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항공기 가스터빈용 오일쿨러 해석을 위한 1 차원 열유동 네트워크 수치적 모델 개발 및 연구
김영진(Young Jin Kim),김민성(Minsung Kim),하만영(Man Yeong Ha),민준기(June Kee Min) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.11
항공기용 가스터빈 엔진에 있어서, 기어 어셈블리 및 전자장비에 사용되는 오일의 냉각을 위하여 열교환기가 사용되며 이를 Surface air-oil heat exchanger (SAOHE) 라고 한다. 이 열교환기는 엔진 팬 케이싱 내부에 설치되며 기어박스 시스템 및 전자장비로부터 바이패스 덕트 후류 쪽으로 열을 소산시킨다. 본 연구의 목적은 SAOHE 의 설계를 위한 효율적인 수치해석방법을 개발하는 것이다. SAOHE 설치에 따른 핀에서의 열공력학적 성능을 평가하기 위하여 다공성 모델을 활용한 2 차원 수치해석을 수행하였고, 열교환기 성능평가에 대해 시간 및 비용적으로 효과적인 1 차원 열유동 네트워크 프로그램을 개발하였다. 이 프로그램을 이용하여 열교환기의 압력강하 및 열전달 성능을 예측하였고, 1 차원 열유동 네트워크 프로그램을 검증하기 위해 2 차원 전산해석 결과 및 실험 결과와 비교하였다. In an aero gas-turbine engine, a surface air-oil heat exchanger (SAOHE) is used to cool the oil system for the gearboxes and electric generators. The SAOHE is installed inside the fan casing of the engine in order to dissipate the heat from the oil system into the bypass duct stream. The purpose of this study was to develop an effective numerical method for designing an SAOHE for an aero gas-turbine engine. A two-dimensional model using a porous medium was developed to evaluate the aero-thermal performance of the fins of the heat exchanger, and a one-dimensional flow and thermal network program was developed to save time and cost in the evaluation of the heat exchanger performance. Using this network program, the pressure drop and heat transfer performance of the heat exchanger were predicted, and the results were compared with two-dimensional computational fluid dynamics results and experiment data for validation.
하부 플레넘 구조물 조건을 고려한 클린룸의 편류 개선 방법
김영섭(Young Sub Kim),하만영(Man Yeong Ha) 대한설비공학회 2008 설비공학 논문집 Vol.20 No.1
To achieve the unidirectional airflow in a cleanroom, we need to predict accurately the static pressure losses at the lower plenum and to control properly the opening pressure ratio of access floor panels based on these pressure losses. At first, the present study proposed a correlation to predict the velocity distribution at the lower plenum, because the accuracy to predict pressure losses at the lower plenum depends on how to calculate the velocity correctly against the inner structures at the lower plenum. In the second place, this study proposed correlations which considered the effect of inner structures such as columns, ducts and equipments at the lower plenum on pressure losses. In order to test the accuracy of these correlations, we compared air flow patterns before regulating the opening ratio of access floor with those after regulating. Results after regulating the opening ratio of access floor show good unidirectional uniform airflow pattern. So the present method can be used as an important tool to control the air flow in a cleanroom.
내부 원형 실린더의 크기가 정육면체 밀폐계 내부의 3 차원 자연대류 현상에 미치는 영향
서영민(Young Min Seo),최창영(Changyoung Choi),하만영(Man Yeong Ha),박상후(Sang Hu Park) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.12
본 연구는 정육면체 밀폐계 내부에 존재하는 고온의 원형 실린더의 크기 변화에 따른 밀폐계 내부의 3 차원 자연대류 현상에 대한 수치해석을 수행하였다. 본 연구에서 고려한 Rayleigh 수는 103 부터 105 까지며 Prandtl 수는 0.7 이다. 내부 원형 실린더의 반경은 0.1L 부터 0.4L 범위에서 0.1L 간격으로 변경하였다. 본 연구에서 고려한 모든 Rayleigh 수와 실린더 반경의 범위에서 열유동장은 정상 상태의 특성을 보였다. 내부 원형 실린더의 크기가 증가하여 실린더 표면과 밀폐계 벽면이 가까워 질수록 실린더 표면과 밀폐계 벽면의 평균 Nusselt 수는 증가하였다. 내부 원형 실린더의 크기 변화에 따른 정육면체 밀폐계 내부의 자연대류 현상은 온도장, 유동장 및 표면 평균 Nusselt 수의 분포를 바탕으로 분석하였다. This study evaluates the effect of a heated circular cylinder"s size on three-dimensional natural convection in a cubical enclosure. The Rayleigh number was varied between 103 and 105, and the Prandtl number was maintained at 0.7. In this study, the radius of the circular cylinder was changed by 0.1 L within a range of 0.1.0.4 L. The thermal and fluid flow characteristics were regarded to be independent of time in the range of the Rayleigh number and cylinder radius considered in this study. The surface-averaged Nusselt numbers of the cylinder and the enclosure were found to increase with the increase in the radius of the cylinder. The effect of the cylinder"s size on natural convection in the enclosure was analyzed across the thermal and flow fields, and the distributions of the Nusselt numbers.
김영주(Young Joo Kim),윤현식(Hyun Sik Yoon),하만영(Man Yeong Ha) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
In the present study, the effect of striped pattern rate of hydrophobic surface and hydrophilic surface on skin-friction drag are investigated through direct numerical simulations of turbulent channel flow. The slip length is 0.005, normalized by channel half width. Slip velocities and wall shear stresses are determined for variety of super-hydrophobic surface and micro-feature geometry configurations at friction Reynolds number of Reτ=180. When the SP (striped pattern) boundary condition is used in the streamwise direction, the skin-friction drag decreases, but the rate of drag reduction is smaller than hydrophobic surface which has common slip length. The rate of SP used is 1 to 6, the effect of SP surface rate has an interrelationship on drag reduction.
2 차원 채널 내부에서 자유 낙하하는 정사각형 입자의 운동에 관한 수치적 연구
최창영(Chang Young Choi),윤현식(Hyun Sik Yoon),하만영(Man Yeong Ha) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
This paper presents a numerical investigation of the characteristics of flow around a square particle freely falling in a two-dimensional channel. The FSI (fluid-solid interaction) has been realized by using the directforcing fictitious domain (DF/FD) method. In order to identify the effect of fluid properties on the flow characteristics and solid motion by FSI, two different densities and especially, a various range of the fluid viscosity have been considered. In addition, the off-centered distance as the initial position of the square particle has been imposed to research the effect of the gap between the channel wall and the square particle. Quantitative information about the drag coefficient on the square particle is highlighted.