• Journal of Advanced Marine Engineering and Technology
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• v.31 no.2
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• pp.159-165
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• 2007

The Characteristics of the flowfield around two circular cylinders in tandem arrangement was investigated by PIV. Strouhal numbers. velocity vectors and velocity profiles were observed at centre-to-centre space ratios of P/D= 1.5. 2.0 and 2.5, and Reynolds number of $Re=3.0{\times}10^3{\sim}5.0{\times}10^3$. As the results the Strouhal numbers measured in the rear region of the cylinder of wake side were decreased with the space ratios. The flow between two cylinders was almost stagnated and the size of the stagnated region was larger in the close side than in the far side of the front cylinder. The direction of vortex between two cylinders was opposed each other with the small difference(${\alpha}\;{\pm}1.0^{\circ}$) of the attack angle ${\alpha}$.

• Journal of Power System Engineering
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• v.20 no.1
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• pp.69-74
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• 2016

The local heat transfer and pressure drops of developed turbulent flows in the convergent channels with square cross-sectional areas along the streamwise distance have been investigated experimentally. Four different parallel angled ribs (a = $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, and $90^{\circ}$) are placed to the one sided wall only, respectively. The ribbed walls are manufactured with a fixed rib height (e)=10 mm and the ratio of rib spacing (p) to height (e) = 10. The measurement was run within the range of Reynolds numbers from 22,000 to 79,000. The result shows that the increases in the Nusselt numbers for the flow attack angles can be seen in the order of $30^{\circ}$, $45^{\circ}$, $60^{\circ}$ and $90^{\circ}$.

• Korea-Australia Rheology Journal
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• v.16 no.1
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• pp.47-54
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• 2004

Low Reynolds number, dilute, and surfactant-free bubble suspensions are prepared by mechanical mixing after introducing carbon dioxide bubbles into a Newtonian liquid, polyol. The apparent shear viscosity is measured with a wide-gap parallel plate rheometer by imposing a simple shear flow of capillary numbers(Ca) of the order of $10^{-2}$ ~ $10^{-1}$ and for various gas volume fractions ($\phi$). Effects of capillary numbers and gas volume fractions on the viscosity of polyol foam are investigated. At high capillary number, viscosity of the suspension increases as the gas volume fraction increases, while at low capillary number, the viscosity decreases as the gas volume fraction increases. An empirical constitutive equation that is similar to the Frankel and Acrivos equation is proposed by fitting experimental data. A numerical simulation for deformation of a single bubble suspended in a Newtonian fluid is conducted by using a newly developed two-dimensional numerical code using a finite volume method (FVM). Although the bubble is treated by a circular cylinder in the two dimensional analysis, numerical results are in good agreement with experimental results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.71-80
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• 1985

The various sizes of wires are attached to the outside of the inner tube in a double pipe heat exchanger to enhance the thermal performance. The diameters of the wires range from 0.5mm to 1.6mm while the pitches are chosen between 5mm and 50mm. Experiments have been performed with the range of Reynolds numbers from 15000 to 30000 in annular space where air flows. The friction factors are increased by 1.5 to 4.5 times depending on the sizes and the pitches of the wires. However, the Nusselt numbers are increased by the factors of 1.8 to 2.8 within this experimental range. It is suggested that there should be an optimum configuration rendered when the weighting values of the heat transfer promotion and the pumping power are given.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.1
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• pp.94-99
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• 2008

The characteristics of the flowfield of a square prism having fences on the corner was investigated by the PIV. Strouhal numbers, velocity vectors and velocity profiles around the square prism were observed at various positions of the fences, and Reynolds number of $Re=0.6{\times}10^4{\sim}1.0{\times}10^4$. As the results in case of the prism having fences the Strouhal numbers were all smaller than in case of the prototype prism. In case of the prism having vertical fences on the front corners the concentrated intensity of the vorticity was the strongest and the size of separated shear layer was the largest. While in case of the prism having vertical fences on the rear corners the concentrated intensity of the vorticity was the weakest and the size of separated shear layer was the smallest. Also in this case, the flow separated in front corner was reattached around the rear corner and made circulation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.537-544
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• 2005

The present study numerically investigates two-dimensional fluid flow in the confined jet flow in the presence of applied magnetic field. Numerical simulations to calculate the fluid flow and heat transfer in the confined jet are performed for different Reynolds numbers in the absence and presence of magnetic fields in the range of $0{\le}N{\le}0.05$, where N is the Stuart number (interaction parameter) which is the ratio of electromagnetic force to inertia force. The present study reports the detailed information of flow in the channel at different Stuart numbers. As the intensity of applied magnetic fields increases, the vortex shedding formed in the channel becomes weaker and the oscillating amplitude of impinging jet decreases. The flow fields become the steady state if the Stuart number is greater than a critical value. Thus the pressure coefficients at the stagnation point also vary as a function of Stuart number.

• Journal of Mechanical Science and Technology
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• v.18 no.2
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• pp.313-324
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• 2004

A rich phenomenon in the dynamics of azimuthal vortices in a circular cylinder caused by the inertial oscillation is investigated numerically at high Reynolds numbers and moderate Rossby numbers. In the actual spin-up flow where both the Ekman circulation and the bottom friction effects are included, the first appearance of a seed vortex is generated by the Ekman boundary-layer on the bottom wall and the subsequent roll-up near the corner bounded by the side wall. The existence of the small vortex then rapidly propagates toward the inviscid region and induces a complicated pattern in the distribution of azimuthal vorticity, i.e. inertial oscillation. The inertial oscillation however does not deteriorate the classical Ekman-pumping model in the time scale larger than that of the oscillatory motion. Motions of single vortex and a pair of vortices are further investigated under a slip boundary-condition on the solid walls. For the case of single vortex, repeated change of the vorticity sign is observed together with typical propagation of inertial waves. For the case of a pair of vortices with a two-step profile in the initial azimuthal velocity, the vortices' movement toward the outer region is resisted by the crescent-shape vortices surrounding the pair. After touching the border between the core and outer regions, the pair vortices weaken very fast.

• Journal of the Korean Society of Visualization
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• v.6 no.2
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• pp.3-8
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• 2008

A new 3D-PTV algorithm(a Volume PTV) based upon a hybrid fitness function has been constructed. A coherency fitness function is introduced using the information of space and time to sort out the correct particle pairs between the two camera images. The measurement system consists of two-high-definition-cameras($1k{\times}1k$), a Nd-Yag laser and a host computer. The developed algorithm has been employed to investigate the flow features of the cylinder wake. The Reynolds numbers with the cylinder diameter(d=10 mm) are 360, 540, 720, 900, 1080 and 1260. Two-dimensional displacements of the particles of each camera's image and neighbouring constraints were introduced to reduce the calculation loads. More than 10,000 instantaneous 3D vectors have been obtained by the constructed algorithm. The constructed algorithm could recover more than $80{\sim}90%$ of the particle numbers in the image condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.3
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• pp.373-385
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• 1998

The local Nusselt numbers have been measured for a round turbulent jet impinging on the convex surface with and without rib. Liquid crystal/transient method was used to determine the Nusselt number distributions along the surface. The temperature on the surface was measured to within .+-.0.25 deg. C accuracy using liquid crystal and a digital color image processing system. The experiments were made for the jet Reynolds number (Re) 23,000, the dimensionless nozzle-to-surface distance (L/d) from 6 to 10, the dimensionless surface curvature (d/D) 0.056, and the various rib types (height(d$_{1}$) from 1 to 2 mm, pitch (p) from 6 to 32 mm). It was found that the average Nusselt numbers on the convex surface with rib are higher than those without rib, mainly due to an increase in the turbulent intensity caused by flow separation, recirculation and reattachment on the wall surface. In addition, we compared the results by the steady-state method using the gold-film Intrex with those by the transient method.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.5
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• pp.906-919
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• 2015

The Deep Draft Semi-Submersible (DDS) concepts are known for their favourable vertical motion performance. However, the DDS may experience critical Vortex-Induced Motion (VIM) stemming from the fluctuating forces on the columns. In order to investigate the current-induced excitation forces of VIM, an experimental study of flow characteristics around four square-section cylinders in a square configuration is presented. A number of column spacing ratios and array attack angles were considered to investigate the parametric influences. The results comprise flow patterns, drag and lift forces, as well as Strouhal numbers. It is shown that both the drag and lift forces acting on the cylinders are slightly different between the various L/D values, and the fluctuating forces peak at L/D = 4.14. The lift force of downstream cylinders reaches its maximum at around ${\alpha}=15^{\circ}$. Furthermore, the flow around circular-section-cylinder arrays is also discussed in comparison with that of square cylinders.