• Proceeding of EDISON Challenge
• /
• 2013.04a
• /
• pp.343-348
• /
• 2013

초임계 익형은 천음속 영역에서 비행하는 상업용 민간 항공기와 전투기 날개의 공력성능을 향상시키기 위해 Whitcomb R. T.가 제안 하였다. 초임계 익형은 상부표면을 평평하게 디자인하여 임계마하수보다 큰 마하수에서 나타나는 익형 주위의 충격파 출현을 지연시킴으로써 항력을 줄일 수 있고, 상부 표면의 평면 설계로 인한 양력 감소를 보정하기 위하여 하부 표면의 꼬리부분에 캠버가 있는 형상을 하고 있다. 본 연구에서는 EDISON CFD를 이용하여, 초임계 익형의 공력특성을 해석하고 Xfoil의 data와 비교 분석하였다. 또한, 초임계 익형의 형상을 변경하여 두께와 뒷전 캠버가 다른 초임계 익형을 설계하였다. 새로운 초임계 익형의 형상은 상용 프로그램 Maple12을 이용하여 Whitcomb Integral Supercritical Airfoil의 형상을 수정하여 구할 수 있다. 초임계 익형 주위의 유동을 2D압축성 유동으로 가정하고 EDISON CFD의 2D_Comp-2.0 솔버를 사용하여 수치해석을 수행하였다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.12
• /
• pp.1489-1495
• /
• 2013

High-pressure flows are ubiquitous in many industrial fields. A representative application is fuel injection using a common-rail control system in diesel engines, where the injection pressure in the injector exceeds 1000 bar. In high-speed injection, the fluid injected through the nozzle undergoes breakup owing to the interaction with the ambient gas. The breakup process influences mixture formation, which in turn influences combustion in diesel engines. Therefore, it is very important to analyze the breakup process of fuel spray. The Reitz and Diwakar model and cascade atomization and breakup (CAB) model were used in this study as sub-models for the numerical analysis of the breakup process of fuel spray. This study aims to precisely analyze the breakup process of spray and to investigate the breakup frequency of the injected fuel. Consequently, it proposes a suitable sub-model for analyzing the breakup process of a diesel spray by using CFX, a commercial CFD program.

• Journal of Korea Society of Industrial Information Systems
• /
• v.29 no.1
• /
• pp.117-123
• /
• 2024

Bubbles generated in water receive an upward buoyant force due to the density and pressure difference of the surrounding fluid. Additionally, the behavior, shape, and heat exchange process of bubbles vary depending on the viscosity, surface tension, rising speed, and size difference with the surrounding fluid. In this study, we modeled speed, and heat transfer of a high-temperature single bubble rising in a cylindrical water tank. For this purpose, velocity, and temperature of the bubbles were calculated using theoretical equations, to be compared with numerical simulation results. The numerical analysis was performed using a commercial software, and the stability of the numerical analysis with mesh size was confirmed through calculation of the grid convergence index. The numerical analysis of the rising speed and temperature of a single bubble showed the values to converge when the minimum cell size was 1/160 of the bubble diameter, and the temperature decrease was confirmed to be the same as that of the surrounding fluid within 0.05 seconds.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.36 no.4
• /
• pp.259-264
• /
• 2023

In this study, we devised a parametric analysis workflow for efficiently analyzing the material properties of 3D woven materials. The parametric model uses wire spacing in the woven materials as a design parameter; we generated 2,500 numerical models with various combinations of these design parameters. Using MATLAB and ANSYS software, we obtained various material properties, such as bulk modulus, thermal conductivity, and fluid permeability of the woven materials, through a parametric batch analysis. We then used this large dataset of material properties to perform a regression analysis to validate the relationship between design variables and material properties, as well as the accuracy of numerical analysis. Furthermore, we constructed an artificial neural network capable of predicting the material properties of 3D woven materials on the basis of the obtained material database. The trained network can accurately estimate the material properties of the woven materials with arbitrary design parameters, without the need for numerical analyses.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.41 no.8
• /
• pp.553-561
• /
• 2017

The main motivation for this study was to establish a CFD-based procedure for the analysis of heating characteristics, particularly in industrial furnaces. As certain open-source software packages have gained popularity in dealing with complex industrial problems, the OpenFOAM framework was selected for further development of advanced physical models to meet industrial requirements. In this study, the newly developed comprehensive model was applied to simulate physical processes in the full-scale horizontal furnace of a continuous galvanizing line (CGL). The numerical results obtained indicate that the current approach predicts heating characteristics reasonably well. It was also found that radiative heat transfer plays a dominant role in heating the moving strip. To improve the predictability of our method, further work is required to model the turbulence-chemistry interaction realistically, as well as to impose a physically correct thermal wall boundary condition.

• Journal of the Korean Vacuum Society
• /
• v.17 no.3
• /
• pp.189-194
• /
• 2008

Measurements with a Langmuir probe, which are the most often used procedures of plasma diagnostics, can disturb plasma flows and change its characteristics quite a little because the probe should be inserted into thermal flowing plasmas. In this study, we calculated the characteristics of thermal plasmas with and without the probe into an atmospheric argon free-burning arc numerically, and investigated aerodynamic and thermal disturbances with temperature and axial velocity distributions. For the modelling of thermal plasmas, we have made two governing equations, which are on the thermal-flow and electromagnetic fields, coupled together with a commercial CFD package and user-coded subroutines. It was found that thermal disturbances happened to both sides of the probe, before and behind, seriously. Due to the aerodynamic disturbance, we could find that there were the stagnation point in front of the probe and the wake behind it. Therefore, aerodynamic and thermal disturbances caused by the probe insertion should be considered to increase the reliability of the probe diagnostics.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.33 no.5
• /
• pp.331-338
• /
• 2020

In this study, the characteristic of a 3-D micro-woven material, which is one of the newly developed periodic open-cell structure, is analyzed through various computational simulations. To increase the accuracy of the numerical simulations, the distance between each directional wire is parameterized using six design variables, and its model geometry is precisely discretized using tetrahedron elements. Using the improved computational model, the material properties of the mechanical, thermal, and fluidic behavior are investigated using commercial software and compared with the previous experimental results. By changing the space between the x- and y-directional wires, a parametric test is performed to determine the tendency of the change in the material properties. In addition, the correlation between two different material properties is investigated using the Ashby chart. The result can further be used in determining the optimal pattern and wire spacing in 3-D micro-woven materials.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 2008.04a
• /
• pp.179-186
• /
• 2008

현재 대부분의 산업용 열기관은 효율을 높이기 위하여 연소에 사용되는 공기를 예열하는 방법을 사용한다. 하지만, 산업용 열기관에서 평균적으로 발생되는 $1000^{\circ}C$ 이상의 배기가스는 일반 금속 열교환기에는 적합하지 않다. 이에 반해 세라믹 열교환기의 경우 고온에서 견디는 장점이 있다. 본 연구에서는 기본적인 열교환기 설계 이론을 이용하여 설계프로그램을 제작하였다. 또한 세라믹 열교환기 내 열 유체 거동을 CFD 상용코드인 FlUENT 6.2를 이용한 전산해석을 수행하여 설계결과를 비교 검증하였다. 설계 결과에서 휜의 형태 변화에 따라 열전달율과 온도구배는 무시할 수 있을 정도로 작았으나, 압력강하는 크게 변동되는 결과가 도출되었다. 제한된 모듈 크기에서 휜 간거리는 휜의 두께에 비해 약 3배 이상 클 경우가 적당하며, 판(plate)의 두께는 작을수록 압력손실이 적고, 열전달율이 상승하지만 두께가 너무 얇게 된다면 제작상의 어려움이 생긴다. 향후 연구에서는 단순한 구조에서 벗어나 off-set이나 판형구조를 고려하여 설계함으로서 열전달 면적을 넓히거나 난류유동을 발생시켜 열전달율을 높이는 연구를 진행 할 필요가 있다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.291-291
• /
• 2011

플라즈마에 노출된 재료 표면의 온도 증가는 다음과 같은 요인에 의해서 결정된다. 이온의 충돌에 의한 역학적 에너지, 이온의 중성화, 라디칼의 안정화에 의한 에너지 방출(잠열, latent heat), 플라즈마에서 방출된 빛의 흡수. 이중 식각을 위한 기판 바이어스에 의해서 주로 결정되는 이온 충돌 에너지와 잠열의 방출이 300 mm wafer용 유도 결합 플라즈마 식각 장치에서 소스 전력과 바이어스 전력에 따라서 어떻게 변화하는지 전산 유체 역학 모사 프로그램인 CFD-ACE를 이용하여 상용 식각 장비인 AMAT사의 DPS II를 대상으로 온도 분포의 변화를 계산하였다. 실험 결과와 비교를 위하여 다섯 곳에(상, 하, 좌, 우, 중심) 열전대를 부착한 온도 측정 웨이퍼를 기판의 위치에 설치하고 여러 가지 실험 조건에 대해서 온도의 변화를 측정하였다. Ar 10 mTorr에서 2열 병렬 안테나의 전력을 300 W에서 시간에 따른 온도의 변화를 측정하였다. 이때 wafer의 평균 온도는 $28.9^{\circ}C$에서 $150^{\circ}C$까지 12분 내에 상승하였으며 최고 온도에 도달한 다음에는 거의 일정하게 유지 되었다. Si의 식각에서 온도의 영향을 가장 크게 받는 반응은 F 라디칼에 의한 Si의 직접 식각이며 Arrhenius 식의 형태로 표현하면 0.116*exp (-1250/T)의 형태로 된다. 문헌에 보고된 계수를 이용해서 $29^{\circ}C$의 식각 속도와 플라즈마에 의한 가열 최고 온도인 $150^{\circ}C$ 때의 값을 비교해보면 3.3배의 차이가 난다. 따라서 4%내의 식각 균일도를 목표로 하는 폴리 실리콘 게이트 식각 장비의 설계에서는 플라즈마에 의한 가열 불균일을 상쇄 할 수 있는 히터와 냉각 구조의 최적 설계가 필요하다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2010.11a
• /
• pp.386-392
• /
• 2010

The multiphase simulation of a liquid jet in a lab-scale ramjet combustor with a plain orifice type injector was studied with a commercial CFD tool, a FLUENT program. The objectives of the current study are to analysis the breakup characteristics of a hexane liquid jet in a cross flow and to derive the correlation between flow conditions and drag force coefficients in a test section. From the result of a numerical simulation, we concluded that a DPM and Realizable $k-{\varepsilon}$ model with an enhanced wall treatment were available to simulate the multiphase flow simulation. And the calculated distribution of a hexane vapor concentration was well-matched with experimental results.