• Journal of Advanced Marine Engineering and Technology
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• v.38 no.6
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• pp.615-624
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• 2014

The fin-tube heat exchanger being used for industrial boiler, radiator, refrigerator has been conducted in various studies to improve it's performance. In this study, the characteristics of heat transfer and pressure drop was theoretically analyzed according to longitudinal pitch, location of vortex generator, bump phase and number of the tube surface about the plain fin-tube heat exchanger. The boundary condition for the CFD (Computational Fluid Dynamics) analysis applied with the SST (Shear Stress Transport) turbulence model assumed as the tube surface temperature of 333 K, the inlet air temperature of 423-438 K and the inlet air velocity of 1.5~2.1 m/s. The analysis results indicated that the heat transfer coefficient is not affected highly by the longitudinal pitch, and the heat transfer characteristics was more favorable when the vortex generator was located in front of the tube. Also the bump phase of the tube surface indicated that circle type was more appropriate than serrated type and triangle type in the characteristics of heat transfer and pressure drop, and the sixteen's bump phase of circle type was most favorable.

• Journal of the Korean Society of Visualization
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• v.20 no.3
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• pp.102-108
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• 2022

In the fan module of the intercooling refrigerator, a drain hole structure was designed for stable drainage of defrost water. However, the airflow passing through the drain hole can disturb flow features around the evaporator. Since this backflow leads to an increase in flow loss, the accurate experimental and numerical analyses are important to understand the flow characteristics around the fan module. Considering the complex geometry around the fan module, three different turbulence models (Standard k-ε model, SST k-ω model, Reynolds stress model) were used in computational fluid dynamics (CFD) analysis. According to the quantitative and qualitative comparison results, the Standard k-ε model was most suitable for the research object. High-accuracy results well match with the experiment result and overcome the limitation of the experiment setup. The method used in this study can be applied to a similar research object with an orifice outflow driven by a rotating blade.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.240-243
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• 2005

This study deals with the shape optimization of a wire spacer fuel assembly of Liquid Metal Reactors (LMRs). The Response Surface based optimization Method is used as an optimization technique with the Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer using Shear Stress Transport (SST) turbulence model as a turbulence closure. Two design variables namely, pitch to fuel rod diameter ratio and lead length to fuel rod diameter ratio are selected. The objective function is defined as a combination of the heat transfer rate and the inverse of friction loss with a weighting factor. Three level full-factorial method is used to determine the training points. In total, nine experiments have been performed numerically and the resulting datas have been analysed for optimization study. Also, a comparison has been made between the optimized surface and the reference one in this study.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.185-190
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• 2005

This work presents a numerical procedure to optimize the elliptic-shaped pin fin arrays to enhance turbulent heat transfer. The response surface method is used as an optimization technique with Reynolds-averaged Navier Stokes analysis of flow and heat transfer. Shear stress transport (SST) turbulence model is used as a turbulence closure. Computational results for average heat transfer rate show a reasonable agreement with the experimental data. Four variables including major axis length, minor axis length, pitch and the pin fin length nondimensionalized by duct height are chosen as design variables. The objective function is defined as a linear combination of heat transfer and friction-loss related terms with weighting factor. D-optimal design is used to reduce the data points, and, with only 28 points, reliable response surface is obtained. Optimum shapes of the pin-fin arrays have been obtained in the range from 0.0 to 0.1 of weighting factor.

• Nuclear Engineering and Technology
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• v.53 no.10
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• pp.3207-3216
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• 2021

Three-dimensional structures of a vortical flow field and heat transfer characteristics in a partially blocked 7-pin fuel assembly mock-up of sodium-cooled fast reactor have been investigated through a numerical analysis using a commercial computational fluid dynamics code, ANSYS CFX. The simulation with the SST turbulence model agrees well with the experimental data of outlet and cladding wall temperatures. From the analysis on the limiting streamline at the wall, multi-scale vortexes developed in axial direction were found around the blockage. The vortex core has a high cladding wall temperature, and the attachment line has a low cladding wall temperature. The small-scale vortex structures significantly enhance the convective heat transfer because it increases the turbulent mixing and the turbulence kinetic energy. The large-scale vortex structures supply thermal energy near the heated cladding wall surface. It is expected that control of the vortex structures in the fuel assembly plays a significant role in the convective heat transfer enhancement. Furthermore, the blockage plate and grid spacer increase the pressure drop to about 36% compared to the bare case.

• Journal of the Korean Society of Visualization
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• v.21 no.2
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• pp.55-62
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• 2023

The characteristic of jet impinging on the concave surface were analyzed through thermographic phosphor thermometry (TPT) and numerical investigation. Under a jet Reynolds number of 6600, nozzle diameters and nozzle-to-surface distances (H/d) were changed 5mm and 10mm and H/d=2 and 5. The RNG k-ε turbulence model can accurately predict the distribution of Nusselt number, compared to other models (SST k-ω, realizable k-ε). Heat transfer characteristics varied with the nozzle diameter and H/d, with a secondary peak noted at H/d =2, due to vortex-induced flow detachment and reattachment. An increase in nozzle diameter enhanced jet momentum, turbulence strength, and heat transfer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.53-60
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• 2002

Based on the analyses of the single transverse injection in supersonic flow fields, the mixing characteristics of dual transverse injection of hydrogen in supersonic air flow are studied with computational methods. Three-dimensional Navier -Stokes and the k-$\omega$ SST turbulence model were used. A parametric study is conducted with the variation of the distance between two injectors. The flow patterns and the mixing characteristics of two injection flows are very different from each other, and the flow patterns and the mixing characteristics of the rear injection flow are strongly influenced by those of the first injection flow. The increase of the distance between two injectors up to a specific distance results in the increase of mixing rate and penetration of fuel. However, the increase of the distance over the specific distance results in the decrease of mixing rate and penetration of fuel. From the results it can be stated that there exists a distance between two injectors for optimum mixing characteristics.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.3
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• pp.187-194
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• 2015

Course correction munition is a smart projectile which improves its accuracy by the control mechanism equipped in the fuze section with canard. In this paper, various aerodynamic configurations of the fuze section were analysed by utilizing a semi-empirical method and a CFD method. A final canard configuration showing the least drag was then determined. During the CFD simulation, it was found that the k-${\omega}$ SST turbulence model combined with O-type grid base is suitable for the prediction of the base drag. Finally, the aerodynamic characteristics of the smart munition and the change of drag due to the canard installation were analysed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.6
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• pp.475-484
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• 2012

Numerical investigation is performed to understand the effects of thickness uncertainty of a supporting airfoil due to manufacturing processes on the aerodynamic characteristics of an airfoil used for measuring data in a wind tunnel testing. This is done by comparing the coefficients of lift, drag and moment of the airfoils. In this work, the airfoil model consists of three parts, one located in the center for measuring and two outer parts used for supporting. The study is carried out with a NACA64-418 airfoil and the turbulence model of Transition SST. It is found that the effect of thickness uncertainty of the airfoils used for supporting is not significant to the performance of the test airfoil at various angles of attack and Reynolds numbers.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.147-162
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• 2021

The problem of predicting a ship's form factor and associated scale effects has been subject to many investigations in recent years. In this study, an attempt is made to investigate whether the form factor is influenced by a change in the ship's speed by numerically modelling a geosim series of the KCS hull form by means of a RANS solver. The turbulence dependence of the problem is also studied by altering the closure model among three widely used approaches (the k-𝜔, k-𝜔 SST, and k-𝜀 models). The results show that at very low speeds (Froude numbers in the range of 0.02-0.06) the numerical model predicts changes in the form factor of a ship between 10% and 20%, depending on the turbulence model and scale factor choices. As the speed is increased further, the form factor exhibits little change, usually in the range of 1% or less. Simulations where the Reynolds number is changed by approximately two orders of magnitude, achieved by altering the value of viscosity, confirmed that the form factor can be considered Froude-dependent only for low speeds, predicting essentially identical values when high speed cases are considered.