• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.3
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• pp.8-16
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• 2014

This paper analyzes the effects of sideslip angle(SA) on the buzz margin of supersonic intake. The buzz margin is assumed to be stabilized by a controller which generates command depending only on the longitudinal sensor measurements. The analysis is performed based on three dimensional CFD results with which the sensor measurements can be simulated. In such a control system based on the longitudinal measurements, unexpected lateral flow perturbation results in the increase in the total angle of attack(TAoA), that causes the degradation of the engine intake performance. As a consequence, it is shown that the control stability is reduced such that additional control margin needs to be secured.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2003.05a
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• pp.601-604
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• 2003

본 연구의 목표는 현재 복수기의 운전상황을 반영한 열유동 해석을 수행하여 저압터빈후드 온도의 좌우 편차가 발생하는 원인을 분석하는 것이다. 그러나 실제 복수기가 기하학적 형상이 복잡하고, 운전조건의 명확한 설정이 어려우며, 또한 수치해석에도 포함되는 오차 등을 고려하면, 단순히 현재의 운전조건 만을 반영한 해석에 의하여서는 원인의 규명이 어렵게 된다.(중략)

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.321-326
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• 2013

본 연구에서는 원형실린더의 강제 수평 및 수직진동에 따른 와흘림을 관찰하였다. EDISON_CFD의 가상경계법을 이용하여 원형실린더 주위 유동현상을 수치 모사하였다. 원형실린더의 강제 진동 특성에 따른 와흘림 진동수, 공력계수 등의 영향을 분석하였다. 특히, 진동방향에 따른 와흘림의 영향을 분석하여, 원형실린더의 강제 진동에 따른 유동의 선형성을 평가하였다.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.75-75
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• 2011

본 논문에서는 진동중인 교량 거더에 작용하는 풍하중을 산정하고 그에 따른 플러터 발생풍속을 예측하기 위하여 분산형 전산환경을 활용한 수치해석 연구를 수행하였다. 분산형 전산환경은 웹 포탈을 기반으로 수치해석 환경을 제공하는 수치풍동 시스템으로서, 전산유체역학(CFD : Computational Fluid Dynamics)에 대한 전문지식이 부족한 사용자들도 격자생성, 수치해석자를 이용한 계산, 가시화 등의 전 과정을 편리하게 수행할 수 있는 차세대 토목분야 연구 환경이다. 본 시스템은 그리드스피어(GfidSphere)를 기반으로 구성되었으며, 기본적으로 사용자 관리, 세션 관리, 그룹 관리, 레이아웃 관리 등을 제공하여 사용자가 포탈을 통해서 다양한 서비스를 쉽게 사용할 수 있는 환경을 구축하도록 도와준다. 수치해석을 위한 유체 지배방정식은 2차원 비정상 비압축성 RANS(Reynolds-Averaged Navier-Stokes) 방정식이며, pseudo compressibility 방법을 적용하였다. 비정상 유동장을 해석하기 위하여 이중시간 전진법(dual time stepping)을 사용하였으며, 수렴가속화를 위해 Multi-grid 기법을 적용하였다. 또한 난류 유동장 해석을 위해서 $k-{\omega}$ SST 난류 모델을 사용하였으며, 난류 천이 과정에서의 유동을 모사하기 위하여 Total stress limitation 방법을 적용하였다. 교량 거더의 연직과 회전방향의 2자유도 움직임을 모사하기 위하여 동적격자 기법을 도입하였다. 교량 거더 주변의 비정상 유동해석 결과를 통해, 거더 표면에서 떨어져나가는 크고 작은 와류의 영향으로 양력 및 모멘트 계수 그래프가 중첩된 진폭과 주기를 갖고 주기적으로 나타나는 것을 확인할 수 있었다. 또한 계산된 비정상 공기력을 적용한 2자유도 플러터 방정식을 통하여 플러터 발생풍속을 산정하였다. 최종적으로 본 연구에서 계산된 결과의 타당성을 검증하기 위하여 수치적으로 구한 플러터 발생풍속과 기존의 실험 및 수치해석 결과를 비교하였으며, 결과는 잘 일치하였다.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1337-1345
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• 2007

The present study is a basic investigation for systematically proceeding disaster prevention studying the effect of platform screen door in case of fire at the subway station. In the paper, the characteristics of screen door were surveyed and described. The fully closed platform screen door and the island type of subway station were employed for simulation-study. Numerical simulations of fire driven flow at the subway station with platform screen door were performed with commercial fire CFD code. For analyzing of the effect of platform screen door, the fire simulations with and without the platform screen door were compared. For the fire location, the one is located on the platform and the other case on the railway. The Ultrafast model was taken as fire growth scenario. The maximum heat release rate was 10MW. The propagated time of the heat and smoke to stairs was within 4 minute when the fire is located on the platform. However the heat and smoke propagation was block off by screen door when the fire is located on the railway.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.18-25
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• 2005

In this study, the main focus is the simulation of acoustic wave scattering in trailing edge and the analysis of the generation mechanism of instability wave by the interaction of trailing edge, shear flow and initial disturbance. The numerical algorithm is based on CFD/CAA hybrid method with high-order computational aeroacoustic method. It is found that steady mean flow gradient terms play a crucial role on the generation of instability wave through the comparison of simulations of Simple Linearized Euler Equation and Full Linearized Euler Equation. Through the comparison with the results of Full Navier-Stokes Equation, it is reasonable and efficient to use the Full Linearized Euler Equation in the initial generation mechanism of the instability wave near the trailing edge.

• Transactions of the Korean hydrogen and new energy society
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• v.10 no.2
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• pp.107-118
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• 1999

A 5-kW MCFC stack with $3,000cm^2$ electrode area was tested to investigate cell performance and operation characteristics. The stack performance was evaluated based on electrical output and I-V change. The stack showed high cell performance (7.6 kW) than the design performance and operated for more than 5,760 hours, but a significant temperature gradient inside the stack was observed. A 3-dimensional mathematical model for molten carbonate fuel cell (MCFC) was developed for the purpose of simulation of stack performance during the operation. The model was solved using PHOENICS, a computational fluid dynamics (CFD) code. The simulation result demonstrated a close prediction of the temperature gradient and stack performance.

• Elastomers and Composites
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• v.41 no.4
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• pp.223-230
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• 2006

Rubber compounds have a high viscoelastic property. One of the viscoelastic behaviors during profile extrusion is the swelling of extrudate, and the amount of swelling varies with operational conditions in extrusion. It is well recognized that the elastic portion in the viscoelastic property plays an important role in the extrudate swell. In this study computer simulation of the die swell at the capillary die for several rubber compounds has been performed using commercial CFD code, Polyflow. A non-linear differential viscoelastic model, Phan-Thien-Tanner (PTT) model, was used in the computer simulation. Non-isothermal behavior was considered in the calculation. Distribution of pressure, velocity and temperature in the reservoir and capillary die, and extrudate profiles were predicted through the simulation. The amount of the die swell fur the different rubber compounds was investigated for various flow rates and three types of length to diameter of the capillary die. It is concluded that the PTT model successfully represented viscoelastic behavior of rubber compounds.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.15-23
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• 2019

In this study, an extinguishment model of a three-dimensional solid propellant rocket was developed by combustion and fast depressurization to control the thrust of a solid rocket. Computational fluid dynamics simulation was carried out to ascertain the change in flow patterns in the combustion chamber and the extinguishment process by using a pintle. An ammonium perchloride was used as the target propellant and the dynamic behavior of its major parameters such as temperature, pressure, and burning rate was predicted using the combustion model. The dynamic behavior of the combustion chamber was confirmed by fast depressurization from an initial pressure of 7 MPa to a final pressure of 2.5 MPa at a depressurization rate of approximately -912 MPa/s.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.713-722
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• 2022

In this paper, the flow performance and aero-acoustic noise generated by the target centrifugal fan system were investigated numerically and experimentally. Also, the numerical method for Computational Aero-Acoustics were evaluated by comparing each method. To analyze the performance of the centrifugal fan experimentally, the acoustic power level was measured in the semi-anechoic chamber using microphones, and the active frequency range for the noise performance was identified and that frequency range was applied for Computational Aero-Acoustics (CAA) techniques as sampling frequency. Then, Navier-Stokes equation and the Ffowcs Williams&Hawking equations were used to analyze the flow and sound power numerically, respectively, and a virtual acoustic radiation plane was designed and used for the implementation of the sound field. The accuracy and numerical characteristics of the numerical methods were validated by comparing simulated acoustic power levels with acoustic power levels measured.