• Title/Summary/Keyword: 비선형 난류모델

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Towards Prediction of Unsteady Turbulent Flow over a Square Cylinder using Two-Equation Turbulence Models (2-방정식 난류모델을 이용한 정사각주 주위의 비정상 난류유동의 예측)

  • Lee Sangsan
    • Journal of computational fluids engineering
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    • v.1 no.1
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    • pp.47-54
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    • 1996
  • 비유선형 물체 주위의 유동은 정체유동, 경계층 박리 및 재부착, 주기적 와열의 생성등의 복잡한 유동현상이 공존한다. 이와 같은 유동의 2-방정식 난류모델을 이용한 정확한 예측은 일반적으로 불가능 하다고 인식되어 왔으나, 본 연구에서는 기존의 비교적 단순한 난류모델을 활용한 정사각주 주위의 비정상 난류유동의 예측 가능성을 체계적으로 규명하였다. 적절한 난류모델의 선정과 더불어 시간 정확도, 공간 정확도 및 대류항 처리법 등이 해석의 결과에 미치는 영향을 살펴 보았다. 기존의 표준 κ-ε모델은 정체점 주위에서 난류생성항의 과도한 예측으로 말미암아 재부착 및 와열생성의 정확한 예측이 불가능 하였으나, RNG κ-ε 모델을 사용한 경우 이와 같은 현상을 제거 할 수 있었다. 그러나 이 경우에도 예측의 정확도가 시간 증분, 격자의 크기 및 대류항 처리법 등에 영향을 받았으며, 특별히 대류항 처리법에 따라 상당히 민감하게 변하는 것을 알 수 있었다.

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Numerical Simulation of Turbulent Heat Transfer in a Channel with One Wavy Wall (파형벽면이 있는 채널내의 난류열전달에 대한 수치해석)

  • Park Tae-Seon
    • Journal of the Korean Society of Propulsion Engineers
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    • v.9 no.3
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    • pp.49-59
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    • 2005
  • Turbulent heat transfer over a fully-developed wavy channel is investigated by a turbulence model. The nonlinear k- f - f$_{ model of Park et at.[1] is slightly modified and their explicit algebraic heat flux model is employed. The Reynolds number is fixed at Re$_{b}$=6760 and the wave configuration is varied in the range of 0 $\leq$ $\alpha$/$\lambda$$\leq$0.15 and 0.25 $\leq$A/H$\leq$4.0. In order to verify model performances, a large eddy simulation is performed for the selected cases. The model performance is shown to be generally satisfactory. By using k- $\varepsilon$ - f$_{ model, the enhancement of heat transfer and the characteristics of turbulent flow in wavy wall are investigated. Finally, the influence of wavy configuration on heat transfer is scrutinized.

Prediction of Fully Developed Turbulent Flow in a Square Duct with Nonlinear Low-Reynolds-Number κ-ε Models (비선형 저레이놀즈수 κ-ε 난류모델에 따른 정사각형 덕트내 완전 발달된 난류유동 예측)

  • Myong, Hyon-Kook,
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.6
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    • pp.821-827
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    • 2003
  • Fully developed turbulent flow in a square duct is numerically predicted with two nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ models. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in detail with each other. It is found that the nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ model adopted in a commercial code is unable to predict accurately duct flows involving turbulence-driven secondary motion with the prediction level of secondary flows one order less than that of the experiment.

Evaluation of Nonlinear κ-ε Models on Prediction Performance of Turbulence-Driven Secondary Flows (난류에 의해 야기되는 이차유동 예측성능에 대한 비선형 κ-ε 난류모델의 평가)

  • Myong, Hyon-Kook
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.8
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    • pp.1150-1157
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    • 2003
  • Nonlinear relationship between Reynolds stresses and the rate of strain of nonlinear k-$\varepsilon$models is evaluated theoretically by using the boundary layer assumptions against the turbulence-driven secondary flows in noncircular ducts and then their prediction performance is validated numerically through the application to the fully developed turbulent flow in a square duct. Typical predicted quantities such as mean axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared with available experimental data. The nonlinear k-$\varepsilon$ model adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.

Simulation of Turbulent Flow in a Square Duct with Nonlinear k-$\varepsilon$ Models (비선형 k-$\varepsilon$ 난류모델에 따른 정사각형 덕트내 난류유동 수치해석(8권1호 게재논문중 그림정정))

  • Myong Hyon Kook
    • Journal of computational fluids engineering
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    • v.8 no.2
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    • pp.57-63
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    • 2003
  • Two nonlinear κ-ε models with the wall function method are applied to the fully developed turbulent flow in a square duct. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in details both qualitatively and quantitatively with each other. A nonlinear κ-ε model with the wall function method capable of predicting accurately duct flows involving turbulence-driven secondary motion is presented in the present paper. The nonlinear κ-ε model of Shih et al.[1] adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.

Simulation of Turbulent Flow in a Triangular Subchannel of a Bare Rod Bundle with Nonlinear k-$\varepsilon$ Models (비선형 k-$\varepsilon$ 난류모델에 의한 봉다발의 삼각형 부수로내 난류유동 수치해석)

  • Myong Hyon Kook
    • Journal of computational fluids engineering
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    • v.8 no.2
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    • pp.8-15
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    • 2003
  • Three nonlinear κ-ε models with the wall function method are applied to the fully developed turbulent flow in a triangular subchannel of a bare rod bundle. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and wall shear stress are compared in details both qualitatively and quantitatively with both each other and experimental data. The nonlinear κ-ε models by Speziale[1] and Myong and Kasagi[2] are found to be capable of predicting accurately noncircular duct flows involving turbulence-driven secondary motion. The nonlinear κ-ε model by Shih et aL.[3] adopted in a commercial code is found to be unable to predict accurately noncircular flows with the prediction level of secondary flows one order less than that of the experiment.

Prediction of Turbulent Flow in a Square Duct with Nonlinear ${\kappa}-{\epsilon}$ Models (비선형 ${\kappa}-{\epsilon}$ 난류모델에 따른 정사각형 덕트내 난류유동 예측)

  • Myong, Hyon-Kook
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1980-1985
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    • 2003
  • Two nonlinear ${\kappa}-{\epsilon}$ models with the wall function method are applied to the fully developed turbulent flow in a square duct. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in details both qualitatively and quantitatively with each other. A nonlinear ${\kappa}-{\epsilon}$ model with the wall function method capable of predicting accurately duct flows involving turbulence-driven secondary motion is presented in the present paper. The nonlinear ${\kappa}-{\epsilon}$ model adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.

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Simulation of Turbulent Flow in a Square Duct with Nonlinear k-$\varepsilon$ Models (비선형 k-$\varepsilon$ 난류모델에 따른 정사각형 덕트내 난류유동 수치해석)

  • Myong Hyon Kook
    • Journal of computational fluids engineering
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    • v.8 no.1
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    • pp.23-29
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    • 2003
  • Two nonlinear κ-ε models with the wall function method are applied to the fully developed turbulent flow in a square duct. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in details both qualitatively and quantitatively with each other. A nonlinear κ-ε model with the wall function method capable of predicting accurately duct flows involving turbulence-driven secondary motion is presented in the present paper. The nonlinear κ-ε model of Shih et al.[1] adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.

A Study on the Design of Coal Gasification Unit using Computational Fluid Dynamics (전산유체역학을 이용한 분류층 석탄가스화기 설계연구)

  • 이선경;나혜령;장동순;정진도;지평심
    • Journal of Energy Engineering
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    • v.4 no.1
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    • pp.23-30
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    • 1995
  • 분류층 가스화기 설계를 위한 일차연구로서 가스화기 종횡비, 주입方法, 선회강도 및 주입속도 등에 따른 비반응 난류장 특성을 수치해석적 방법에 의해 파악하였다. 수치해석은 검사체적에 기초한 Patankar의 유한차분방법을 이용하였으며 압력과 속도의 연계문제는 SIMPLEC 알고리즘을, 레이놀즈 전단력은 K- 난류모델을 사용하였다. 입자궤적 계산은 공기역학적 향력만을 고려하였으며 비선형적인 공기저항력에 의한 난류변동상관모델은 고려치 않았다. 이차공기 주입방법(parallell injection과 nonparallel 3$0^{\circ}C$ imjection)에 따른 수치해석을 수행하여 Ar tracer의 질량분율 및 기타 속도에 대한 實驗資料와 비교하여 만족할 만한 結果를 얻었다. 나아가서 假想的인 가스화기 모델을 대상으로 가스화기의 종횡비, 선회강도, 주입속도 및 주입각 등에 따른 와류 形成 위치 등을 포함한 유동장 특성 및 입도에 따른 궤적분석을 시도하였다.

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