• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.1
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• pp.51-59
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• 2004

The effectiveness of one dimensional critical velocity method for evacuation environment at 10MW fire size in a railroad tunnel have been investigated in this paper by three dimensional CFD method. It was performed to evaluate the evacuation environment in terms of temperature distribution, visible distance distribution and CO concentration at some tunnel inlet velocity, 1m/s, 2m/s (near critical velocity), and 3m/s. At all inlet velocity, passenger should give away downward the flow direction because the inlet velocity can not afford to sufficient evacuation environment for passengers. In case of 3m/s inlet velocity, however, the evacuation environment for passengers is better than the other cases. To provide more safe evacuation environment on fire situation, tunnel inlet velocity should be larger than critical velocity.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.530-533
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• 2010

This paper presents numerical analysis and design optimization of various turbine blade cooling techniques with three-dimensional Reynolds-averaged Navier-Stokes(RANS) analysis. The fluid flow and heat transfer have been performed using ANSYS-CFX 11.0. A fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness with the radial basis neural network method. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. The impingement jet cooling has been performed to investigate heat transfer characteristic with geometry variables. Distance between jet nozzle exit and impingement plate, inclination of nozzle and aspect ratio of nozzle hole are considered as geometry variables. The area averaged Nusselt number is evaluated each geometry variables. A rotating rectangular channel with staggered array pin-fins has been investigated to increase heat transfer performance ad to decrease friction loss using KRG modeling. Two non-dimensional variables, the ratio of the eight diameter of the pin-fins and ratio of the spacing between the pin-fins to diameter of the pin-fins selected as design variables. A rotating rectangular channel with staggered dimples on opposite walls are formulated numerically to enhance heat transfer performance. The ratio of the dimple depth and dimple diameter are selected as geometry variables.

• Wind and Structures
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• v.17 no.6
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• pp.647-670
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• 2013

The paper presents a numerical approach to study of fluid flow characteristics and to predict performance of wind turbines. The numerical model is based on Finite-volume method (FVM) discretization of unsteady Reynolds-averaged Navier-Stokes (URANS) equations. The movement of turbine blades is modeled using moving mesh technique. The turbulence is modeled using commonly used turbulence models: Renormalization Group (RNG) k-${\varepsilon}$ turbulence model and the standard k-${\varepsilon}$ and k-${\omega}$ turbulence models. The model is validated with the experimental data over a large range of tip-speed to wind ratio (TSR) and blade pitch angles. In order to demonstrate the use of numerical method as a tool for designing wind turbines, two dimensional (2-D) and three-dimensional (3-D) simulations are carried out to study the flow through a small scale Darrieus type H-rotor Vertical Axis Wind Turbine (VAWT). The flows predictions are used to determine the performance of the turbine. The turbine consists of 3-symmetrical NACA0022 blades. A number of simulations are performed for a range of approaching angles and wind speeds. This numerical study highlights the concerns with the self-starting capabilities of the present VAWT turbine. However results also indicate that self-starting capabilities of the turbine can be increased when the mounted angle of attack of the blades is increased. The 2-D simulations using the presented model can successfully be used at preliminary stage of turbine design to compare performance of the turbine for different design and operating parameters, whereas 3-D studies are preferred for the final design.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.5
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• pp.367-375
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• 2017

RANS computational analysis was performed on the head of the launch vehicle including the hammerhead nose pairing in the supersonic regime. The two-dimensional axisymmetric analysis was performed by using laminar, fully turbulent and transition models and compared with the experimental data. It was observed that different flow phenomena occurred depending on the Reynolds number. Under the high Reynolds number condition, the boundary layer becomes turbulent, which is not separated from the surface of the launch vehicle. With the low Reynolds number condition, laminar separation bubble was produced due to the separation and reattachment of the boundary layer on the expansion-compression edge of the hammerhead type nose fairing. The three-dimensional computations with the angle of attack showed a fully detached vortical structure due to the laminar separation bubble. It is proved that the turbulent transition should be considered to predict the separation bubble with the Reynolds number.

• Wind and Structures
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• v.38 no.2
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• pp.129-146
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• 2024

Aiming at the problem of non-stationary wind field simulation of downbursts, a non-stationary down-burst generation system was designed by adding a nozzle and program control valve to the inlet of the original wall jet model. The computational fluid dynamics (CFD) method was used to simulate the downburst. Firstly, the two-dimensional (2D) model was used to study the outflow situation, and the database of working conditions was formed. Then the combined superposition of working conditions was carried out to simulate the full-scale measured downburst. The three-dimensional (3D) large eddy simulation (LES) was used for further verification based on this superposition condition. Finally, the wind tunnel test is used to further verify. The results show that after the valve is opened, the wind ve-locity at low altitude increases rapidly, then stays stable, and the wind velocity at each point fluctuates. The velocity of the 2D model matches the wind velocity trend of the measured downburst well. The 3D model matches the measured downburst flow in terms of wind velocity and pulsation characteris-tics. The time-varying mean wind velocity of the wind tunnel test is in better agreement with the meas-ured time-varying mean wind velocity of the downburst. The power spectrum of fluctuating wind ve-locity at different vertical heights for the test condition also agrees well with the von Karman spectrum, and conforms to the "-5/3" law. The vertical profile of the maximum time-varying average wind veloci-ty obtained from the test shows the basic characteristics of the typical wind profile of the downburst. The effectiveness of the downburst generation system is verified.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.3
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• pp.127-138
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• 2016

Diesel vehicles should be equipped with urea-selective catalytic reduction(SCR) system as a high-performance catalyst, in order to reduce harmful nitrogen oxide emissions. In this study, a three-dimensional Eulerian-Lagrangian CFD analysis was used to numerically predict the multiphase flow characteristics of the urea-SCR system, coupled with the chemical reactions of the system's transport phenomena. Then, the numerical spray structure was modified by comparing the results with the measured values from spray visualization, such as the injection velocity, penentration length, spray radius, and sauter mean diameter. In addition, the analysis results were verified by comparison with the removal efficiency of the nitrogen oxide emissions during engine and chassis tests, resulting in accuracy of the relative error of less than 5%. Finally, a verified CFD analysis was used to calculate the interanl flow of the urea-SCR system, thereby analyzing the characteristics of pressure drop and velocity increase, and predicting the uniformity index and overdistribution positions of ammonia.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.8
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• pp.781-787
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• 2011

We design a four-stage propane-refrigerant centrifugal compressor for an LNG plant. Using a commercial code, we aerodynamically designed the compressor at each design point of the corresponding stages. We estimated the one-dimensional aerodynamic design output and the three-dimensional shape of the impeller flow passage via three-dimensional flow analysis. In particular, we discuss in detail the flow characteristics of the impeller and the vaneless diffuser passages of the fourth-stage compressor in terms of the velocity fields, the pressure, and the entropy distributions of the flow passages. We include the flow effects of the tip clearance flow, because at this stage the rotating speed and total inlet pressure are higher than those at the other compressor stages are. We carried out performance tests of the designed compressor stages using propane as a refrigerant in the LNG cycle. The practical evaluation could lead to design enhancements in the future.

• Journal of computational fluids engineering
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• v.21 no.2
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• pp.54-61
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• 2016

When spent fuel assemblies from the reactor of nuclear power plants(NPPs) are transported, the assemblies are exposed to short-term operations that can affect the peak cladding temperature of spent fuel assemblies. Therefore, it needs to perform the analysis of heat transfer on spent fuel dry cask during the operation. For 3 dimensional computational fluid dynamnics(CFD) simulation, it is proposed that the short-term operation is divided into three processes: Wet, dry, and vacuum drying condition. The three processes have different heat transfer mode and medium. Metal transportation cask, which is Korea Radioactive Waste Agency(KORAD)'s developing cask, is evaluated by the methods proposed in this work. During working hours, the boiling at wet process does not occur in the cask and the peak cladding temperatures of all processes remain below $400^{\circ}C$. The maximum peak cladding temperature is $173.8^{\circ}C$ at vacuum drying process and the temperature rise of dry, and vacuum drying process occurs steeply.

• Journal of the Korean Society for Marine Environment & Energy
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• v.13 no.4
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• pp.263-269
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• 2010

The present study deals with the investigation about the improvement of performance of tidal stream turbine blade (HAT) with tip rake. HAT impeller has sometimes experienced noise and vibration by Tip vortex which causes even erosion and severe efficiency loss to the blade, The newly proposed tip rake impeller can make the tip vortex week compared with a normal impeller by preventing the three dimensional effect at tip region. In order to find out the optimum rake impeller, three cases have been designed and the performance of the designed rake impellers has been validated by the commercial CFD code(Fluent). The efficiency of optimized rake impeller was up to 4.6% higher than the conventional impeller. The more parametric study for high efficiency and good cavitation performance is expected to be conducted in a near future.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.286-304
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• 2017

In this study, we proposed a new-type of circular perforated caisson breakwater consisting of a bundle of latticed blocks that can be applied to a small port such as a fishing port, and numerically investigated the hydraulic characteristics of the breakwater. The numerical method used in this study is OLAFOAM which newly added wave generation module, porous media analysis module and reflected wave control module based on OpenFOAM that is open source CFD software published under the GPL license. To investigate the applicability of OLAFOAM, the variations of wave pressure acting on the three-dimensional slit caisson were compared to the previous experimental results under the regular wave conditions, and then the performance for irregular waves was examined from the reproducibility of the target irregular waves and frequency spectrum analysis. As a result, a series of numerical simulations for the new-type of circular perforated caisson breakwaters, which is similar to slit caisson breakwater, was carried out under the irregular wave actions. The hydraulic characteristics of the breakwater such as wave overtopping, reflection, and wave pressure distribution were carefully investigated respect to the significant wave height and period, the wave chamber width, and the interconnectivity between them. The numerical results revealed that the wave pressure acting on the new-type of circular perforated caisson breakwaters was considerably smaller than the result of the impermeable vertical wall computed by the Goda equation. Also, the reflection of the new-type caisson breakwater was similar to the variation range of the reflection coefficient of the existing slit caisson breakwater.