• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.689-696
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• 1996

A comparison is made of the heat loss from a hollow cylinder, computed using an one-dimensional analytic method and a two-dimensional separation of variables scheme. For a two-dimensional analysis, the temperature of the inner surface as a boundary condition can be varied along the length of the cylinder by varing the temperature variation factor, b. Comparisons of the heat loss from the hollow cylinder using these two methods are given as a function of non-dimensional cylinder length, the ratio of the outer radius to the inner radius, temperature variation factor and Biot number. The result shows that the value of the heat loss from the hollow cylinder obtained using the one-dimensional analytic method becomes close to the value given by the two-dimensional separation of variables scheme as the value of Biot number and the non-dimensional hollow cylinder length increase and as the ratio of the outer radius to the inner radius decreases.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.980-985
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• 2003

The present study addresses a computational work to investigate the influence of a turbulent wake flow on the pressure recovery of a subsonic diffuser. The turbulent wake is generated by a cylinder with a small diameter, which is installed at the inlet of a 2-dimensional diffuser. Computation are applied to three-dimensional steady Navier-Stokes equations. The fully implicit finite volume scheme is used to discretize the governing equations. The computational results are qualitatively well compared to the experimental results. The results show that the pressure recovery of the subsonic diffuser is dependent on the diameter and location of cylinder. It is found that a certain diameter and location of the cylinder to generate the turbulent wake give a better pressure recovery, compared with no cylinder flow.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.247-252
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• 2001

The flow around free end of a finite circular cylinder(FC) embedded in an atmospheric boundary layer has been investigated experimentally. The experiments were carried out in a closed-return type subsonic wind tunnel with varying aspect ratio of the finite cylinder mounted vertically on a flat plate. The wake structures behind a 2-D cylinder and a finite cylinder located in a uniform flow were also measured for comparison. Reynolds number based on the cylinder diameter was about Re=20,000. A hot-wire anemometer was employed to measure the wake velocity and the mean pressure distributions on the cylinder surface were also measured. The flow past the FC free end shows a complicated three-dimensional wake structure and flow phenomenon is quite different from that of 2-D cylinder. The three-dimensional flow structure was attributed to the downwashing counter rotating vortices separated from the FC free end. As the FC aspect ratio decreases, the vortex shedding frequency is decreased and the vortex formation length is increased compared to that of 2-D cylinder. Due to the descending counter-rotating twin-vortex, in the region near the FC free end, regular vortex shedding from the cylinder is suppressed and the vortex formation region is hardly established. In the wake center region, the mean velocity for the FC located in atmospheric boundary layer has large velocity deficit, compared to that of uniform flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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• pp.495-505
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• 2009

A two-dimensional circular cylinder freely falling in a channel has been simulated by using immersed boundary - lattice Boltzmann method (IB-LBM) in order to analyze the characteristics of motion originated by the interaction between the fluid flow and the cylinder. The wide range of the solid/fluid density ratio has been considered to identify the effect of the solid/fluid density ratio on the motion characteristics such as the falling time, the transverse force and the trajectory in the streamwise and transverse directions. In addition, the effect of the gap between the cylinder and the wall on the motion of a two-dimensional freely falling circular cylinder has been revealed by taking into account a various range of the gap size. As the cylinder is close to the wall at the initial dropping position, vortex shedding in the wake occurs early since the shear flow formed in the spacing between the cylinder and the wall drives flow instabilities from the initial stage of freely falling. In order to consider the characteristics of transverse motion of the cylinder in the initial stage of freely falling, quantitative information about the cylinder motion variables such as the transverse force, trajectory and settling time has been investigate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.285-293
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• 1997

Numerical calculations has been performed for the flow and heat transfer to a circular cylinder from a hot circular impinging air jet. The characteristics of the flow and heat transfer are investigated and compared with the two-dimensional flow. The present study lays emphasis on the investigation on the flow and heat transfer of the three-dimensionality. The effects of the buoyancy force and the size of jet are also studied. The noticeable difference between the three and the two-dimensional cases is that there is axial flow of low temperature into the center-plane of the cylinder from the outside in the recirculation region. Local Nusselt number over the cylinder surface has higher value for the large jet as compared with that of the small jet since the energy loss of hot jet to the ambient air decreases with increase of the jet size. As buoyancy force increases the flow accelerates so that the period of cooling by the ambient air is reduced, which results in higher local Nusselt number over the surface.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1720-1725
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• 2004

The present study addresses a computational work to investigate the influence of a turbulent wake flow on the pressure recovery of a two-dimensional subsonic diffuser. The turbulent wake is generated by a cylinder with a small diameter, which is installed at the diffuser inlet. Computation is applied to two-dimensional steady Navier-Stokes equations. The computational results are qualitatively well compared to existing experimental data. The results show that the diffuser pressure recovery is strongly dependent on the diameter and location of the cylinder. It is found that there is a certain diameter and location of cylinder for the diffuser pressure recovery to be most enhanced. Compared with no cylinder case, the diffuser performance increases up 24%.

• Bulletin of the Society of Naval Architects of Korea
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• v.23 no.2
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• pp.21-26
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• 1986

An analysis is made of hydrodynamic forces acting horizontally on a two-dimensional cylinder, when it is exposed to incident waves and consequently undergoes a swaying motion in shallow water. Applying the method of matched asymptotic expansions the added mass, wave damping and the wave exciting force are obtained in terms of the difference in potential across the cylinder in a simple manner. The potential jump is related to the so-called blockage coefficient which is determined purely from geometry. It is found that the wave damping coefficient can not exceed the blockage coefficient.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.10
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• pp.895-900
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• 2013

A two-dimensional Stokes flow past a circular cylinder in a channel is analyzed. The circular cylinder is located at the center of the channel, and a plane Poiseuille flow exists upstream and downstream far from the circular cylinder. The Stokes approximation is used, and the flow is investigated analytically by using the eigenfunction expansion and the least square methods. From the analysis, the stream function and pressure distribution are obtained, and the pressure and shear stress distributions on the circular cylinder and channel wall are calculated. The additional pressure drop induced by the circular cylinder and the force exerted on it are calculated as functions of the length of the radius of the circular cylinder. For a typical length of the radius of the circular cylinder, the streamline pattern and pressure distribution are shown.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2489-2494
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• 2008

The two-dimensional circular cylinder freely falling in a channel has been simulated by using Immersed boundary - lattice Boltzmann method in order to analyze the characteristics of motion originated by the interaction between the fluid and the solid. The wide range of the solid/fluid density ratio has been considered to identify the effect of the solid/fluid density ratio on the motion characteristics such as the falling time, the terminal velocity and the trajectory in the vertical and horizontal directions. In addition, the effect of the gap between the cylinder and the wall on the motion of two-dimensional circular cylinder freely falling has been revealed by taking into account a various range of the gap size. The Reynolds number in terms of the terminal velocity is diminished as the cylinder becomes close to the wall at the initial dropping position, since the repulsive force induced between the cylinder and wall constrains the vertical motion. Quantitative information about the flow variables such as the pressure coefficient and vorticity on the cylinders is highlighted.

• Journal of Advanced Marine Engineering and Technology
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• v.14 no.1
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• pp.62-71
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• 1990

Two-dimensional turbulent wake flow past a rectangular cylinder is investigated experimentally by using the linearized constant temperature hot-wire anemometer. Some of turbulent characteristics are obtained at the range of X=6B-500B downstream from the cylinder and the Reynolds number range is 500-2800. For the statistical treatment, autocorrelation coefficient, probability density function and power spectral density function are obtained by using the signal analyzer. It is clear that coherent structure of strong periodic eddies exists to the position of 20B downstream from the cylinder, and its feature is similar to round type as nearer to the cylinder while it is stretched longitudinally along with flow direction as the distance from the cylinder is increased to downstream.