• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.319-322
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• 2006

The flow characteristics around a floating cylinder in a swirling flow field in a vertical pipe with a length of 600mm and an inner diameter of 100mm is investigated by the use of the Stereoscopic-PIV system. The measurement system consists of two cameras, a Nd-Yag laser and a host computer. Optical sensors(LEDs) were used to detect the location of the floating cylinder and to activate the Stereoscopic-PIV system. A conditional sampling Stereoscopic-PIV system was developed in which the flow fields around the floating cylinder are measured at the events of the activations. It has been verified that the motion of the floating cylinder becomes stable when the azimuthal velocity component of the swirl flow is maintained at stable states.

• Wind and Structures
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• v.19 no.4
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• pp.389-404
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• 2014

The flow characteristics of a circular cylinder surrounded by an outer permeable cylinder were experimentally investigated using Particle Image Velocimetry Technique in deep water flow. In order to consider the effects of diameter and porosity of the outer cylinder on flow structures of the inner cylinder, five different outer cylinder diameters (D=37.5, 52.5, 60, 75 and 90 mm) and eight different porosities (${\beta}$=0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85) were selected. During the experiments, the diameter of inner cylinder was kept constant as d=30 mm. The depth-averaged free-stream velocity was adjusted as U=0.156 m/s, which corresponds to the Reynolds number of Re=5000 based on the inner cylinder diameter. It has been concluded that both the outer permeable cylinder diameter and the porosity have important influences on the attenuation of vortex shedding in the wake region. The presence of outer permeable cylinder decreases the magnitude of Reynolds shear stress and turbulent kinetic energy compared to the bare cylinder case. Moreover, the spectral analysis of vortex shedding frequency has revealed that the dominant frequency of vortex shedding downstream of the cylinder arrangement also reduces substantially due to the weakened Karman shear layer instability.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.5
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• pp.121-128
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• 2000

Simple design methods were developed to control the coolant flow rates through cylinder head gasket holes. Applying the concept of flow through an obstruction the ratio of intake to exhaust side flow rates could be easily controlled while maintaining the flow rates per cylinder of the original model. Flow distribution in the coolant passage of the original model was calculated by CFD and the flow rates at the gasket holes were modified based on the calculation results. The calculated flow rated of the modified gasket holes were reasonably close to target values. For more accurate control of the flow rate distribution, a design method with iterative CFD calculations was also suggested. The final size of gasket holes for the target flow rates were obtained just after a few optimization iterations. These methods can be very useful for the optimization of heat transfer characteristics in engine cylinder head and block.

• Wind and Structures
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• v.34 no.1
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• pp.91-100
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• 2022

Numerical simulations are conducted to investigate the uniform flow (UF) and sinusoidal streamwise flow (SSF) over an oscillating 5:1 rectangular cylinder with harmonic heaving motion at initial angles of attack of α = 0° and 3° using two-dimensional, unsteady Reynolds-averaged Navier-Stokes (URANS) equations. First, the aerodynamic parameters of a stationary 5:1 rectangular cylinder in UF are compared with the previous experimental and numerical data to validate the capability of the computationally efficient two-dimensional URANS simulations. Then, the unsteady flow field and aerodynamic forces of the oscillating 5:1 rectangular cylinder in SSF are analysed and compared with those in UF to explore the effect of SSF on the rectangular cylinder. Results show that the alternative vortex shedding is disturbed by SSF both at α = 0° and 3°, resulting in a considerable decrease in the vortex-induced force, whereas the unsteady lift component induced by cylinder motion remains almost unchanged in the SSF comparing with that in UF. Notably, the strong buffeting forces are observed at α = 3° and the energy associated with unsteady lift is primarily because of the oscillations of SSF. In addition, the components of unsteady lift induced by the coupling effects of SSF and cylinder motion are discussed in detail.

• Journal of Mechanical Science and Technology
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• v.19 no.12
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• pp.2270-2280
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• 2005

An experimental study is performed for turbulent swirling flow behind a circular cylinder using 2-D PIV technique. The Reynolds number investigated are 10,000, 15,000, 20,000 and 25,000. The mean velocity vector, time mean axial velocity, turbulence intensity, kinetic energy and Reynolds shear stress behind the cylinder are measured before and behind the round cylinder along the test tube. A comparison is included with non swirl flow behind a circular and square cylinder. The recirculation zones are showed asymmetric profiles.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.704-715
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• 2005

In this study, to investigate in-cylinder tumble or swirl intake flow of a gasoline engine, the flow characteristics were examined with opening control valve (OCV) and several swirl control valves (SCV) which intensify intake flow through steady flow experiment, and also turbulent characteristics of in-cylinder flow field were investigated by 2-frame cross-correlation particle image velocimetry (PIV) method. In the investigation of intake turbulent characteristics using PIV method, the different flow characteristics were showed according to OCV or SCV figures. The OCV or SCV installed engine had higher vorticity and turbulent kinetic energy than a baseline engine, especially around the wall and lower part of the cylinder. Above all, SCV B type was superior to the others. About energy dissipation and reynolds shear stress distribution, a baseline engine had larger loss than OCV or SCV installed one because flow impinged on the cylinder wall. It should be concluded, from what has been said above, as swirl component was added to existing tumble flow adequately, it was confirmed that turbulent intensity was enlarged, flow energy was conserved effectively through the experiment. In other words, there is a suggestion that flow characteristics as these affected to in-cylinder combustion positively.

• International Journal of Automotive Technology
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• v.6 no.5
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• pp.453-460
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• 2005

The tumble or swirl flow is used to promote mixing of air and fuel in the cylinder and to enlarge turbulent intensity in the end of the compression stroke. Since the in-cylinder flow is a kind of transient state with rapid flow variation, which is non-steady state flow, the tumble or swirl flow has not been analyzed sufficiently whether they are applicable to combustion theoretically. In the investigation of intake turbulent characteristics using PIV method, typical flow characteristics were figured out by SCV configurations. An engine installed SCV had higher vorticity and turbulent strength by fluctuation and turbulent kinetic energy than a baseline engine, especially near the cylinder wall and lower part of the cylinder. Above all, the engine with SCV 8 was superior to the others in aspect of vorticity and turbulent strength. For energy dissipation, a baseline engine had much higher energy loss than the engine installed SCV because flow impinged on the cylinder wall. Consequently, as swirl flow was added to existing tumble flow, it was found that fluctuation increased and flow energy was conserved effectively through the experiment.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.115-119
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• 2007

In this paper, a flow visualization analysis has been carried out on an oscillating square section cylinder, numerically, using a commercially available code CFD-ACE. In this study, the square cylinder is forced to oscillate at different frequencies of excitation, viz., fe/fo=0.5, 1.0 and 2.0 (where, fe is the excitation frequency provided to the cylinder and fo is the natural vortex shedding frequency from the stationary cylinder at a particular Reynolds number (=5200). In all the cases, the peak-to-peak amplitude of oscillation is kept at 32% of the side dimension of the square cylinder. These studies are conducted to understand the influence of frequency of oscillation on the flow field features around the cylinder, particularly the mode of vortex shedding. Results indicate that, the flow field around a square cylinder is very much influenced by the excitation frequency, in particular the vortex shedding mode. It is also found that, the vortex street parameters are significantly influence by the oscillation frequency. Comparison with earlier reported experimental studies has also been attempted in this paper. In appears that, such a numerical exercise (as performed in this paper) is first of its kind. It is believed that, these studies would enable one to understand the mechanisms underlying the flow-induced vibrations of a square section cylinder.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.259-264
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• 2001

High-resolution simulations using vortex methods have been performed for simulating unsteady viscous flows around an impulsively started square cylinder. In order to investigate the phenomenon from laminar to transition flow, simulations are performed for Reynolds numbers 25, 50, 150 and 250. At extremely low Reynolds number, flow around a square cylinder is known to separate at the trailing edges rather than the leading edges. With an increase of Reynolds number, the flow separation at the leading edges will be developed. The main flow characteristics of developing recirculation region and separations from leading and trailing edges are studied with the unsteady behavior of the wake after the cylinder starts impulsively. A notable change in the flow evolution is found at Re=150, that is, it is shown that the flow separations begin at both leading and trailing edges of the square cylinder. On the other hand, when Re=250, the strong secondary vorticity from the rear surfaces of the square cylinder increases the drag coefficient as the primary vortex layer is pushed outwards. The comparisons between results of the present study and experimental data show a good consistency.

• Journal of ILASS-Korea
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• v.11 no.1
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• pp.39-47
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• 2006

In-cylinder flows in a motored 3.5L four-valve SI engine were investigated quantitatively using three-component LDV system, to determine how engine configuration affects the flow field. The purpose of this work was to develop quantitative methods which correlate in-cylinder flows to engine performance. For this study, two distinct intake/piston arrangements were used to examine the flow characteristics. Quantification of the flow field was done by calculating two major parameters which are believed to characterize adequately in-cylinder motion. These quantities were turbulent kinetic energy(TKE) and tumble ratio in each plane at each crank angle. The results showed that in-cylinder flow pattern is dominated by the intake effects and two counter rotating vortices, developed during the intake stroke, produced relatively low tumble ratio. Therefore, the applicability of these quantities should be carefully considered when evaluating characteristics resulting from the complex in-cylinder flow motions.