• 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 Propulsion Engineers
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• v.12 no.1
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• pp.51-56
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• 2008

In this work the realistic install performance analysis of a helicopter was performed together with power extraction enabling to operate auxiliary system as well as intake pressure loss, loss due to bleed air, etc. which must be considered in practical propulsion system's performance modelling to be installed to the airframe. The pressure loss occurring in intake was estimated from the intake performance map with relationships of Mach Number and pressure loss. In order to evaluate the proposed installed performance model, the experimental data for comparison must be needed when mounted in propulsion system. However because of lack of accessibility to such real data at the moment, the alternative way was made through comparison that the analysis results by the proposed model were compared with a wellknown commercial program GASTURB's analysis results. The validity of the proposed installed performance model was consequently confirmed because its average deferences from the GASTURB's results were within 0.5%.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.6
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• pp.764-772
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• 2016

This paper presents on the evaluation of numerical analysis model of a ball valve used for a gas pipeline. The ball valve has important role to control the gas flow of the pipeline as well as safety operation to prevent gas explosion at the emergency. For the validation of numerical simulation, the computational domains are introduced three different types: a hexahedron chamber connected to a pipeline outlet without considering the geometry of pressure tubes, a pipeline only considered the geometry of pressure tubes, and a pipeline connected both of the a hexahedron chamber and pressure tubes. The commercial code, SC/Tetra, is introduced to solve the three-dimensional steady-state Reynolds-averaged Navier-Stokes analysis in the present study. The valve flow coefficient and valve loss coefficient with respect to the valve opening rate of 30%, 50%, and 70% are compared with experimental results. Throughout the numerical analysis for the three analysis domains, pressure computed along the pipeline is affected by computational domains. It is noted pressure obtained by the computational model considering both of the a hexahedron chamber and pressure tubes has a relatively good agreement to the experimental data.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.1
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• pp.1-9
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• 2021

In the present study, the model-scale Propeller Open Water (POW) tests for the propeller of 176K bulk carrier and 8600TEU container ship were conducted through Computational Fluid Dynamics (CFD) simulation. In order to solve the incompressible viscous flow field, the Reynolds-averaged Navier-Stokes (RaNS) equations were employed as the governing equations. The γ-Reθ(gamma-Re-theta) transition model combined with the SST k-ωturbulence model was introduced to describe the laminar-turbulence transition considering the low Reynolds number of model-scale. Firstly, the flow simulation developing over a flat plate was performed to verify the transition modeling, in which the wall shear stresses were compared with experiments and other numerical results. Then, to investigate the effect of the model, the CFD simulation for the POW test was performed and the simulated propeller performance was validated through comparison with the experiment conducted at Korea Research Institute of Ships & Ocean Engineering (KRISO).

• Journal of the Korean Society for Environmental Technology
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• v.19 no.6
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• pp.528-535
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• 2018

In this study, the effect of obstacle aspect ratio on vortex in building canyon was numerically investigated using a computational fluid dynamics(CFD) model. The sensitivity experiments were performed in the cases of increasing building length(L) and height(H) by the width(W) of building canyon. The wind vector fields and secondary reverse vortex in building canyon were discussed in this study. For the horizontal vortex, the vortex zone increased as the building length increases, but the vectors at the middle of building canyon began to change in the case of L/W=2.5. In the case of L/W=3.0, the smaller primary vortex was presented with the secondary reverse vortex. For the vertical vortex, the vortex zone increased as the building height increases, but the direction of vectors at the bottom of building canyon began to change in the case of H/W=2.5. In the case of H/W=3.5, the smaller primary vortex was presented with the secondary reverse vortex.

• Journal of the Korea Convergence Society
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• v.12 no.11
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• pp.291-299
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• 2021

Recently, due to environmental problems caused by densification and high rise of urban areas, interests in air flow is increasing and appropriate shape and layout design of buildings is required. Therefore, in this study, we intend to propose an experimental method that can observe the air flow around a building using thermochromic pigment. Thermochromic pigments have limitations in observing precise temperature changes due to the characteristic that the color changes only with respect to a specific temperature, but they have the advantages of easy configuration of experimental equipment and short time required for experiments. In this study, the air flow tendencies around a building was examined by performing CFD analysis for a simple model and then compared with the thermochromic experiment results in order to review the usefulness of the proposed experimental method. As a result of the experiment, it was possible to observe the formation of separated flow and vortex region generated by buildings using the charateristics of thermochromic pigment and it was confirmed that the proposed method can be useful for buildings design and urban city planning.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.417-428
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• 2021

The combustion characteristics of anthracite, which follow a complex process with low reactivity, must be considered through the dynamic behavior of circulating fluidized bed (CFB) boilers. In this study, computational fluid dynamics (CFD) simulation was performed to analyze the combustion characteristics of anthracite in a pilot scale 0.1 MW_th Oxy-fuel circulating fluidized bed (Oxy-CFB) boiler. The 0.1MW_th Oxy-CFB boiler is composed of combustor (0.15 m l.D., 10 m High), cyclone, return leg, and so on. To perform CFD analysis, a 3D simulation model reactor was designed and used. The anthracite used in the experiment has an average particle size of 1,070 ㎛ and a density of 2,326 kg/m³. The flow pattern of gas-solids inside the reactor according to the change of combustion environment from air combustion to oxygen combustion was investigated. At this time, it was found that the temperature distribution in air combustion and oxygen combustion showed a similar pattern, but the pressure distribution was lower in oxygen combustion. addition, since it has a higher CO₂ concentration in oxygen combustion than in air combustion, it can be expected that carbon dioxide capture will take place actively. As a result, it was confirmed that this study can contribute to the optimized design and operation of a circulating fluidized bed reactor using anthracite.

• Clean Technology
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• v.21 no.3
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• pp.191-199
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• 2015

The SO_x emission from the ship diesel engines will do a negative influence to the human health and the environment. To reduce the negative environmental effect of the SO_x emission caused by the high traffic of ship movements, the SECA (SO_x emission control area) has been set on several province around world to carry out the severe emissions control and to meet the emissions control standard. To cut down the SO_x emission from the ships, the wet type scrubber is being used widely. In this work, we prepared a numerical model to simulate the spray type scrubber to study the motion of liquid droplets in the flow of the scrubber. For the analysis, the CFD (computational fluid dynamics) method was adopted. As a special topic of the study, we designed the wave plate type of mist eliminator to check the carry over of the uncontrolled water droplet to the exhaust. Numerical analysis is divided into two stages. At the first stage, the analysis was done on the basic scrubber without the mist eliminator, and then the second stage of analysis was done on the scrubber with the mist eliminator on several condition to check and compare with the basic scrubber. On the condition of the basic scrubber, 42.0% of the distributed water droplets were carried over to the exhaust. But by adding the designed droplet eliminator at the exhaust of the scrubber, only 3.4% of the distributed water droplets supplied to the scrubber was emitted to the atmosphere.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.5
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• pp.323-334
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• 2020

Since boundary layer transition has a significant impact on the aero-thermodynamic performance of hypersonic flight vehicles, capability of accurate prediction of transition location is essential for design and performance analysis. In this study, γ-Re_θt model is improved to predict transition of hypersonic boundary layers and validated. A coefficient in the production term of the intermittency transport equation that affects the transition onset location is constructed and applied as a function of Mach number, wall temperature, and freestream stagnation temperature based on the similarity numerical solution of compressible boundary layer. To take into account a Mach number dependency of transition onset momentum thickness Reynolds number and transition length, additional correlation equations are determined as function of Mach number and applied to Re_θc and F_length correlations of the baseline model. The suggested model is implemented to a commercial CFD code in consideration of practical use. Analysis of hypersonic flat plate and circular cone boundary layers is carried out by using the model for validation purpose. An improvement of prediction capability with respect to variation of Mach number and unit Reynolds number is identified from the comparison with experimental data.

• Korean Journal of Remote Sensing
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• v.36 no.6_3
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• pp.1643-1652
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• 2020

To investigate the characteristics of detailed flows in a building-congested district, we coupled a computation fluid dynamics (CFD) model to the local data assimilation and prediction system (LDAPS), a current operational numerical weather prediction model of the Korea Meteorological Administration. For realistic numerical simulations, we used the meteorological variables such as wind speeds and directions and potential temperatures predicted by LDAPS as the initial and boundary conditions of the CFD model. We trilinearly interpolated the horizontal wind components of LDAPS to provide the initial and boudnary wind velocities to the CFD model. The trilinearly interpolated potential temperatures of LDAPS is converted to temperatures at each grid point of the CFD model. We linearly interpolated the horizontal wind components of LDAPS to provide the initial and boundary wind velocities to the CFD model. The linearly interpolated potential temperatures of LDAPS are converted to temperatures at each grid point of the CFD model. We validated the simulated wind speeds and directions against those measured at the PKNU-SONIC station. The LDAPS-CFD model reproduced similar wind directions and wind speeds measured at the PKNU-SONIC station. At 07 LST on 22 June 2020, the inflow was east-north-easterly. Flow distortion by buildings resulted in the east-south-easterly at the PKNU-SONIC station, which was the similar wind direction to the measured one. At 19 LST when the inflow was southeasterly, the LDAPS-CFD model simulated southeasterly (similar to the measured wind direction) at the PKNU-SONIC station.