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내부에 원형 실린더가 존재하는 기울어진 정사각형 밀폐계 내부의 자연대류 현상에 Prandtl 수가 미치는 영향
문기수(Gisu Mun),두정훈(Jeonghoon Doo),하만영(Man Yeong Ha) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Two-dimensional numerical analysis were conducted to investigate the effect of Prandtl number on the natural convection in a cold outer tilted square enclosure with an inner hot circular cylinder for different Prandtl numbers (10-2≤Pr≤102) and Rayleigh numbers (103≤Ra≤106). The numerical solutions are obtained using immersed boundary method to configurate an inner circular cylinder based on the finite volume method. The outer square enclosure is tilted from γ=0˚ to γ=45˚ by each 5 degrees. The effect of the Prandtl number on natural convection in an enclosure is analyzed by the distribution of the streamlines, isotherms and surface-averaged Nusselt numbers.
Prandtl 수 변화가 내부 원형 실린더가 존재하는 기울어진 정사각형 밀폐계 내부의 자연대류 현상에 미치는 영향
문기수(Gi Su Mun),최창영(Changyoung Choi),하만영(Man Yeong Ha),윤현식(Hyun Sik Yoon) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.11
본 연구에서는 내부에 고온의 원형 실린더가 위치한 저온의 기울어진 사각 밀폐계에서 Prandtl 수 변화에 따른 밀폐계 내부 자연대류 현상에 대한 수치해석을 수행하였다. Rayleigh 수가 10<SUP>3</SUP>, 10<SUP>4</SUP>, 10<SUP>5</SUP> 그리고 밀폐계의 각도가 0°, 15°, 30°, 45° 인 경우에 대해서 Prandtl 수를 0.1, 0.7, 7 로 변화시키며 Prandtl 수의 영향을 분석하였다. Prandtl 수의 변화에 따른 밀폐계 내부의 자연대류 현상은 실린더 표면과 밀폐계 벽면의 평균 Nusselt 수, 밀폐계 내부의 등온선 및 유선을 바탕으로 분석되었다. Prandtl 수가 0.7, 7 인 경우에는 각도 및 Rayleigh 수에 관계없이 열유동은 정상상태의 특성을 보였지만 Prandtl 수가 0.1 인 경우에는 Rayleigh 수가 105 이고 밀폐계의 각도가 0° 와 45° 일 때 시간에 따라 열유동장이 변하였다. 실린더 표면과 밀폐계 벽면의 평균 Nusselt 수는 Rayleigh 수가 10<SUP>5</SUP> 인 경우, 각도에 관계없이 Prandtl 수가 클수록 증가하였다. 특히 Rayleigh 수가 10<SUP>5</SUP> 이고 Prandtl 수가 0.1 일 때 밀폐계의 각도가 45° 인 경우 실린더 표면과 밀폐계 벽면의 평균 Nusselt 수가 크게 증가하였다. A numerical analysis of the effect of the Prandtl number on the natural convection in a cold outer tilted square enclosure with an inner hot circular cylinder is presented. Several Prandtl numbers (Pr=0.1, 0.7, 7) are considered, with different angles(0°, 15°, 30°, 45°) for the enclosure and Rayleigh numbers (Ra=10<SUP>3</SUP>, 10<SUP>4</SUP> ,10<SUP>5</SUP>). The effect of the Prandtl number on the natural convection is analyzed using isotherms and streamline and surface-averaged Nusselt numbers. The flow and heat transfer characteristics are found to be dependent on the time for Ra=10<SUP>5</SUP> and Pr=0.1 at angles of 0° and 45°. However, in the other cases, the flow and heat transfer characteristics are independent of the time.The surfaceaveraged Nusselt number increases with an increase in the Prandtl number. As the Prandtl number increases, the Nusselt number becomes larger regardless of the angle for Ra=10<SUP>5</SUP> . In particular, the Nusselt number steeply increases when the angle is 45° for Ra=10<SUP>5</SUP> and Pr=0.1.
이성진,문기수,박용갑,하만영 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.7
This study numerically examines the flow around a pair of parallel rectangular cylinders placed perpendicular to the direction of the flow using the immersed boundary method at a fixed Reynolds number of 100. A total of eight spacing ratios between 0.1 and 2 are considered in the two arrangements of the cylinders. The two cylinders are arrayed in inline and a staggered arrangement. The pattern of the wake of the two cylinders depends on their arrangements and spacing. The results, show four flow regimes: (i) A single bluff-body regime, (ii) an asymmetric wake regime, (iii) a transition regime, and (iv) a coupled street regime. All flow regimes appear in the case of the inline arrangement. In the case of the staggered arrangement, only the three flow regimes other than the coupled street flow regime are shown. The flow characteristics depend on the flow regime, including the flow structure, drag force, lift force, and frequency. We analyzed the flow characteristics by comparing the flow regimes, vortex shapes, drag and lift coefficients, and Strouhal numbers, which depended on the arrangement. The results of the drag, lift, and Strouhal numbers depend on the interaction of the jet that forms between the cylinders and the adjacent wakes near the cylinder. Therefore, the flow characteristics are sensitive to the arrangement and the distance between the cylinders.
박재현,김민성,문기수,박용갑,하만영 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.7
Two-dimensional numerical simulations were used to analyze the temperature-driven natural convection phenomena in a square enclosure with an inner cylinder in the Rayleigh number range of 5 6 Ra = 10 ~ 10 . The immersed boundary method based on the finite volume method (FVM) was applied to generate and treat inner cylinders, which remained at constant high temperature with no-slip boundary condition. The cylinder remained at a constant high temperature with no-slip boundary conditions. The detailed phenomena of natural convection were investigated according to the bottom wall temperature with a cold and isothermal top walls and adiabatic side walls. The numerical solutions at a Rayleigh number of 5 10 reached steady state once the solutions fully converged. When the Rayleigh number increased to 6 10 , the solution showed unsteady characteristic depending on the bottom wall temperature. In addition, the distribution of the isotherms in the lower part of the enclosure depended on the temperature variation of the bottom wall and the Rayleigh number. These effects had a significant influence on the convection structure in the lower part of the enclosure and on the corresponding heat transfer on the walls. The convection structures in the enclosure changed significantly in several cases at 6 10 with a high bottom wall temperature.