• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.1 s.232
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• pp.139-150
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• 2005

The present study has numerically investigated two-dimensional laminar flow over a circular cylinder with a uniform planar shear, where the free-stream velocity varies linearly across the cylinder. Numerical simulations using the immersed boundary method are performed for the ranges of $50{\le}Re{\le}160,\;K{\le}0.2$, and B=0.1 and 0.05 where Re, K and B are the Reynolds number, the non-dimensionalized velocity gradient and the blockage ratio, respectively. Results show that the flow depends significantly on B as well as Re and K. It is found, especially, that the blockage effect accounts for some causes of apparent discrepancies among previous studies on the flow. With increasing K, the vortex shedding frequency and the mean drag stay nearly constant or slightly decrease whereas the mean lift, acting from the higher-velocity side to the lower, increases linearly. Flow statistics as well as instantaneous flow fields are presented to identify the characteristics of the flow and then to understand the underlying mechanism.

• Membrane Journal
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• v.7 no.3
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• pp.142-149
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• 1997

The extended analysis on the diverging flow through asymmetric membrane pores has been performed in this study. Afore rigorous equations of velocity profile relevant to the divergent slit and cone shaped channels, which are widely used as a general pore model, have been obtained by employing a creeping flow approach of Newtonian fluids. As a degree of asymmetry (i.e., diverging angle) is increased, the predicted flow function shifts Toward the center region due to the incorporated wall effect, so that the overall velocity profile becomes decreased. It is true, as expected, that when the divergent channel is in the low diverging angle limit, the channel flow results in the Poiseuillean fashion by utilizing a lubrication approximation. The flow rate equation of each type of channel has been developed from the combined solution of velocity profile and pressure fields. The effect of diverging flow on the flow rate enhancement has been remarkably predicted, in which the flow rate increases with the increase of pore asymmetry. The advantage of our theoretical results lies in the analytical expression for the diverging flow behavior through pore channels as well as its ability to play a fundamental role on the related membrane filtrations such as microfiltration and ultrafiltration.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.10a
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• pp.213-219
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• 2001

In this paper, particle velocity of slurry flow, a kind of solid-particle two phase flow, was measured by using a particle tracking velocimetry. Particles are modeled by sphere-shaped glass whose diameters are 3mm, 5mm, and 7mm At first, a particle which is falling in the water is captured and analyzed to give their free falling velocity. The falling velocity was very high up to about 4m/sec in the air, which needs special algorithm for the accurate measurement. For the upwelling slurry flow in the straight duct, there are some noises caused by cavity. However, the effect was so small that it does not affect the measurement of large particles. From the preliminary study of applying the PTV to measurement of particle movement in slurry flow, we could find out the optimum value of parameters: threshold value., searching area radius and correlation area size.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.2
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• pp.242-254
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• 2016

This paper is the forth investigation on the evaluation methods of flow characteristics in a steady flow bench. In the previous works, it was concluded that the assumption of the solid rotation might cause serious problems and both of the eccentricity and the velocity profile distort the flow characteristics when using the ISM at 1.75B plane. Also particle image velocimetry (PIV) measurement at this position showed that the real velocity profile was far from the assumption of ISM evaluation. In this paper, the planar velocity profiles were measure from 1.75B to 6.00B position by PIV and the characteristics were examined according to the valve angles and lifts for further investigations about the effect of the position on the velocity profile. The results show that $26^{\circ}$ valve angle is always an unique exceptional case in all aspects. If the valve angle is $21^{\circ}$ and below, the planar velocity profiles according to the lift and the position are similar to each other, however, the tangential velocity curves along with the radial direction have common tendencies up to $16^{\circ}$ angle. Also the well arranged swirl behaviors are generally observed at the position above 3.00B and the velocity contour lines come closer to the concentric circle as the valve lift increases. In addition, the gradient of tangential velocity along with the radial direction from the swirl center becomes stable and constant as the position goes downstream. Concurrently the velocity gradient is larger to the eccentric direction of the center. In the meantime the tangential velocity curves along with the radial direction are irregular and various at 1.75B, however, they become regular and reach higher level as the evaluation position goes downstream. At this time the curves of 4.50B are the best fitted to the ideal one. On the other hand in an exceptional case, $26^{\circ}$, the velocity contours are very complicated over 6mm valve lift regardless the position and the gradient increases to the opposite direction of the eccentric center. Also, 6.00B is a best fitting position in the geometrical cylinder center base. With respect to the swirl center, the distribution range of centers for 1.75B is different to that for the other positions and the eccentricities of this plane are larger regardless the valve angle. After 1.75B, there is no certain tendency in the center position change according to the valve angle and lift. Additionally, the eccentricities are not sufficiently small to neglecting the effect on ISM measurement.

• International Journal of Vascular Biomedical Engineering
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• v.4 no.1
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• pp.1-8
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• 2006

The x-ray PIV method was improved for measuring quantitative velocity fields of real blood flows using a coherent synchrotron x-ray source. Without using any contrast media or seeding particles, this method can visualize flow pattern of blood by enhancing the phase-contrast and interference characteristics of blood cells based on a synchrotron x-ray imaging mechanism. The enhanced x-ray images were achieved by optimizing the sample-to-scintillator distance, the sample thickness, and hematocrit. The quantitative velocity fields of blood flows inside opaque tubes were obtained by applying a 2-frame PIV algorithm to the x-ray images of the blood flows. The measured velocity field data show typical features of blood flows such as the yield stress effect. The non-Newtonian flow characteristics of blood flows were analyzed using the x-ray PIV method and the experimental results were compared with hemodynamic models.

• 순환기질환의공학회:학술대회논문집
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• 2006.04a
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• pp.28-36
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• 2006

The x-ray PIV method was improved for measuring quantitative velocity fields of real blood flows using a coherent synchrotron x-ray source. Without using any contrast media or seeding particles, this method can visualize flow pattern of blood by enhancing the phase-contrast and interference characteristics of blood cells based on a synchrotron x-ray imaging mechanism. The enhanced x-ray images were achieved by optimizing the sample-to-scintillator distance, the sample thickness, and hematocrit. The quantitative velocity fields of blood flows inside opaque tubes were obtained by applying a 2-frame PIV algorithm to the x-ray images of the blood flows. The measured velocity field data show typical features of blood flows such as the yield stress effect. The non-Newtonian flow characteristics of blood flows were analyzed using the x-ray PIV method and the experimental results were compared with hemodynamic models.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.561-567
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• 2005

The effect of triangular multi-tabs attached at the perimeter of jet nozzle on flow structure in the near field was investigated experimentally. A stereoscopic PIV(SPIV) system was employed to measure three orthogonal velocity components of the 3-D turbulent jet. In this study, two different types of sharp-edged jet nozzle having 4, 8 tabs were tested at the Reynolds number of Re=10,000. SPIV measurements were carried out at 5 cross-sectional planes. Six hundred instantaneous velocity fields were measured for each experimental condition and they were ensemble averaged to get spatial distributions of turbulent statistics such as mean velocity and turbulence intensity. Entrainment rate of surrounding fluid into the tabbed jets was estimated using the measured 3-D velocity field data. The strong vortex structure was induced for the jet flow with 4 tabs, increasing entrainment rate.

• The KSFM Journal of Fluid Machinery
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• v.8 no.3 s.30
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• pp.26-32
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• 2005

One of noticeable features in the cross flow fan is that a working fluid passes through impeller blade twice without distinction between the inlet and exit angles. Also, it does produce higher circumferential velocity than other types of blade at the same flow rate in accordance with the application of the forward curved shape. However, a design theory for the cross-flow fall has not yet been formed owing to an eccentric vortex, which is the remarkable characteristics, occurred in a cross-flow fan. Furthermore, the eccentric vortex, which is difficult to control the size and position, is the important cause of performance decrease. In this study, experiments we carried out to estimate the similarity of the cross-flow fan with various scales and rotational velocity changes. Pressure coefficients to flow coefficients with various scales of the cross-flow fan are plotted to the application of the general similarity law of the turbomachinery in the cross-flow fan with Archimedes spiral, which is the important factor having an effect on it.

• The KSFM Journal of Fluid Machinery
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• v.12 no.5
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• pp.33-38
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• 2009

In this study, the effect of flow disturbance such as contraction, expansion pipe and velocity deviation from low velocity of $0.1\;^m/s$ to $2.5\;^m/s$ on the error characteristics of the flowmeter was studied. Flow experiments using flowmeter calibration facility of K-water were undertaken for the cases of ultrasonic flowmeter based on transit-time method and electromagnetic flowmeter. Experimental results are presented that measurement error of expansion pipe are larger than contraction pipe. It is shown that the minimum straight length were required to remain of ${\pm}0.5%$ error for electromagnetic flowmeter and ${\pm}2.0%$ error for ultrasonic flowmeter.

• Journal of the Semiconductor & Display Technology
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• v.11 no.4
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• pp.37-42
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• 2012

Nanoimprint lithography (NIL) has attracted broad interest as a low cost method to define nanometer scale patterns in recent years. A major disadvantage of thermal NIL is the thermal cycle, that is, heating over glass transition temperature and then cooling below it, which requires a significant amount of processing time and limits the throughput. One of the methods to overcome this disadvantage is to improve the cooling performance in NIL process. In this paper, the performance of the cooling system of thermal NIL is numerically investigated by SolidWorks Flow Simulation program. The calculated temperatures of nanoimprint device were verified by the measurements. By using the analysis model, the effects of the change of flow velocity and cooler location on the cooling performance are investigated. For the 6 cases (0.1 m/s, 0.5 m/s, 1 m/s, 3 m/s, 5 m/s, 10 m/s) of flow velocity and for the 6 cases of distances (50 mm, 40 mm, 30 mm, 20 mm, 10 mm, 1 mm) of cooler location, the heat conjugated flow analyses are performed and discussed.