higher-order statistics(Skewness and Flatness factor). Furthermore, the budgets of the Reynolds stresses and turbulent kinetic energy were computed and analyzed to elucidate the effect of Reynolds number on the turbulent structures.

큰 에디 모사 기법을 이용한 초기 천이 경계층 유동 및 방사 소음 해석 (A study on the early stage of a transitional boundary layer and far field noise using a large eddy simulation technique)

  • 최명렬;최해천;강신형
    • 대한기계학회논문집B
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    • 제21권6호
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    • pp.779-792
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    • 1997
  • Flow characteristics are numerically investigated when a packet of waves consisting of a Tollmien-Schlichting wave and a pair of Squire waves evolves in a flat-plate laminar boundary layer using a large eddy simulation with a dynamic subgrid-scale model. Characteristics of early stage transitional boundary layer flow such as the .LAMBDA. vortex, variation of the skin friction and backscatter are predicted. Smagorinsky constants and the eddy viscosity obtained from the dynamic subgrid-scale model significantly change as the flow evolves. Far Field noise radiated from the transitional boundary layer shows the dipole and quadrupole characteristics owing to the wall shear stress and the Reynolds stresses, respectively.

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

  • 박노마;유정열;최해천
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2002년도 학술대회지
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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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LES에서 중심 및 상류 컴팩트 차분기법의 적합성에 관하여 (I) - 수치 실험 - (On the Suitability of Centered and Upwind-Biased Compact Difference Schemes for Large Eddy Smulation (I) - Numerical Test -)

  • 박노마;유정열;최해천
    • 대한기계학회논문집B
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    • 제27권7호
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    • pp.973-983
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    • 2003
  • The suitability of high-order accurate, centered and upwind-biased compact difference schemes is evaluated for large eddy simulation of turbulent flow. Two turbulent flows are considered: turbulent channel flow at Re = 23000 and flow over a circular cylinder at Re = 3900. The effects of numerical dissipation on the finite differencing and aliasing errors and the subgrid-scale stress are investigated. It is shown through the simulations that compact upwind schemes are not suitable for LES, whereas the fourth order-compact centered scheme is a good candidate for LES provided that proper dealiasing of nonlinear terms is performed. The classical issue on the aliasing error and the treatment of nonlinear terms is revisited with compact difference schemes.

LES를 이용한 직사각형 개수로 난류흐름의 조직구조 분석 (Analysis of Coherent Structure of Turbulent Flows in the Rectangular Open-Channel Using LES)

  • 반채웅;최성욱
    • 대한토목학회논문집
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    • 제34권5호
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    • pp.1435-1442
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    • 2014
  • 본 연구에서는 OpenFOAM에서 제공하는 소스코드를 이용하여 매끄러운 하상의 직사각형 개수로 흐름에 대해 수치모의를 수행하였다. 난류 해석을 위해 LES를 수행하였는데, 비등방성 잔여 응력항을 모델링하기 위해서 Germano et al. (1991)이 제시한 Dynamic Subgrid-scale 모형을 이용하였다. 조직구조를 분석하기 위하여 Lu and Willmarth (1973)가 제시한 uw 사분면기법을 이용하여 순간레이놀즈 응력이 레이놀즈 응력에 미치는 영향을 기여율과 시간비로 나누어 분석하였다. LES 모의 결과를 토대로 기존 실험 및 DNS 모의 결과와 비교하고 분석하였다. 매끈한 하상을 가진 개수로 흐름에서 완충층 이후의 구간에서 분출현상이 쓸기현상에 비해 레이놀즈 응력의 양의 생성에 기여하는 바가 크지만, 분출현상에 비해 쓸기현상의 발생빈도가 큰 것으로 확인되었다.

대규모 와 모사에 의한 3차원 소형축류홴의 운전부하에 따른 난류유동 특성치 고찰 (An Investigation on Turbulent Flow Characteristics According to the Operating Loads of Three-Dimensional Small-Size Axial Fan by Large Eddy Simulation)

  • 김장권;오석형
    • 동력기계공학회지
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    • 제20권1호
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    • pp.50-56
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    • 2016
  • This paper handled an investigation on the turbulent flow characteristics of three-dimensional small-size axial fan(SSAF) according to operating loads. Also, it was carried out by unsteady-state, incompressible and three-dimensional large eddy simulation(LES). The downstream flow type of SSAF is changed from axial flow to radial flow around the beginning of stall region at the aerodynamic performance curve. Axial mean velocity component largely grows around blade tip at the operating point of A to D, but transverse and vertical mean velocity components as well as Reynolds shear stresses highly develop around blade tip at the operating point of E to H. On the other hand, the peak value of turbulent kinetic energy developed around blade tip shows the highest at the operating point of E.