• Title/Summary/Keyword: Realizable $k-{\varepsilon}$

검색결과 51건 처리시간 0.02초

Comparison of Turbulence Models for the Prediction of Wakes around VLCC Hull Forms

  • Kim, Wu-Joan;Kim, Do-Hyun;Van, Suak-Ho
    • Journal of Ship and Ocean Technology
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    • 제5권2호
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    • pp.27-48
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    • 2001
  • Turbulent flow calculations are performed for the two modern practical VLCCs with the sable forebody and the slightly different afterbody, i.e. KVLCC and KVLCC2. Three $\textsc{k}-\varepsilon$ turbulence models are tested to investigate the differences caused by the turbulence models. The calculated results around the two VLCC hull forms using O-O grid topology and profile-fitted surface meshes are compared to the measured data from towing tank experiment. The realizable $\textsc{k}-\varepsilon$model provided realistic wake distribution with hook-like shape, while the standard and RNG-based $\textsc{k}-\varepsilon$models failed. It is very encouraging to see that the CFD with relatively simple turbulence closure can tell the difference quantitatively as well as qualitatively for the two hull forms with stern frameline modification.

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축대칭체 주위 고 레이놀즈수 유동에 대한 수치해석 (Numerical Analysis of High-Reynolds-Number Flow around Axisymmetric Body)

  • 최정규;김형태
    • 대한조선학회논문집
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    • 제45권6호
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    • pp.631-636
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    • 2008
  • In this paper, numerical analysis based on the RANS equation and the Realizable ${\kappa}-{\varepsilon}$ turbulence model is carried out for flows around an axisymmetric body at three Reynolds numbers($1.22{\times}10^7$, $1.0{\times}10^8$, $1.5{\times}10^8$) and the numerical results are compared with experiments data. Computed velocity distributions agree well with experiments as the Reynolds number increases. Pressure distributions agree well with the results of the potential flow except the tail region but differ from experiments for the parallel middle body as well as tail region. Pressure gradients show a good agreement with those of potential flow and experiment except the tail region. Friction coefficients show that the numerical results generally are lower than the experimental results estimated from the measured velocity. The difference of friction coefficients between the calculation and the experiment increases with growing of a boundary layer.

원형 실린더 주위의 유동해석을 통한 URANS 난류 모델 성능 비교 (Evaluation of URANS Turbulence Models through the Prediction of the Flow around a Circular Cylinder)

  • 김민재;신지환;권래언;이건철
    • 한국군사과학기술학회지
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    • 제17권6호
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    • pp.861-867
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    • 2014
  • In the present study, the flow around a circular cylinder at $Re=3.6{\time}10^6$ is numerically simulated using URANS approach. The objective of this study is to evaluate the turbulence models(Realizable k-${\varepsilon}$, RNG k-${\varepsilon}$) through the prediction of the unsteady flow characteristics around the cylinder. The time-averaged drag coefficients and vortex shedding phenomenon in the wake region are compared to available experimental data and other numerical results. The simulation with Realizable k-${\varepsilon}$ model is found to be more dissipative due to large eddy viscosity predicted in the wake region while the simulation with RNG k-${\varepsilon}$ model predicts a complex vortex shedding phenomenon with more coherent structures realistically.

Wind pressures on different roof shapes of a finite height circular cylinder

  • Ozmen, Y.;Aksu, E.
    • Wind and Structures
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    • 제24권1호
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    • pp.25-41
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    • 2017
  • The effects of finite cylinder free end shape on the mean and fluctuating wind pressures were investigated experimentally and numerically by using three different roof shapes: flat, conical and hemispherical. The pressure distributions on the roofs and the side walls of the finite cylinders partially immersed in a simulated atmospheric boundary layer have been obtained for three different roof shapes. Realizable $k-{\varepsilon}$ turbulence model was used for numerical simulations. Change in roof shapes has caused significant differences on the pressure distributions. When compared the pressure distributions on the different roofs, it is seen from the results that hemispherical roof has the most critical pressure field among the others. It is found a good agreement between numerical and experimental results.

선박 워터제트 추진기 덕트 내부의 난류유동 해석에 관한 연구 (Computational study on turbulent flows inside the duct of marine waterjet propulsor)

  • 박일룡;김우전;안종우;김기섭
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2002년도 학술대회지
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    • pp.181-184
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    • 2002
  • CFD calculations are carried out to investigate the turbulent flow characteristics inside the duct of marine waterjet propulsors. The Reynolds-averaged Wavier-Stokes equations are solved using a finite-volume method. Standard $k-{\varepsilon}$ model and realizable $k-{\varepsilon}$ model are evaluated with an existing experimental data. Multi-block grid topology is adopted to describe the details of complex duct geometry. The present numerical methods are applied to the preliminary duct design of new waterjet propulsor system. Four different influx conditions are simulated to find out pressure and velocity distribution inside the intake duct. Attention is also paid upon the possible flow separation inside the waterjet duct. It is found that CFD tools can be used for the initial evaluation of inflow condition into the impeller of waterjet propulsor system.

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모형 램젯 연소기에서 액체제트의 다상유동 해석 (Multiphase Simulation of a Liquid Jet in a Lab-scale Ramjet Combustor)

  • 오정석;이원남;이종근
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2010년도 제35회 추계학술대회논문집
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    • pp.386-392
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    • 2010
  • 상용 전산유체해석 프로그램을 사용하여 오리피스형 분사기에서 수직분사 액체 제트의 다상유동을 해석하였다. 본 연구의 목적은 오리피스형 분사기 분무 특성을 이해하고 연소기 내부 위치에 따른 유동조건와 항력계수와의 관계식을 구하는 것이다. 수치해석 결과 모형 램젯 연소기에서 수직분사 유동해석은 난류점성모델인 Realizable $k-{\varepsilon}$ 모델과 다상유동모델인 DPM 모델이 유효함을 확인하였다. 또한 오리피스형 분사기에서 레이저 흡수법을 사용하여 측정한 실험결과(증기농도분포)는 수치해석 결과와 잘 일치하였다.

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수치모사를 통한 가스-스팀 발사체계의 열유동과 탄의 운동성능 예측 (A Numerical Prediction for the Thermo-fluid Dynamic and Missile-motion Performance of Gas-Steam Launch System)

  • 김현묵;배성훈;배대석;박철현;전혁수;김정수
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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    • pp.591-595
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    • 2017
  • 이상유동 모델과 동적격자계를 활용하여 탄의 사출관 내부의 열유동과 탄의 운동성능을 해석하는 수치모사를 진행하였다. 고온의 공기와 냉각제간의 상호작용 및 유동장을 해석하기 위해, Realizable $k-{\varepsilon}$ 난류 모델과 VOF (Volume Of Fluid) 모델을 선정하고 냉각제 유량변이에 따른 수치 해석을 진행하였다. 해석결과, 사출관의 압력은 냉각제의 유뮤에 따라 큰 차이를 보였고, 냉각제량에 따라서도 각각의 차이를 보였다. 탄의 속도와 가속도의 변이는 압력에 종속하여 나타났다.

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격자크기에 따른 Gun식 가스버너의 스월유동에 대한 난류모델평가 (Evaluation of Turbulent Models on the Swirling Flow of a Gun-Type Gas Burner According to the Mesh Size)

  • 김장권;오석형
    • 동력기계공학회지
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    • 제18권3호
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    • pp.59-65
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    • 2014
  • The computational fluid dynamics was carried out to evaluate turbulent models on the swirling flow of a gun-type gas burner(GTGB) according to the mesh size. The commercial SC/Tetra software was used for a steady-state, incompressible and three-dimensional numerical analysis. In consequence, the velocity magnitude from the exit of a GTGB and the flowrate predicted by the turbulent models of MP k-${\varepsilon}$, Realizable k-${\varepsilon}$ and RNG k-${\varepsilon}$ agree with the results measured by an experiment very well. Moreover, the turbulent kinetic energy predicted by the turbulent model of standard k-${\varepsilon}$ with mesh type C only agrees with the experimental result very well along the radial distance. On the other hand, the detailed prediction of the information of swirling flow field near the exit of a GTGB at least needs a CFD analysis using a fairly large-sized mesh such as a mesh type C.

$45^{\circ}$ 원형충돌분류의 난류혼합유동장에 대한 수치해석 (Numerical Analysis on the Turbulent Mixing Flow Field of $45^{\circ}$ Impinging Round Jet)

  • 김장권;오석형
    • 동력기계공학회지
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    • 제15권3호
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    • pp.38-45
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    • 2011
  • The computational flow numerical analysis was introduced to predict thc turbulent characteristics in the mixing flow structure of $45^{\circ}$ impinging round jet. This analysis has been carried out through the commercial fluent software. Realizable(RLZ) k-${\varepsilon}$ was used as a turbulent model. It can be known that mean velocities analysed through RLZ k-${\varepsilon}$ turbulent model comparatively predict well the experiments and show well the elliptic shape of mixing flow structure in the Y-Z plane, but analysed turbulent kinetic energies show somewhat differently from the experiments in certain regions.