• 제목/요약/키워드: Dynamic Subgrid Scale Model

검색결과 27건 처리시간 0.026초

Effect of Dynamic SGS Model in a Kerosene-LOx Swirl Injector under Supercritical Condition

  • Heo, Jun-Young;Hong, Ji-Seok;Sung, Hong-Gye
    • International Journal of Aeronautical and Space Sciences
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    • 제16권2호
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    • pp.254-263
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    • 2015
  • In this study, numerical simulations are carried out to investigate the dynamic SGS model effects in a Kerosene-LOx coaxial swirl injector under high pressure conditions. The turbulent model is based on large-eddy simulation (LES) with real-fluid transport and thermodynamics. To assess the effect of the dynamic subgrid-scale (SGS) model, the dynamic SGS model is compared with that of the algebraic SGS model. In a swirl injector under supercritical pressure, the characteristics of temporal pressure fluctuation and power spectral density (PSD) present comparable discrepancies dependant on the SGS models, which affect the mixing characteristics. Mixing efficiency and the probability density (PDF) function are conducted for a statistical description of the turbulent flow fields according to the SGS models. The back-scattering of turbulent kinetic energy is estimated in terms of the film thickness of the swirl injector.

Dynamic Sub-grid 모델을 이용한 G 방정식에 의한 보염기 주위의 난류 예혼합 연소에 관한 대 와동 모사 (Large Eddy Simulation of Turbulent Premixed Combustion Flow around Bluff Body based on the G-equation with Dynamic sub-grid model)

  • 박남섭;고상철
    • Journal of Advanced Marine Engineering and Technology
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    • 제34권8호
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    • pp.1084-1093
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    • 2010
  • 화염 전파 특성을 나타내는 G 방정식에 기초한 Sub-grid Scale연소 모델을 이용하여 보염기 주위의 난류 예혼합 연소 해석에 관한 대 와동 모사를 수행하였다. Dynamic SGS 모델이 G방정식에 도입되었으며, 삼각형의 보염기 배면의 예혼합 연소 유동에 의해 검증되었다. 해석결과는 실험결과와의 비교를 통해 속도와 온도분포를 잘 예측하고 있음을 확인하였다.

동적혼성 모델을 이용한 난류채널의 온도장 해석 (On the Large Eddy Simulation of Temperature Field Using Dynamic Mixed Model in a Turbulent Channel)

  • 이건호;나양
    • 대한기계학회논문집B
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    • 제28권10호
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    • pp.1255-1263
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    • 2004
  • An a priori test has been conducted for the dynamic mixed model which was generalized for the prediction of passive scalar field in a turbulent channel flow The results from a priori tests indicated that dynamic mixed model is capable of predicting both subgrid-scale heat flux and dissipation rather accurately. The success is attributed to the explicitly calculated resolved term incorporated into the model. The actual test of the model in a LES a posteriori showed that dynamic mixed model is superior to the widely used dynamic Smagorinsky model in the prediction of temperature statistics.

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.

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.

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

  • Huang, Shenghong;Li, Q.S.
    • Wind and Structures
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    • 제13권6호
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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.

강풍피해 위험성 평가를 위한 건물군 주위 유동해석 (Numerical simulation of turbulent flow around a building complex for development of risk assessment technique for windstorm hazards)

  • 최춘범;양경수;이승수;함희정
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2007년도 춘계학술대회B
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    • pp.2737-2742
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    • 2007
  • Strong wind flow around a building complex was numerically studied by LES. The original motivation of this work stemmed from the efforts to develop a risk assessment technique for windstorm hazards. Lagrangian-averaged scale-invariant dynamic subgrid-scale model was used for turbulence modeling, and a log-law-based wall model was employed on all the solid surfaces including the ground and the surface of buildings to replace the no-slip condition. The shape of buildings was implemented on the Cartesian grid system by an immersed boundary method. Key flow quantities for the risk assessment such as mean and RMS values of pressure on the surface of the selected buildings are presented. In addition, characteristics of the velocity field at some selected locations vital to safety of human beings is also reported.

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LES를 이용한 축류 터빈 경계층 천이에 대한 수치해석 (Large Eddy Simulation of Boundary Layer Transition on the Turbine Blade)

  • 진병주;박노마;유정열
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집E
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    • pp.392-397
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    • 2001
  • A numerical study is performed to investigate the interaction between subsonic axial turbine blade boundary layer and periodically oncoming rotor induced wakes. An implicit scheme for solving the compressible Navier-Stokes equation is developed, which adopts a 4th-order compact difference for spatial discretiztion, a 2nd order Crank-Nicolson scheme for temporal discretization and the dynamic eddy viscosity model as the subgrid scale model. The efficiency and the accuracy of the proposed method are verified by applying to some benchmark problems such as laminar cylinder flow, laminar airfoil cascade flow and a transitional flat plate boundary layer flow. Computational results show good agreements with previous experimental and numerical results. Finally, flow through a stator cascade is simulated at $Re = 7.5{\times}10^5$ without free-stream turbulence intensity. The velocity fields and skin friction coefficients in the transitional region show similar trends with previous boundary layer natural transition.

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LES를 이용한 NACA0018 에어포일 주위의 유동 및 이산소음계산 (Flow and Noise Characteristics of NACA0018 by Large-Eddy Simulation)

  • 김휘중;이승배
    • 유체기계공업학회:학술대회논문집
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    • 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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    • pp.433-438
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    • 2002
  • The flow field around a symmetrical airfoil in a uniform flow under the generation of noise was numerically studied and compared with experimental datum. The numerical simulation was carried out by LES which employs a deductive dynamic model as subgrid-scale model. The result of an attack angle of $6^{\circ}$ indicate that the discrete frequency noise is generated when the separated laminar flow reattaches near the trailing edge of the pressure side and the turbulent boundary layer is formed over the suction side of the airfoil near the trailing edge. The periodic behavior of vortex formation was observed around the trailing edge and it persists further downstream in the wake. The frequency of the vortex formation in the wake was consistent with that of the discrete frequency noise.

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속도미분비대칭도를 고려한 초기난류 속도장 생성방법 연구 (A Study on the Generation of Initial Turbulent Velocity Field with Non-zero Velocity Derivative Skewness)

  • 고범용;박승오
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2002년도 학술대회지
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    • pp.819-822
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    • 2002
  • It is necessary for the numerical simulation of 3-dimensional incompressible isotropic decaying turbulence to construct 3-dimensional initial velocity field which resembles the fully developed turbulence. Although the previous velocity field generation method proposed by Rogallo(1981) satisfies continuity equation and 3-dimensional energy spectrum, it has limitation, as indicated in his paper, that it does not produce the higher velocity moments(e. g. velocity derivative skewness) characteristic of real turbulence. In this study, a new velocity field generation method which is able to control velocity derivative skewness of initial velocity field is proposed. Brief descriptions of the new method and a few parameters which is used to control velocity derivative skewness are given. A large eddy simulation(LES) of isotropic decaying turbulence using dynamic subgrid-scale model is carried out to evaluate the performance of the initial velocity field generated by the new method. It was shown that the resolved turbulent kinetic energy decay curve and the resolved enstrophy decay curve from the initial field of new method were more realistic than those from the initial field of Rogallo's method. It was found that the dynamic model coefficient from the former was initially half the stationary value and experienced relatively short transition period, though that from the latter was initially zero and experienced relatively longer transition period.

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