• Title/Summary/Keyword: k-$\varepsilon$ 난류모형

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Numerical Calculation of Viscous Flows for Two HSVA Tankers (HSVA 두 탱커 선형에 대한 점성유동 계산)

  • Kwak, Young-Ki
    • Journal of Ocean Engineering and Technology
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    • v.13 no.2 s.32
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    • pp.138-146
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    • 1999
  • The viscous flow around a ship hull is calculated by the use of RANS(Reynolds-averaged Navier-Stokes) solver. Reynolds stresses are midelled by using the k-${epsilon}$ turbulence model and the law is applied near the body. Body fitted corrdinates are introduced for the treatment of the complex boundary of the ship hull form and the governing equations in the physical domain transformed into ones in the computational domain. The transformed equations are numerically solved by an employment of FVM(Finite Volume Method). SIMPLE(Semi-Implicit Pressure Linked Equation) method is adopted in the calculation of pressure and the solution of the sidcretized equation is obtained by the line-by-line method with the use of TDMA(Tri-Diagonal Matrix Algorithme). To assure the proprietty of this computing method, HSVA tanker and Dyne hull are calculated ar both model and ship scale Reynolds number. Their reaults of pressure distributions on fore and aft body, axial velocity contours and transverse velocity velocity vectors and viscous resistance coefficients are compared with other's experiments and calculations.

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Numerical Simulation of Turbulent Separated and Reattaching Flows by Local Forcing (국소교란에 의한 난류박리 재부착 유동의 수치해석)

  • Rhee, Gwang-Hoon;Sung, Hyung-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.3
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    • pp.467-476
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    • 2000
  • An unsteady numerical simulation was performed for locally-forced separated and reattaching flow over a backward-facing step. The local forcing was given to the separated and reattaching flow by means of a sinusoidally oscillating jet from a separation line. A version of the $k-{\varepsilon}-f_{\mu}$ model was employed, in which the near-wall behavior without reference to distance and the nonequilibrium effect in the recirculation region were incorporated. The Reynolds number based on the step height (H) was fixed at $Re_H=33000$, and the forcing frequency was varied in the range $0{\leq}St_H{\leq}2$. The predicted results were compared and validated with the experimental data of Chun and Sung. It was shown that the unsteady locally-forced separated and reattaching flows are predicted reasonably well with the $k-{\varepsilon}-f_{\mu}$ model. To characterize the large-scale vortex evolution due to the local forcing, numerical flow visualizations were carried out.

Experimental and Numerical Studies of the Flowfield around an Axisymmetric Body (축대칭 물체 주위유동의 실험적·수치적 연구)

  • Ahn, Jong-Woo;Song, In-Haeng;Park, Tae-Sun
    • Journal of the Society of Naval Architects of Korea
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    • v.34 no.3
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    • pp.9-18
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    • 1997
  • Experimental and numerical studies are carried out to investigate flow characteristics around an axisymmetric body with and without a compound propulsor. The effects of a compound propulsor are investigated as measuring the surface pressure distribution and the velocity profiles using LDV system in the cavitation tunnel of KRISO. The incompressible Reynolds-Averaged Navier-Stokes(RANS) equations are also solved using the finite volume method. The standard k-${\varepsilon}$ turbulence model is adopted for turbulence closure. In order to calculate propeller-hull interaction, the induced velocity calculated by lifting surface theory is considered as the boundary condition at the propeller plane. The experimental data obtained in this study can provide a useful database for development and validation of CFD code.

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Numerical Study of the Flow Field Around an Axisymmetric Body with Integrated Propulsors (복합추진장치가 포함된 축대칭 물체 주위유동의 수치적 연구)

  • Jong-Woo Ahn;Il-Sung Moon;Sang-Woo Pyo;Jung-Chun Suh
    • Journal of the Society of Naval Architects of Korea
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    • v.36 no.4
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    • pp.1-8
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    • 1999
  • Numerical study is carried out to investigate flow characteristics around an axisymmetric body with and without an integrated propulsor. The incompressible Reynolds-Averaged Navier-Stokes(RANS) equations are also solved using the finite volume method and the standard $k-\varepsilon$ turbulence model for turbulence closure. In order to investigate the propulsor-hull interaction, the induced velocity calculated by surface panel methods is utilized for the boundary condition at the propeller plane. The calculated results are compared to the experimental results. It is considered that the present numerical code can be used for design of an integrated propulsor.

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Study on the Scale Effect of Viscous Flows around the Ship Stern (선미 점성 유동장에 미치는 척고효과에 관한 연구)

  • Kwak, Y.K.;Min, K.S.;Oh, K.J.;Kang, S.H.
    • Journal of the Society of Naval Architects of Korea
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    • v.34 no.1
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    • pp.1-10
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    • 1997
  • Viscous flow around actual ship is calculated by an use of RANS equations. The propriety of this computing method, usefulness to hull form design and the scale effect which is the effect of viscous flow depending on the scale of ship model are investigated. Reynolds stress is modelled by using k-${\varepsilon}$ turbulence model and the law of wall is applied near the body. Body fitted coordinates are introduced for the treatment of the arbitrary 3-dimensional shape of the ship hull form. The transformed equations in the computational domain are numerically solved by an employment of FVM. In the calculation of pressure, SIMPLE method is adopted and the solution of the discretized equation is obtained by the line-by-line method with the use of TDMA The calculations of two ships, 4410 TEU container carrier and 50,000 DWT class bulk carrier, are performed at model and actual ship scale. The results are compared and discussed with the model test results which are viscous resistance, nominal wake distribution at propeller plane and limiting streamline on the hull surface. They describe the effect of stem form and the scale effect very well. In particular, the calculated nominal wake distribution and limiting streamline are agreed qualitatively with the experiments and the viscous resistance values are estimated within ${\pm}5%$ difference from the resistance tests.

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

  • Oh, Jeong-Seog;Lee, Won-Nam;Lee, Jong-Geun;Santavicca, Dominique A.
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2010.11a
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    • pp.386-392
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    • 2010
  • The multiphase simulation of a liquid jet in a lab-scale ramjet combustor with a plain orifice type injector was studied with a commercial CFD tool, a FLUENT program. The objectives of the current study are to analysis the breakup characteristics of a hexane liquid jet in a cross flow and to derive the correlation between flow conditions and drag force coefficients in a test section. From the result of a numerical simulation, we concluded that a DPM and Realizable $k-{\varepsilon}$ model with an enhanced wall treatment were available to simulate the multiphase flow simulation. And the calculated distribution of a hexane vapor concentration was well-matched with experimental results.

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Numerical Simulation of Turbulent Flow in n Wavy-Walled Channel (파형벽면이 있는 채널 내의 난류유동에 대한 수치해석)

  • Park, Tae-Seon;Sung, Hyung-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.5
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    • pp.655-667
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    • 2003
  • Turbulent flow over a fully-developed wavy channel is investigated by the nonlinear $k-\varepsilon-f_\mu$ model of Park et al.(1) The Reynolds number is fixed at $Re_{b}$ = 6760 through all wave amplitudes and the wave configuration is varied in the range of $0\leq\alpha/\lambda\leq0.15$ and $0.25\leq{\lambda}/H\leq4.0$. The predicted results for wavy channel are validated by comparing with the DNS data of Maa$\beta$ and Schumann(2) The model performance Is shown to be generally satisfactory. As the wave amplitude increases, it is found that the form drag grows linearly and the friction drag is overwhelmed by the form drag. In order to verify these characteristics, a large eddy simulation is performed for four cases. The dynamic model of Germane et al.(3) is adopted. Finally, the effects of wavy amplitude on separated shear layer are scrutinized.

Numerical Analysis of Tip Vortex and Cavitation of Elliptic Hydrofoil with NACA 662-415 Cross Section (NACA 662-415 단면을 가지는 타원형 수중익의 날개 끝 보오텍스 및 캐비테이션 수치해석)

  • Park, Il-Ryong;Kim, Je-in;Seol, Han-Sin;Kim, Ki-Sup;Ahn, Jong-Woo
    • Journal of Ocean Engineering and Technology
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    • v.32 no.4
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    • pp.244-252
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    • 2018
  • This paper provides quantification of the effects of the turbulence model and grid refinement on the analysis of tip vortex flows by using the RANS(Reynolds averaged Navier-Stokes) method. Numerical simulations of the tip vortex flows of the NACA $66_2$-415 elliptic hydrofoil were conducted, and two turbulence models for RANS closure were tested, i.e., the Realizable $k-{\varepsilon}$ model and the Reynolds stress transport model. Numerical results were compared with available experimental data, and it was shown that the data for the Reynolds stress transport model that were computed on the finest grid system had better agreement in reproducing the development and propagation of the tip vortex. The Realizable $k-{\varepsilon}$ model overestimated the turbulence level in the vortex core and showed a diffusive behavior of the tip vortex. The tip vortex cavitation on the hydrofoil and its trajectory also showed good agreement between the current numerical results that were obtained using the Reynolds stress transport model and the results observed in the experiment.

Numerical Simulation of Turbulent Heat Transfer in Locally-Forced Separated and Reattaching Flow (국소교란에 의한 박리 재부착 유동에서의 난류 열전달 수치해석)

  • Ri, Gwang-Hun;Seong, Hyeong-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.1
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    • pp.87-95
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    • 2001
  • A numerical study was made of heat transfer in locally-forced turbulent separated and reattaching flow over a backward-facing step. The local forcing was given to the flow by means of sinusoidally oscillating jet from a separation line. A Rhee and Sung version of the unsteady $\kappa$-$\varepsilon$-f(sub)u model and the diffusivity tensor heat transfer model were employed. The Reynolds number was fixed at Re(sub)H=33,000 and the forcing frequency was varied in the range 0$\leq$fH/U(sub)$\infty$$\leq$2. The condition of constant heat flux was imposed at the bottom wall. The predicted results were compared and validated with the experimental data of Chun and Sung and Vogel and Eaton. The enhancement of heat transfer in turbulent separated and reattaching flow by local forcing was evaluated and analyzed.

A Necessity at Introducing the Volume Ratio in the Computation Vegetated Flow (식생흐름 계산에서 체적비 도입의 필요성)

  • Kim, Mujong;Lee, Seonmin;Choi, Sung-Uk
    • Proceedings of the Korea Water Resources Association Conference
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    • 2015.05a
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    • pp.177-177
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    • 2015
  • 개수로에서 식생은 항력을 발생하여 평균유속을 감소시킬 뿐만 아니라, 식생영역과 비식생영역의 경계에서 유속 차를 발생시켜 일반 개수로 흐름보다 복잡한 흐름구조를 형성한다. 또한, 식생은 개수로 흐름에서 부피를 차지하여 식생영역의 유량을 감소시킨다. 일반적으로 식생이 식재된 개수로 흐름을 수치모의 할 경우 체적비를 고려하지 않을 때가 많다. 하지만 물과 식생의 체적비가 높을 경우, 식생에 의한 부피를 고려하지 않으면 실제 유속을 과다산정 하여 흐름모의가 정확하지 않다. 그러므로 식생이 있는 흐름을 정확히 수치모의하기 위해 식생의 체적비를 고려하여 실제 유속을 산정하는 것은 매우 중요하다. 본 연구에서는 식생된 개수로 흐름의 수치모의에서 체적비 도입의 필요성을 분석하였다. $k-{\varepsilon}$ 난류모형을 이용하여 수치모의를 수행하였고, 지배방정식에 식생항을 추가하여 식생이 식재된 개수로 흐름을 모의하였다. 식생 체적비를 고려하기 위해 지배방정식에 식생 체적비에 관한 항을 추가하였다. 체적비 도입의 필요성을 알아보기 위해 선행연구의 침수식생 실험수로를 대상으로 수치모의하였다. 식생밀도가 낮은 경우 식생 체적비의 고려 유 무가 모의결과에 미치는 영향이 작았으나, 식생밀도가 높은 경우에는 식생 체적비를 고려한 경우가 보다 정확한 모의결과를 도출 할 수 있었다.

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