• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.4
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• pp.357-368
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• 1993

With the assumption of the diffusion dominated flow, a numerical model has been developed for undertow and turbulence structure under the breaking wave by using the $textsc{k}$-$\varepsilon$ turbulence model. Undertow is a strong mean current which moves seqwards below the level of wave trough in the surf zone. The turbulence, generated by wave breaking in the roller, spreads and dissipates downwards. The governing equations are composed of the equation of motion with the period-averaged shear stress due to waves; $textsc{k}$- and $\varepsilon$-equations with the turbulence energy Production due to wave breaking. They are discretised by the three-level fully implicit scheme, which can be solved by using Thomas algorithm. The model gives good agreements with measurements except for the station that is closest to the breaking point.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.9
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• pp.1183-1192
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• 2001

The numerical simulation has been conducted for the investigation of flow and heat transfer characteristics of an oblique impingement jet injected to a flat plate. The finite volume method was used to discretize the governing equations based on the non-orthogonal coordinate with non-staggered variable arrangement. The $textsc{k}$-$\varepsilon$-ν(sup)'2 turbulence model was employed to consider the consider the anisotropic flow characteristics generated by the impingement jet flow. The predicted results were compared with the experimental data and those of the standard $textsc{k}$-$\varepsilon$ turbulence model. The results of the $textsc{k}$-$\varepsilon$-ν(sup)'2 model showed better agreement with the experimental data than those of the standard $textsc{k}$-$\varepsilon$ model. In order to get the optimum condition, the flow and temperature fields were calculated with a variation of inclined angle($\alpha$=30$^{\circ}$~90$^{\circ}$) and the distance between the jet exit and impingement plate-to-diameter (L/D=4~10) at a fixed Reynolds number(Re=20,000). For a small L/D, the near-peak Nusselt numbers were not significantly effected by the inclined angle. The near-peak Nusselt numbers were not significantly affected by the L/D in the case of a large $\alpha$. The overall shape of the local Nusselt numbers was influenced by both the jet orifice-to-plate spacing and the jet angle.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.6
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• pp.123-134
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• 1999

Nowadays since the automobile is regarded as the third living space, comfortable conditions are required in the passenger compartment. The customer's concern on air-conditioning/heating, ventilation and demisting/defrosting performances has been much increased. Both ventilation and demisting /defrosting performances are directly influenced by register location, shape of regist guide vane, ventilation flow rate, air distribution , and air circulation pattern. Diffuse plume of air from the register is desirable not only to maintain comfort when the comfort when the comfortable condition has been satisfied but to improve demisting /defrosting performance. In this study, experimental and numerical investigation about the flow field of six different register vane types were carried out , respectively. The numerical analysis, based upon the $textsc{k}$-$\varepsilon$ turbulence model , was applied to the air flow field. The results show that the shape of register guide vane should be considered as an important design paramter.

• 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.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.3
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• pp.205-215
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• 1994

A 3-dimensional numerical model of wind-induced flows has been established. and comparative evaluation of determination methods of vertical eddy viscosity has been performed. The model uses turbulence models to calculate vertical eddy viscosity. The examined methods arp 0-equation model of functional form, 1-equation model of turbulence kinetic energy, and two 2-equation models ($textsc{k}$-$\varepsilon$ and $textsc{k}$-ι models). The evaluation includes the verification tests against experimental data for wind-driven current On a closed one-dimensional channel and a recirculating one-dimensional channel. Comparative study of turbulence models has shown that the proper distribution of turbulence scale is parabolic and the eddy viscosity is depending strongly on mixing depth due to wind.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.73-81
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• 1997

Numerical analysis on turbulent flow and heat transfer in the rocket nozzle has been studied using the mass-weighted-averaged full Navier-Stokes equations, the Morkovin hypothesis on turbulent flow, the $\textsc{k}$-$\varepsilon$ turbulence model with the wall function specially designed to be able to consider the effects of pressure gradients, heat transfer and compressibility, and the numerical scheme of Karki. The present results are in good agreement with the experiments of Back et al.

• Journal of Environmental Science International
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• v.2 no.1
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• pp.17-26
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• 1993

The layer that is directly influenced by ground surface is called the atmospheric boutsdary layer in comparison with the free atmosphere of higher layer. In the boundary layer, the changes of wind, temperature and coefficient of turbulent diffusion in altitude are large and have great influences an atmospheric diffusion. The purpose of this paper is to express the structure and characteristics of development of mixed layer by using laboratory experiment and numerical simulation. Laboratory experiment using water tank are performed that closely simulate the process of break up of nocturnal surface inversion above heated surface and its phenomena are analyzed by the use of horizontally averaged temperature which is observed. The result obtained from the laboratory experiment is compared with theoretical ones from ; \textsc{k}-\varepsilon numerical model. The results are summarized as follows. 1) The horizontally averaged temperature was found to vary smoothly with height and the mixed layer developed obviously being affected by the convection. 2) The mean height of mixed layer may be predicted as a function of time, knowing the mean initial temperature gradient. The experimental values are associated well with the theoretical values computed for value of the universal constant $C_r$= 0.16, our $C_r$ value is little smaller than the value found by Townsend and Deardoru et al.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.170-177
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• 1989

The non-linear k-.epsilon. model developed by Speziale was employed for the prediction of developing turbulent flow in a square duct. The numerical procedure incorporated a finite volume method using a strong conservation form of the partially-parabolized Navier-Stokes equation. Results of the calculation were compared with available experimental data on the mean velocity field and turbulent kinetic energy, and was found to be in favorable agreement.

• Journal of Korea Water Resources Association
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• v.37 no.6
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• pp.461-466
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• 2004

This study presents a combined experimental and numerical effort to investigate wave breaking of sinusoidal waves in a surf zone. Numerical predictions are verified by comparing to laboratory measurements. The model solves the Reynolds equations and$textsc{k}$-$\varepsilon$ models for the turbulence analysis. To track the free surface displacement, the volume of fluid method is employed. As the height of incident wave increases, the wave breaking occurs at a closer point of the slope in the numerical model and laboratory experiments with the same depth and period. When a wave breaking occurs, the ratio of wave height becomes larger, with the same wave height and depth, as the period increases.

• Journal of Korea Water Resources Association
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• v.30 no.3
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• pp.201-210
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• 1997

To analyze the flow through open-channel constrictions using $\kappa$-$\varepsilon$ turbulence mode, a numerical model is developed. The simulated results agree well with existing experimental data which attributes to the adequate input of turbulent eddy-viscosity by turbulence model. A stream function and velocity distributions enable the analysis of flow characteristics at the downstream of constriction. Turbulent eddy viscosities over channel are spatially varied with stream pattern. For the evaluation of rapidly varied flow, the eddy-viscosity input by turbulence model is required instead of the empirical effective viscosity to solve a shallow water equation.