Changyoung Choi

Numerical Simulation of Continuous Casting Process of Different Steel Grades Considering Solidification and Mixing of Different Steel Grades

The continuous casting process of different steel grades is the casting process used to produce different grades of steel without stopping the operation. In this study, an analysis model for which a solidification phenomenon, mixing phenomenon and turbulence taking place inside the mold and the bloom in a continuous casting process of different steel grades were all considered was developed. Based on the comparison between the analysis results of the analysis models for implementation of each phenomenon, an analysis model suitable for analysis of the phenomenon taking place in a continuous casting process of different steel grades was selected. A three-dimensional analysis model was completed by combining the selected optimum analysis methods, and its accuracy was verified by comparing the present numerical result with the result of the experiment. The result of the numerical analysis conducted using the selected model showed that mixing the different grades of steel was promoted and the mixing length was increased by the three-dimensional characteristics of the flow generated inside the mold. The mixing length in the bloom was predicted after the two grades of steel were mixed completely.

Bifurcation of laminar flow around an elliptic cylinder at incidence for low Reynolds numbers

In this study, the fluid flow around an elliptic cylinder inclined to the free-stream was investigated for Reynolds numbers ranging from 20 to 100. The direct-forcing/fictitious domain (DF/FD) method was used to simulate the flow around the elliptic cylinder whose aspect ratio was 0.2 at angles of incidence ranging from 0° to 90°. The resultant instantaneous flow fields and patterns were then compared with those available in existing literature, and it was found that they compared favourably. The transition from steady to unsteady flow was shown using a stability diagram. An increase in the angle of incidence contributed to a decrease in the critical Reynolds number at which the flow became unsteady. In general, as the angle of incidence increased, the value of the Strouhal number decreased for a given Reynolds number. We also constructed a bifurcation diagram in order to distinguish the existence of recirculation regions behind the elliptic cylinder. Various characteristics of flow, such as Strouhal number, stagnation point, and drag and lift coefficients as a function of the angle of incidence were investigated.

Natural Convection in Tilted Square Enclosure with Inner Circular Cylinder at Different Vertical Locations

A numerical analysis of the effect of the position of a circular cylinder in a tilted enclosure on natural convection in the enclosure is presented. The location of the cylinder is changed between -0.4 and 0.4. The Rayleigh number is varied between and . The effect of the location of the cylinder on natural convection in the enclosure is analyzed by the isothermal line, stream line, and surface-averaged Nusselt number. The flow and heat transfer characteristics are independent of time in the range of the Rayleigh number and cylinder location that is considered in this study. The surface-averaged Nusselt number of the cylinder and enclosure increases as the cylinder gets closer to the wall of the enclosure.

Characteristics of Rayleigh–Bénard Convection in a Rectangular Channel With an Inner Hot Circular Cylinder

The immersed boundary method (IBM) was used for three-dimensional numerical simulations, and the results for natural convection in a rectangular channel with an inner hot circular cylinder are presented. This simulation used Rayleigh numbers spanning 3 orders of magnitude, from 1×103 to 1×106. The Prandtl number considered in this study was 0.7. We investigated the effects of the inner cylinders radius on the thermal convection and heat transfer in the space between the cylinder and rectangular channel. A map of the thermal and flow regimes is presented as a function of the cylinders radius and the Rayleigh number.

The Effect of the Prandtl Number on Natural Convection in a Square Enclosure with Inner Cylinder of Various Positions

This paper presents a numerical study conducted for analyzing the effect of the Prandtl number on natural convection in a square enclosure with an inner circular cylinder in various positons. Several Prandtl numbers (Pr = 0.1, 0.7, and 7) and Rayleigh numbers (Ra = 10, 10 and 10) are considered in the numerical study, along with different positions of the inner circular cylinder . The position of the inner circular cylinder is changed in steps of 0.1 in the range of -0.2 to 0.2 . The effect of the Prandtl number on natural convection in the enclosure is analyzed on the basis of the thermal and flow fields and the distribution of the Nusselt number. Regardless of the position of the cylinder, when the Rayleigh number is 10, the surface-averaged Nusselt number of the inner cylinder and the enclosure increases as the Prandtl number increases. § 이 논문은 2014년도 대한기계학회 열공학부문 춘계학술 대회(2014. 4. 23.-26., 제주대) 발표논문임 † Corresponding Author, myha@pnu.ac.kr C 2014 The Korean Society of Mechanical Engineers 성선유 · 최창영 · 하만영 · 윤현식 944

Effect of Prandtl Number on Natural Convection in Tilted Square Enclosure with Inner Circular Cylinder

: 강제 모멘텀 g : 중력가속도 h : 열 소스 및 싱크 k : 열전도 계수 L : 밀폐계 벽면 길이 Key Words: Natural Convection(자연대류), Prandtl Number Effect(Pr 수 영향), Tilted Square Enclosure(기울어진 사각 밀폐계), Inner Circular Cylinder(내부 원형 실린더) 초록: 본 연구에서는 내부에 고온의 원형 실린더가 위치한 저온의 기울어진 사각 밀폐계에서 Prandtl 수 변화에 따른 3밀폐계 4내부 5자연대류 현상에 대한 수치해석을 수행하였다. Rayleigh 수가 10, 10, 10 그리고 밀폐계의 각도가 0°, 15°, 30°, 45° 인 경우에 대해서 Prandtl 수를 0.1, 0.7, 7로 변화시키며 Prandtl 수의 영향을 분석하였다. Prandtl 수의 변화에 따른 밀폐계 내부의 자연대류 현상은 실린더 표면과 밀폐계 벽면의 평균Nusselt 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 10

Flow structure around a square cylinder impacting a wall

The behavior of the flow resulting from the collision of a square cylinder with a wall without rebound at a Reynolds number of 200 was investigated computationally using the direct-forcing/fictitious domain method coupled with the finite volume method. While the emphasis of the numerical simulation was on the case in which the square cylinder collided with the wall at different impact angles, the flow generated by the impact of a circular cylinder was included for comparison. At a Reynolds number of 200, we could not observe any three-dimensional effects in the fluid flow around the square and circular cylinders resulting from the impact regardless of cylinder shape. However, the flow structure around a square cylinder after impact was more complex than that around a circular cylinder. The movement of vortex tubes around each cylinder after impact was influenced not only by the cylinder shape but also by the impact angle. The x- and y-direction drag forces on the cylinder also varied with respect to the cylinder shape and impact angle.