• Wind and Structures
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• v.9 no.5
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• pp.357-367
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• 2006

Unsteady 3D Reynolds Averaged Navier-Stokes (URANS) solver is used to simulate the turbulent flow past an isolated prismatic cylinder at Re=37,400. The aspect ratio of height to base width of the body is 5. The turbulence closure is achieved through a non-linear $k-{\varepsilon}$ model. The applicability of this model to predict unsteady forces associated with this flow is examined. The study shows that the present URANS solver with standard wall functions predicts all the major unsteady phenomena showing closer agreement with experiment. This investigation concludes that URANS simulations with the non-linear $k-{\varepsilon}$ model as a turbulence closure provides a promising alternative to LES with view to study flows having complex features.

• 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.

• Wind and Structures
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• v.5 no.1
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• pp.15-24
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• 2002

This paper reports the numerical calculations of uniform turbulent shear flow around a square cylinder. The predictions are obtained by solving the two-dimensional unsteady Navier-Stokes equations in a finite volume technique. The turbulent fluctuations are simulated by the standard $k-{\varepsilon}$ model and one of its variant which takes care of the realizability constraint in order to suppress the excessive generation of turbulence in a stagnation condition. It has been found that the Strouhal number and the mean drag coefficient are almost unaffected by the shear parameter but the mean lift coefficient is increased. The present predictions are compared with available experimental data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6B
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• pp.643-651
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• 2008

In the present paper, turbulent open-channel flows over longitudinal bedforms are numerically simulated. The Reynolds- averaged Navier-Stokes equations in curvilinear coordinates are solved with the non-linear $k-{\varepsilon}$ model by Speziale( 1987). First, the developed model is applied to rectangular open channel flows for purposes of model validation and parameter sensitivity studies. It is found that the parameters $C_D$ and $C_E$ are important to the intensity of secondary currents and the level of turbulent anisotropy, respectively. It is found that the non-linear $k-{\varepsilon}$ model can hardly reproduce the turbulence anisotropy near the free surface. However, the overall pattern of the secondary currents by the present model is seen to coincide with measured data. Then, numerical simulations of turbulent flows over longitudinal bedforms are performed, and the simulated results are compared with the experimental data in the literature. The simulated secondary currents clearly show upflows and downflows over the ridges and troughs, respectively. The numerical results of secondary currents, streamwise mean velocity, and turbulence structures compare favorably with the measured data. However, it is observed that the secondary currents towards the troughs were significantly weak compared with the measured data.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.4
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• pp.101-107
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• 1998

A three-dimensional multi-phase flow is simulated around a smooth tire. This simulation is conducted by solving Navier-Stokes equation with a k-$\varepsilon$ turbulent model. The numerical calculations are carried out by modeling a multi-phase free surface flow mixed with air and water at the inlet. The numerical solutions show an intuitively resonable behavior of water around a moving tire. The calculated pressure around the tire surface along the moving direction is presented. The moving velocities of the tire are chosen to be 30, 40, 60, and 70 km/h. The numerically simulated pressures around the tire are compared with existing experimental data. The comparison shows a new possible tool of analyzing a hydroplaning phenomenon for an automobile tire by means of a computational fluid dynamics.

• 한국연소학회:학술대회논문집
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• 1997.06a
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• pp.163-173
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• 1997

This article presents an application of a large-scale structural mixing model (Broadwell et al. 1984) to the blowout of turbulent reacting jets discharging perpendicularly into an unconfined cross air-flow. In an analysis of a common stability curve, a plausible explanation can be made that the phenomenon of blowout is related only to the mixing time scale of the two flows. The most notable observation is that the blowout distance is traced at fixed positions at all times according to the velocity ratio R. Measurements of the lower blowout limits in the liftable flame agree qualitatively with the blowout parameter ${\varepsilon}$, proposed by Broadwell et al. Good agreement between the results calculated by a modified blowout parameter ${\varepsilon}^'$ and experimental results confirms the important effect of a large-scale structure in specifying the stabilization feature of blowouts.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.06a
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• pp.35-38
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• 1998

The momentum, heat and mass transport in the melt of several sizes of crucibles are calculated using a three dimensional numerical simulation technique with and without the k-$\varepsilon$ turbulent model. When turbulent model is not used, non-axisymmetric profiles of velocity, temperature and oxygen concentration appear in the melt of all sizes of crucibles. Axisymmetric profiles are obtained when the k-$\varepsilon$ model is adopted.

• Fire Science and Engineering
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• v.17 no.3
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• pp.13-19
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• 2003

In this paper, numerical calculations are conducted to predict the characteristics of the heat transfer and smoke propagation in a cydodrome. The gas flow velocity and temperature around the origin of the fire is obtained by using a plume model and the turbulent flow characteristics are considered by standard $textsc{k}$-$\varepsilon$ turbulent model. In this study, the transient thermal behavior can be used for designing fire detection of large rooms.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.607-621
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• 1988

The paper describes the incorporation of an algebraic stress model(ASM) of turbulence in to a semi-elliptic solution procedure for the prediction of turbulent flow in passage around a 180.deg. square sectioned bend. The numerical results are obtained from a finite-volume discretization with applications of QUICK scheme and full find grid system without PSL approximation. Results show that the better agreements in velocity profiles with experimental data than those from k, $\varepsilon$ equation model with wall function and PSL are obtained. Predictions of Reynolds stresses also show good agreements with the experimental data.

• Journal of Korea Water Resources Association
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• v.50 no.9
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• pp.637-646
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• 2017

This study presents a numerical model for simulating dense interflows. The governing equations are provided and the finite difference method is used with the $k-{\varepsilon}$ turbulence model. The model is used to simulate a dense interflow established in a deep ambient water, resulting velocity and excess density profiles. It is observed that velocity decreases in the longitudinal direction due to water entrainment in the vicinity of the outlet and rarely changes for increased Richardson number. Similarity collapses of velocity and excess density are obtained, but those of turbulent kinetic energy and dissipation rate are not. A shape factor for the dense interflow is obtained from the simulated profiles. The value of this shape factor can be used in the layer-averaged modeling of dense interflows. In addition, a buoyancy-related parameter ($c_{3{\varepsilon}}$) for the $k-{\varepsilon}$ model and the volume expansion coefficient (${\beta}_0$) are obtained from the simulated results.