• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.566-570
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• 2012

본 연구에서는 비선형 k-$\varepsilon$ 모형을 이용하여 직사각형 개수로에서 평균흐름과 난류구조를 모의하였다. 표준 k-$\varepsilon$ 난류모형은 난류의 등방성을 가정하여 국부적 평형상태에서 계산하기 때문에 유선에 따른 레이놀즈 응력의 변형이 큰 경우나 이방성이 강한 경우 이를 계산하지 못한다. 이를 보완하기 위하여 제시된 것이 비선형 k-$\varepsilon$ 난류모형이다. 본 연구에서는 표준 k-$\varepsilon$ 모형과 비선형 k-$\varepsilon$ 모형에 의한 모의결과를 비교하였다. 난류모형을 검증하기 위하여 직사각형 개수로에 흐름을 완전 발달된 등류로 가정하여 해석하였다. 지배방정식을 해석하기 위해 Patankar와 Spalding (1972)이 제시한 SIMPLER 알고리즘을 사용하였고 유한체적법을 이용하여 이산화하고 엇갈린 격자체계를 사용하여 계산에서 발생하는 과도한 진동을 줄였다. 또한 차분기법은 Patankar (1980)가 제시한 Power-law 기법을 채택하였으며 경계조건으로 2층 벽법칙 모형과 Hossain과 Rodi (1993)의 모형을 이용하였다. 두 모형의 적용성을 검증하기 위하여 실측자료를 이용하여 비교하였고 그 결과 비선형 k-$\varepsilon$ 모형이 표준 k-$\varepsilon$ 모형에 비해 좀 더 실측지에 가깝게 모의하는 것을 볼 수 있었다.

• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.281-290
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• 2015

Numerical simulations of free surface flow over a broad-crested rectangular weir are conducted by using the volume of fraction (VOF) method and three different turbulence models, the k-${\varepsilon}$, RNG k-${\omega}$ and k-${\omega}$ SST models. The governing equations are solved by a second-order accurate finite volume method and the grid sensitivity study of solutions is carried out. The numerical results are evaluated by comparing the solutions with experimental and numerical results of Kirkgoz et al. (2008) and some non-dimensionalized experimental results obtained by Moss (1972) and Zachoval et al. (2012). The results show that the present numerical model can reasonably reproduce the experimental results, while three turbulent models yield different numerical predictions of two distinct zones of flow separation, the first zone is in front of the upstream edge of the weir and the second is created immediately behind the upstream edge of the weir where the flow is separated to form the separation bubble. The standard k-${\varepsilon}$ model appears to significantly underestimate the size of both separation zones and the k-${\omega}$ SST model slightly over-estimates the first separation zone in front of the weir. The RNG k-${\varepsilon}$ model predicts both separation zones in overall good agreement with the experimental measurement, while the k-${\omega}$ SST model yields the best numerical prediction of separation bubble at the upstream edge of the weir.

• Journal of Ocean Engineering and Technology
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• v.14 no.4
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• pp.9-16
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• 2000

This paper deals with the numerical and experimental study on the characteristics of the flow around a sunken vessel. Numerical simulation of the two dimensional steady flow on the midship section are carried out by the CFD code which is developed by using finite volume method and which includes the standard $textsc{k}$-$\varepsilon$ model with standard wall function. A experimental study is also carried out for the 1/100 scale model in circulating water channel. A velocity fields around the ship are measuremed by using particle image velocimetry technique. And the fluid forces acting on the ship hull by uniform current are measured by two axis load cell. The computed and measured velocity fields on the midship section are compared with each other in the view point of velocity dstribution and reattachement length, which shows good agreement in quality. The drag force on the vessel also showed the same tendency in both computational and experimental results. However, the quantitative disagreements are shown due to the three dimensional effect of the experiment. The result are used to determine the functional efficiency and stability of the vessel as a artificial reef.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1940-1954
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• 1992

Fine grid computations were attempted to analyze the turbulent flows in the near wall low Reynolds number region and the numerical analyses were incorporated by a finite-volume discretization with full find grid system and low Reynolds number k-.epsilon. model was employed in this region. For the improvement of low Reynolds number k-.epsilon. model, modification coefficient of eddy viscosity $f_{\mu}$ was derived as a function of turbulent Reynolds number $R_{+}$ and nondimensional length $y^{+}$ from the concept of two length scales of dissipation rate of turbulent kinetic energy. The modification coefficient $f_{\epsilon}$ in .epsilon. transport equation was also derived theoretically. In the turbulent kinetic energy equation, pressure diffusion term was added in order to consider low Reynolds number region effect. The main characteristics of this low Reynolds number k-.epsilon. model were founded as : (1) In high Reynolds number region, the present model has limiting behavior which approaches to the high Reynolds number model. (2) Present low Reynolds number k-.epsilon. model dose not need additional empirical constants for the transport equations of turbulent kinetic energy and dissipation of turbulent kinetic energy in order to consider wall effect. Present low Reynolds number turbulence model was tested in the pipe flow and obtained improved results in velocity profiles and Reynolds stress distributions compared with those from other k-.epsilon. models.s.s.

• 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.

• 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.