Earticle

Flow control of flow field is essential to design efficient elements relating to fluid machineries. In this study, flow characteristics of rectangular prism with center gap through-flow at different aspect ratio was investigated to flow control. It was used a FLUENT 6.3 version to study flow field. It was found that the through-flow disturbs the development of vertical velocity component and decreased the vortex size and critical value of a rapid change in pressure coefficient distribution.

In this study, a computational work to investigate the influence of a turbulent wake flow by a rectangular prism with different aspect ratio, which is installed at the inlet of a diffuser. The k-ω model was adopted to simulate the turbulence. The continuity and time averaged Navier-stokes equations were solved by a implicit finite volume scheme. The computational results are qualitatively well compared to existing experimental data by PIV. The results show that the velocity recovery of the subsonic diffuser is dependent on the aspect ratio of rectangular prism.

In this study, we have modeled a subsonic diffuser with rectangular prism and tried to investigate the influence of a turbulent wake flow by numerical simulation using computational fluid dynamics based on steady-state Navier-Stokes equation and standard k-ε model. A commercial CFD program, FLUENT, is used on the analysis. The turbulent wake is generated by a rectangular prism, which is installed at the diffuser. Flow Uniformity Showed the best results in the case of AR=1:1 and tended to be uniform in the critical point at Re=8.8×103.

In this study, we have modeled a wide angle diffuser with rectangular prism and tried to investigate the influence of a turbulent wake flow by PIV and a numerical simulation using computational fluid dynamics based on steady-state Navier-Stokes equation and standard k-ε model. A commercial CFD program, FLUENT, is used on the analysis. The turbulent wake is generated by a rectangular prism, which is installed at the diffuser. The results show that it is possible to flow control by installing a rectangular prism within the diffuser and velocity recovery is the highest in aspect ratio 1:1.

In this study, a experimental work to investigate the influence of a turbulent wake flow on the velocity distribution of a diffuser with PIV method. The turbulent wake is generated by a rectangular prism, which is installed at the inlet of a diffuser. The results show that the velocity recovery of the subsonic diffuser is dependent on the height and location of rectangular prism. It is found that a certain height of the rectangular prism to generate the turbulent wake give a better velocity recovery, compared with no rectangular prism.

본 연구는 사면체에서 정의된 내접 장축 회전 타원체를 확장하여 Rectangular Prism의 내접 장축 회전 타원체에 대해 탐구하였다. 또한 평면에서의 삼각형 및 사각형에서 정의되는 슈타이너 내접 타원을 3차원으로 확장하여 Rectangular Prism의 슈타이너 내접 장축 회전 타원체에 대해 탐구하였다. 본 연구를 통해 다음과 같은 결과를 얻을 수 있었다. 첫 번째, Rectangular Prism의 내접 장축 회전 타원체의 두 초점의 위치 관계에 대해 밝혔다. 두 번째, Rectangular Prism의 내접 장축 회전 타원체의 존재성 및 개수에 대해 밝혔다. 세 번째, Rectangular Prism의 슈타이너 내접 장축 회전 타원체의 두 초점의 위치를 밝혔다. 네 번째, Rectangular Prism의 슈타이너 내접 장축 회전 타원체가 존재할 필요충분조건을 발견하였다. 다섯 번째, Rectangular Prism과 Rectangular Prism의 슈타이너 내접 장축 회전 타원체의 부피비를 밝혔다. 본 연구와 같이 기존의 수학 개념을 다른 영역으로 확장하고 평면에서의 결과를 입체에 적용시키는 활동은 수학의 발전에 기여할 것이라 기대한다.

This study extends the concept of the inscribed Prolate Spheroid defined of tetrahedron to explore the inscribed Prolate Spheroid of Rectangular prism. Furthermore, it extends the concept of the Steiner inellipse, defined in triangles andquadrilaterals on a plane, to three dimensions to explore the Steiner inscribed Prolate Spheroid of Rectangular prism. Through this study, the following results were obtained. First, the positional relationship of the two foci of the inscribedProlate Spheroid of Rectangular prism was elucidated. Second, the existence and number of inscribed Prolate Spheroid of Rectangular prism were determined. Third, the positions of the two foci of the Steiner inscribed Prolate Spheroid ofRectangular prism were clarified. Fourth, the necessary and sufficient conditions for the existence of the Steiner inscribed Prolate Spheroid of Rectangular prism were discovered. Fifth, the volume ratio between the Rectangular prism and its Steiner inscribed Prolate Spheroid were revealed. Activities like this study, which extend existing mathematical concepts to other domains and apply planar results to three-dimensional figures, are expected to contribute to the advancement of mathematics.

Effect of boundary layer thickness on the flow characteristics around a rectangular prism has been investigated by using a PIV(Particle Image Velocimetry) technique. Three different boundary layers(thick, medium and thin)were generated in the Atmospheric Boundary Layer Wind Tunnel at Pusan National University. The thick boundary layer having 670mm thickness was generated by using spires and roughness elements. The medium thickness of boundary layer$(\delta=270mm)$ was the natural turbulent boundary layer at the test section with fully long developing length(18m). The thin boundary layer with 36.5mm thickness was generated by on a smooth panel elevated 70cm from the wind tunnel floor. The Reynolds number based on the free stream velocity and the height of the model was $7.9{\times}10^3$. The mean velocity vector fields and turbulent kinetic energy distribution were measured and compared. The effect of boundary layer thickness is clearly observed not only in the length of separation bubble but also in the reattachment points. The thinner boundary layer thickness, the higher turbulent kinetic energy peak around the model roof. It is strongly recommended that the height ratio between model and approaching boundary layer thickness should be a major parameter.

직육면체 프리즘에 대한 중력, 자력, 중력 변화율 텐서 및 자력 변화율 텐서 반응식을 정리하였다. 직교 좌표계에서 직육면체 프리즘에 대한 삼중 적분으로 수직 중력을 유도하고, 직육면체의 축 방향 대칭성을 이용하여 순환 치환으로 두 개의 수평 중력 성분을 유도한다. 벡터 중력을 각 성분 별로 미분하여 중력 변화율 텐서를 유도한다. 포아송(Poisson) 관계식을 이용하면 일정한 방향으로 자화된 벡터 자력은 중력 변화율 텐서로부터 얻어진다. 벡터 자력을 각 방향으로 미분하여 최종적으로 자력 변화율 텐서를 유도하였다.

The closed-form expressions of gravity, magnetic, gravity gradient tensor, and magnetic gradient tensor due to a rectangular prism are derived. The vertical gravity is derived via triple integration of a rectangular prism in Cartesian coordinates, and the two horizontal components of vector gravity are then derived via cycle permutation of the axis variables of vertical gravity through the axial symmetry of the rectangular prism. The gravity gradient tensor is obtained by differentiating the vector gravity with respect to each coordinate. Using Poisson's relation, a vector magnetic field with constant magnetic direction can be obtained from the gravity gradient tensor. Finally, the magnetic gradient tensor is derived by differentiating the vector magnetic with respect to appropriate coordinates.