• 제목/요약/키워드: Standard k-$\varepsilon$

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수정된 Extendel $k-\varepsilon$ 난류모델을 사용한 $90^{\circ}$곡관 내의 난류유동에 관한 수치해석적 연구 (Numerical Computations of Turbulent Flow in a $90^{\circ}$ Curved Duct Using a Modified Extended $k-\varepsilon$ Turbulence Model)

  • 정수진;김태훈;조진호
    • 한국자동차공학회논문집
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    • 제4권3호
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    • pp.139-146
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    • 1996
  • An extended $k-\varepsilon$ tuebulence model modified by considering the streamline curvature effect and standard $k-\varepsilon$ turbulence model have been applied for three dimensional analysis of turbulece flow in a $90^{\circ}$ curved duct. By comparision of the results with the experimental data, the modified extended $k-\varepsilon$ model gave closer agreement with experimental data than the results from standard $k-\varepsilon$ model owing to an extra time scale of the production rate and parameter describing effects of streamline curvature included in the dissipation rate equation.

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난류모델에 따른 건물주위의 유동 예측 (A Prediction of the Flow Characteristics around Buildings with the Turbulent Models)

  • 이승호;여재현;허남건;최창근
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2008년도 춘계학술대회논문집
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    • pp.168-171
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    • 2008
  • In the present study, turbulent flows around cubic and L-shape buildings were simulated numerically. Standard ${\kappa}$-$\varepsilon$, RNG ${\kappa}$-$\varepsilon$, LES turbulence models were adopted for the present simulation. The wind pressure coefficients from these results were compared with the available experimental data. The result of RNG ${\kappa}$-$\varepsilon$ and LES turbulent models gave better prediction than that of standard ${\kappa}$-$\varepsilon$ turbulent model which is widely used in the turbulent flow simulation.

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NOTE ON CONTACT STRUCTURE AND SYMPLECTIC STRUCTURE

  • Cho, Mi-Sung;Cho, Yong-Seung
    • 대한수학회보
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    • 제37권1호
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    • pp.181-189
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    • 2000
  • Let (X, J) be a closed, connected almost complex four-manifold. Let $X_1$ be the complement of an open disc in X and let ${\varepsilon}_1$be the contact structure on the boundary ${\varepsilon}X_1$ which is compatible with a symplectic structure on $X_1$, Then we show that (X, J) is symplectic if and only if the contact structure ${\varepsilon}_1$ on ${\varepsilon}X_1$ is isomorphic to the standard contact structure on the 3-sphere $S^3$ and ${\varepsilon}X_1$is J-concave. Also we show that there is a contact structure ${\varepsilon}_0\ on\ S^2\times\ S^1$which is not strongly symplectically fillable but symplectically fillable, and that $(S^2{\times}S^1,\;{\varepsilon})$ has infinitely many non-diffeomorphic minimal fillings whose restrictions on$\S^2\times\ S^1$are ${\sigma}$ where ${\sigma}$ is the restriction of the standard symplectic structure on $S^2{\times}D^2$.

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Numerical simulation of flow past 2D hill and valley

  • Chung, Jaeyong;Bienkiewicz, Bogusz
    • Wind and Structures
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    • 제7권1호
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    • pp.1-12
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    • 2004
  • Numerical simulation of flow past two-dimensional hill and valley is presented. Application of three turbulence models - the standard and modified (Kato-Launder) $k-{\varepsilon}$ models and standard $k-{\omega}$ model - is discussed. The computational methodology is briefly described. The mean velocity and turbulence intensity profiles, obtained from numerical simulations of flow past the hill, are compared with the experimental data acquired in a boundary-layer wind tunnel at Colorado State University. The mean velocity, turbulence kinetic energy and Reynolds shear stress profiles from numerical simulations of flow past the valley are compared with published experimental data. Overall, the results of simulations employing the standard $k-{\varepsilon}$ model were found to be in a better agreement with the experimental data than those obtained using the modified $k-{\varepsilon}$ model and the $k-{\omega}$ model.

점탄성 유체의 난류 해석을 위한 수정된 $k-{\varepsilon}$ 난류모델 개발 및 혈류역학에의 적용 (DEVELOPMENT OF A MODIFIED $k-{\varepsilon}$ TURBULENCE MODEL FOR VISCO-ELASTIC FLUID AND ITS APPLICATION TO HEMODYNAMICS)

  • 노경철;유홍선
    • 한국전산유체공학회지
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    • 제15권4호
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    • pp.1-8
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    • 2010
  • This article describes the numerical investigation of turbulent blood flow in the stenosed artery bifurcation under periodic acceleration of the human body. Numerical analyses for turbulent blood flow were performed with different magnitude of periodic accelerations using a modified turbulence model which was considering drag reduction of non-Newtonian fluid. The blood was considered to be a non-Newtonian fluid which was based on the power-law viscosity. In order to validate the modified $k-{\varepsilon}$ model, numerical simulations were compared with the standard $k-{\varepsilon}$ model and the Malin's low Reynolds number turbulence model for power-law fluid. As results, the modified $k-{\varepsilon}$ model represents intermediate characteristics between laminar and standard $k-{\varepsilon}$ model, and the modified $k-{\varepsilon}$ model showed good agreements with Malin's verified power law model. Moreover, the computing time and computer resource of the modified $k-{\varepsilon}$ model were reduced about one third than low Reynolds number model including Malin's model.

축대칭 선회난류의 수치해석에 의한 비등방 k - ${\epsilon}$ 난류모델의 評價 (Evaluation of the Anisotropic k - ${\epsilon}$ Turbulence Model by the Numerical Analysis of Axisymmetric Swirling Turbulent Flow)

  • 이연원
    • Journal of Advanced Marine Engineering and Technology
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    • 제20권5호
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    • pp.39-44
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    • 1996
  • To overcome weak poinks of the standard k-${\varepsilon}$ turbulence model when applied to complex turbulent flows, various modified models were proposed. But their effects are confined to special flow fields. They have still some problems. Recently, an anisotropic k-${\varepsilon}$ turbulence model was also proposed to solve the drawback of the standard k-${\varepsilon}$ turbulence model. This study is concentrated on the evaluation of the anisotropic k-${\varepsilon}$ turbulence model by the analysis of axisymmetric swirling turbulent flow. Results show that the anisotropic k-${\varepsilon}$ turbulence model has scarecely the fundamentally physical mechanism of predicting the swirling structure of flow.

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Numerical method study of how buildings affect the flow characteristics of an urban canopy

  • Zhang, Ning;Jiang, Weimei;Hu, Fei
    • Wind and Structures
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    • 제7권3호
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    • pp.159-172
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    • 2004
  • The study of how buildings affect wind flow is an important part of the research being conducted on urban climate and urban air quality. NJU-UCFM, a standard $k-{\varepsilon}$ turbulence closure model, is presented and is used to simulate how the following affect wind flow characteristics: (1) an isolated building, (2) urban canyons, (3) an irregular shaped building cluster, and (4) a real urban neighborhood. The numerical results are compared with previous researchers' results and with wind tunnel experiment results. It is demonstrated that the geometries and the distribution of urban buildings affect airflow greatly, and some examples of this include a changing of the vortices behind buildings and a "channeling effect". Although the mean air flows are well simulated by the standard $k-{\varepsilon}$ models, it is important to pay attention to certain discrepancies when results from the standard $k-{\varepsilon}$ models are used in design or policy decisions: The standard $k-{\varepsilon}$ model may overestimate the turbulence energy near the frontal side of buildings, may underestimate the range of high turbulence energy in urban areas, and may omit some important information (such as the reverse air flows above the building roofs). In ideal inflow conditions, the effects of the heights of buildings may be underestimated, when compared with field observations.

3차원 튜브 뱅크 주위의 난류 유동장 및 열전달에 대한 수치 해석적 연구 (The Numerical Simulation of Flow Field and Heat Transfer around 3-D Tube Banks)

  • 박상길;김경원;유홍선;최영기
    • 설비공학논문집
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    • 제8권3호
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    • pp.375-385
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    • 1996
  • Turbulent flow and heat transfer characteristics around staggered tube banks were studied using the 3-D Navier-Stokes equations and energy equation governing a steady incompressible flow, which were reformulated in a non-orthogonal coordinate system with cartesian velocity components and discretized by the finite volume method with a non-staggered variable arrangement. The predicted turbulent kinetic energy using RNG $k-{\varepsilon}$ model was lower than that of standard $k-{\varepsilon}$ model but showed same result for mean flow field quantities. The prediction of the skin friction coefficient using RNG $k-{\varepsilon}$ model showed better trend with experimental data than standard $k-{\varepsilon}$ model result. The inclined flow showed higher velocity and skin friction coefficient than transverse flow because of extra strain rate ($\frac{{\partial}w}{{\partial}y}$). Also, this was why the inclined flow showed higher local heat transfer coefficient than the transverse flow.

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RNG k-$\varepsilon$ 난류모델을 이용한 유동박리 및 선회를 가지는 난류유동의 예측 (Prediction of Turbulent Flows with Separation and Swirl Using the RNG K-$\varepsilon$ Turbulence Model)

  • 김성구;오군섭;김용모;이창식
    • 한국자동차공학회논문집
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    • 제4권5호
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    • pp.119-129
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    • 1996
  • This study is concerned with the critical evaluation of predicative capability of a k-$\varepsilon$ turbulence model using the Renormalization Group(RNG) theory. The present numerical model for solution of the Navier-Stokes System is based on the modified PISO algorithms. Computations have been performed with the RNG-based K-$\varepsilon$ model for the two-dimensional flow over a backward-facing step, a confined coaxial jet, and a swirling flow in a swirl combustor. Numerical results are compared with experimental data in terms of mean flow velocities, turbulent kinetic energy, and turbulent stresses. Numerical results clearly indicate that the RNG-based K-$\varepsilon$ turbulence model shows a significant improvement over a standard K-$\varepsilon$ model in predicting the turbulent flows with flow separation and swirl.

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축류 회전차 익말단 틈새유동에 대한 수치해석(II) - 틈새변화 및 영각변화에 따른 누설와류의 변화 - (Numerical Analysis on the Blade Tip Clearance Flow in the Axial Rotor (II) - Variation of Leakage Vortex with Tip Clearance and Attack Angle -)

  • 노수혁;조강래
    • 대한기계학회논문집B
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    • 제23권9호
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    • pp.1106-1112
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    • 1999
  • Substantial losses behind axial flow rotor are generated by the wake, various vortices in the hub region and the tip leakage vortex in the tip region. Particularly, the leakage vortex formed near blade tip is one of the main causes of the reduction of performance, generation of noise and aerodynamic vibration in downstream. In this study, the three-dimensional flow fields in an axial flow rotor were calculated with varying tip clearance under various flow rates, and the numerical results were compared with experimental ones. The numerical technique was based on SIMPLE algorithm using standard $k-{\varepsilon}$ model(WFM) and Launder & Sharma's Low Reynolds Number $k-{\varepsilon}$ model(LRN). Through calculations, the effects of tip clearance and attack angle on the 3-dimensional flow fileds behind a rotor and leakage flow/vortex were investigated. The presence of tip leakage vortex, loci of vortex center and its behavior behind the rotor for various tip clearances and attack angles was described well by calculation.