Yong Gap Park

Natural Convection in a Square Enclosure with Differentially Heated Two Horizontal Cylinders

The present study numerically investigates two-dimensional natural convection in a cooled square enclosure with two inner circular cylinders, which have different isothermal conditions for different Rayleigh numbers in the range of 103 ≤ Ra ≤ 105. The cooled and heated isothermal conditions are imposed on the upper and lower cylinders, respectively. The centers of two equidiameter cylinders are placed at those of the lower and upper half of the enclosure, respectively, and the radius of inner cylinders varies. For all Rayleigh numbers, as the radius increases, the cold upper cylinder occupies a much wider area in the upper half of the cold enclosure, resulting in the formation of a wider dead zone of the heat transfer and fluid flow in the upper half of the enclosure. Regardless of the radius variation, the circulation of the flow shows two overall rotating symmetric eddies with the secondary vortices over the upper surface of the upper cylinder. The trajectories of the primary eddy and secondary vortices considerably depend on the radius, especially at a higher Rayleigh number. The dependence of the Nusselt number on the radius and the Rayleigh number is presented.

Natural Convection in a Square Enclosure with Two Horizontal Cylinders

This study investigates natural convection in a cooled square enclosure with two inner heated circular cylinders with the same diameter. The centers of two equidiameter cylinders are placed at those of the lower and upper half of the enclosure, respectively. The immersed boundary method (IBM) to model the inner circular cylinders based on the finite volume method is used to study a two-dimensional natural convection for different Rayleigh numbers varying in the range of 103 ≤ Ra ≤ 105. The effect of the radius of inner circular cylinders in an enclosure on heat transfer and fluid flow at different Rayleigh numbers has been examined. As the Rayleigh number increases, the horizontal symmetry is broken and the asymmetry occurred from the smaller radius. As the radius decreases, the dependence of the convection on the Rayleigh number is considerable. The dependence of the Nusselt number on the radius and the Rayleigh number is presented.

Response characteristics of vortex around the fixed and freely rotating rectangular cylinder with different width to height ratios

This paper presents a numerical investigation for the response characteristics of vortex around the fixed and freely rotating rectangular cylinder about a fixed axis through its centroid. The direct–forcing/fictitious domain (DF/FD) method is used to realise fluid–structure interaction (FSI) problem. In order to identify the effect of Reynolds number and width to height ratio on the flow characteristics and structure motion by FSI, we consider flow over a rectangular cylinder in the range of 50 ≤ Re ≤ 150 and 0.2 ≤ W/H ≤ 1.0, where Re and W/H are the Reynolds number and the width to height ratio. We also compare the freely rotating cylinder case with the fixed cylinder case. In the freely rotating case, the motion of rectangular cylinder is classified into the two different regimes. In the first regime, the rectangular cylinder exhibits periodic oscillation behaviour. In the second regime, it reveals autorotation. All the cases show the periodic oscillation behaviour except the cases of Re = 100 and 150 with W/H = 1.0 whose motion is autorotation.

Numerical study on the laminar fluid flow characteristics around a rectangular cylinder with different width to height ratios

The present study numerically investigates laminar fluid flow past a rectangular cylinder with different width to height ratios. The mass and momentum conservation equations to govern the fluid flow around the rectangular cylinder are solved using the finite volume method which has the second order accuracy and the immersed boundary method is used to handle effectively the rectangular cylinder. The Reynolds number Re and the width to height ratio W/H are varied in the range of 50 Re 150 and 0.1 W/H 1, respectively. The distribution of the Strouhal number and the drag and lift coefficients strongly depend on the fluid flow and vortex structure around the rectangular cylinder varying as a function of the width to height ratio and the Reynolds number. The Strouhal number decreases monotonically with increasing width to height ratio in the Reynolds number varying in the range of 50 to 80. However, as the width to height ratio increases in the Reynolds number varying in the range of 90 to 150, the Strouhal number increases until it has a maximum value, followed by the decrease in its value.