• 한국환경과학회지
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• 제29권3호
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• pp.299-306
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• 2020

This study analyzed the changes in the concentrations of the pollutants of constructed treatment wetlands which come from the discharge water of a sewage treatment plant. According to the results of budgets in constructed wetlands, the net production of the organic carbon, nitrogen and phosphorus were 368 kgC/month, 306 kgN/month and -49 kgP/month, respectively. The high particle form of pollutants are mostly removed due to settlement and absorption when passing through wetlands, but because a low processing efficiency for pollutants was shown when sewage treatment plant wastewater flows in, there is a need for a water management system that can reduce the organic matter load through monitoring. The low removal efficiency of constructed wetlands were caused by both structural and operational problems. Therefore, to enable to play a role as a reduction facility of pollutants, an appropriate design and operation manuals for constructed wetlands is urgently needed.

• 융복합기술연구소 논문집
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• 제4권1호
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• pp.37-41
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• 2014

For the analysis of lifting surface at high angle of attack, a Nonlinear Vortex Lattice Method(NLVLM) was used. The NLVLM is intented to compute the interactions between lifting surfaces and separated vertical flow. The lifting surfaces are represented by a lattice of discrete vortex rings. And wakes are represented by families of non-lintersecting, semi-infinite vortex line segments. The image method also used to analyze the ground effect. It is found that vortex lines separated from lifting surfaces represent the separated flows successfully. Although the present method is applied for the rectangular wing and delta wing, extensions can be possible for the arbitrary lifting surfaces. The Present results show good agreement with experimental data.

• 한국분무공학회지
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• 제3권2호
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• pp.42-50
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• 1998

The effect of swirl flows un the fuel spray characteristics were investigated for various swillers in a model combustor. The interaction between the flow field and fuel spray in the main combustion tone made by frontal devices including fuel injection nozzles and swirlers. which were characterized by flow velocities, fuel droplet sizes and their distributions which were measured by APV(Adaptive Phase/Doppler Velocimetry) under atmospheric condition at 320cc/min kerosine fuel flow and 0.04kg/sec air supply. A dual swirler with circumferential two-stage swirl vanes of $40^{\circ}\;and\;45^{\circ}$ vanes in different directions and two single-stage swillers of $40^{\circ}$ vanes with 12 and 16 vanes were tested. It was found that the dual swirler has the largest recirculating zone with highest reverse flow velocity. The strongest swirl flow was found at the boundary of recirculation zone. Small fuel droplets were observed in the main axial stream and inside the recirculation zone when swirling flow field were generated by the frontal devices. These findings could give the tips on the optimal design of frontal devices to realize low emissions in gas turbine combustion.

• 대한기계학회논문집B
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• 제29권8호
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• pp.948-955
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• 2005

A three-dimensional computation was conducted to understand effects of the inlet boundary layer thickness on the internal flow in a low-speed axial compressor operating at the design condition($\phi=85\%$) and near stall condition($\phi=65\%$). At the design condition, the flows in the axial compressor show, independent of the inlet boundary layer thickness, similar characteristics such as the pressure distribution, size of the hub comer-stall, tip leakage flow trajectory, limiting streamlines on the blade suction surface, etc. However, as the load is increased, the hub corner-stall grows to make a large separation region at the junction of the hub and suction surface for the inlet condition with thick boundary layers at the hub and casing. Moreover, the tip leakage flow is more vortical than that observed in case of the thin inlet boundary layer and has the critical point where the trajectory of the tip leakage flow is abruptly turned into the downstream. For the inlet condition with thin boundary layers, the hub corner-stall is diminished so it is indistinguishable from the wake. The tip leakage flow leans to the leading edge more than at the design condition but has no critical point. In addition to these, the severe reverse flow, induced by both boundary layer on the blade surface and the tip leakage flow, can be found to act as the blockage of flows near the casing, resulting in heavy loss.

• 대한기계학회논문집B
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• 제24권6호
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• pp.785-791
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• 2000

GDI (Gasoline Direct Injection) engines are considered as one of the candidates for next generation engines of passenger cars, which reduce exhaust emissions and fuel consumption. In GOI engines, a high-pressure gasoline supply system is required to directly inject the fuel to combustion chambers. Because of low lubricity of gasoline fuel, the clearance between a plunger and a barrel in GDI fuel pumps is too wide to achieve smooth hydrodynamic lubrication. Thus, it is difficult to generate high-pressure condition in GDI fuel pump since large amount of leakage flow occurs between the plunger and the barrel In this study, an optimum plunger design is presented to minimize leakage in the aspect of flow control. This paper analyzes leakage flow characteristics in the clearance to improve pumping performance of GDI fuel pumps. Effects of groove in the plunger are studied according to variations of depth and width. Evaluations of pumping performance are determined by the amount of pressure drop in the leakage path assuming a constant leakage flows. Both of turbulence and incompressible models are introduced in CFD (Computational Fluid Dynamics) analysis. Design parameters have been introduced to minimize leakage in limited space, and a methodological study on geometrical optimization has been conducted. As results of CFD analysis in various geometrical cases, optimum groove depths have been found to generate maximum sealing effects on gasoline fuel between the plunger and the barrel. This procedure offers a methodological way of an enhancement of plunger design for high-pressure GDI fuel pumps.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.485-490
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• 2000

This paper dipicts the computational results for the axisymmetric subsonic/sonic ejector systems with a second throat. The numerical simulations are based on a fully implicit finite volume scheme of the compressible Reynolds-Averaged Navier-Stokes equation in a domain that extends form the stagnation chamber to the ejector diffuser exit. In order to obtain practical design factors for subsonic/sonic ejector systems, the ejector throat area, the mixing section configuration, and the ejector throat length were changed in computations. For the subsonic/sonic ejector systems operating in the range of low operation pressure ratio, the effects of the design factors on the flow are discussed.

• 대한기계학회논문집B
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• 제25권2호
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• pp.269-276
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• 2001

This paper dipicts the computational results for the axisymmetric subsonic/sonic ejector systems with a second throat. The numerical simulations are based on a fully implicit finite volume scheme of the compressible Reynolds-Averaged Navier-Stokes equation in a domain that extends from the stagnation chamber to the ejector diffuser exit. In order to obtain practical design factors for subsonic/sonic ejector systems, the ejector throat area, the mixing section configuration, and the ejector throat length were changed in computations. For the subsonic/sonic ejector systems operating in the range of low operation pressure ratio, the effects of the design factors on the flow are discussed.

• Wind and Structures
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• 제36권4호
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• pp.277-292
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• 2023

Low-rise structures are generally immersed within the roughness layer of the atmospheric boundary layer flows and represent the largest class of the structures for which wind loads for design are being obtained from the wind standards codes of distinct nations. For low-rise buildings, wind loads are one of the decisive loads when designing a roof. For the case of cylindrical roof structures, the information related to wind pressure coefficient is limited to a single span only. In contrast, for multi-span roofs, the information is not available. In this research, the numerical simulation has been done using ANSYS CFX to determine wind pressure distribution on the roof of low-rise cylindrical structures arranged in rectangular plan with variable spacing in accordance with building width (B=0.2 m) i.e., zero, 0.5B, B, 1.5B and 2B subjected to different wind incidence angles varying from 0° to 90° having the interval of 15°. The wind pressure (P) and pressure coefficients (C_pe) are varying with respect to wind incidence angle and variable spacing. The results of present numerical investigation or wind induced pressure are presented in the form of pressure contours generated by Ansys CFD Post for isolated as well as variable spacing model of cylindrical roofs. It was noted that the effect of wind shielding was reducing on the roofs by increasing spacing between the buildings. The variation pf Coefficient of wind pressure (C_pe) for all the roofs have been presented individually in the form of graphs with respect to angle of attacks of wind (AoA) and variable spacing. The critical outcomes of the present study will be so much beneficial to structural design engineers during the analysis and designing of low-rise buildings with cylindrical roofs in an isolated as well as group formation.

• KIEAE Journal
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• 제9권3호
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• pp.61-68
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• 2009

Gwangju Metropolitan Government & Ministry of Environment have signed a model city in response to Climate Change agreement. The agreement calls for Gwangju to cut greenhouse gas emissions 10% below 2005 levels by 2015. Gwangju has seen this agreement as an opportunity to cut pollution and conserve the environment as well as to reinvigorate local economy. According to policy of Gwangju, Gwangju held design competition for Gwangju City Arboretum on march, 2009. The purpose of design competition was to give a wide publicity to Gwangju as Hub City of Asian Culture and construct carbon-neutral arboretum in accordance with the policy of 'Low-Carbon and Green Growth'. First of all, a design concept of arboretum is 'winding, round, overlay 'to reflect the landscape of Nam-do which is surrounded by mountains and river flows through the village. Second, the arboretum has five different places with these themes - Forest of Festivals, Health, Nature, Nostalgia, Education and Future. Each place has a symbolic theme park and different flow planning respectively. Third, the most critical point is that the arboretum is a carbon-neutral park. Gwangju arboretum will soon be developed in metropolitan sanitary landfill and constructed as the O2 arboretum based on low carbon strategy. Fourth, the O2 arboretum suggests specialized issue : 'Energy Saving', 'Recycling System', 'Green Network', 'Water System(rainwater maintenance and wetland development)'. Besides, main buildings(greenhouse, visitor center, Nam-do experience exhibition hall, and forest museum) is designed in consideration of harmony with topography character, surroundings. Also, planting will be a multilayer plant based on native landscape trees in consideration of function and the growth characteristics.

• 한국유체기계학회 논문집
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• 제19권2호
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• pp.21-26
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• 2016

The objective of present study is to assess the performance of the first stage compressor in a total 3-stage 5000 HP-level turbo compressor. CFD commercial code, CFX has been used to predict three-dimensional flow characteristics inside of the impeller. Shear Stress Transport (SST) model has been used to simulate turbulent flows through Reynolds-averaged Navier-Stokes (RANS) equations. Grid dependency has been also checked to get optimal grid distribution. Numerical results have been compared with the experimental test results to elucidate performance characteristics of the present compressor. In addition, flow characteristics of the impeller only have been studied for various blade configurations. Angular offset in leading edge of the blade has been selected for the optimal blade design. Performance characteristics in region of low mass flow rate and high pressure ratio between the impeller entrance and exit have been investigated for the selection of optimal blade design. Also, flow instability such as stall phenomena has been studied and anti-stall characteristics have been checked for various blade configurations in the operational window.