• The KSFM Journal of Fluid Machinery
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• v.11 no.6
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• pp.46-53
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• 2008

Flow structures in an axial compressor with a non-uniform tip clearance were predicted by solving a simple prediction method. For more reliable prediction at the off-design condition, off-design flow characteristics such as loss and flow blockage were incorporated in the model. The predicted results showed that flow field near the design condition is largely dependent on the local tip clearance effect. However overall flow field characteristics are totally reversed at off-design condition, especially at the high flow coefficient. The tip clearance effect decreases, while the local loss and flow blockage make a complicated effect on the compressor flow field. The resultant fluid induced Alford's force has a negative value near the design condition and it reverses its sign as the flow coefficient increases and shows a very steep increase as the flow coefficient increases.

• 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.

• Korean Chemical Engineering Research
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• v.48 no.4
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• pp.470-474
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• 2010

In this study, we presents a simple microfluidic approach for generating uniform Poly(ethylene glycol)(PEG) microfiber. Elongated flow pattern of monomer induced by sheath flow of immiscible oil as continuous phase is generated in Y-shape junction and in situ polymerization by UV exposure. For uniform microfiber, we investigate the optimized flow condition and draw phase diagram as function of Ca and Qd. At the region for stable elongated flow pattern, the microfiber generated in microfluidic chip is very uniform and highly reproducible. Importantly, the thickness of microfibers can be easily controlled by flow rate of continuous and disperse phase. We also demonstrate the feasibility for biological application as encapsulating FITC-BSA in PEG microfiber.

• Nuclear Engineering and Technology
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• v.29 no.2
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• pp.110-126
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• 1997

A two-dimensional continuum model for the hydrogen mining phenomena in the containment subcompartment under severe accident conditions has been developed to predict the spatial distribution of the hydrogen concentration. The model can predict the distribution of time-dependent hydrogen concentration for HEDL experiments well. For the simulation of these experiments, the hydrogen is mixed uniform within the test compartment. To predict the extent of non-uniform distribution, the dominant factors such as the geometrical shape of obstacle and velocity of source injection in mixing phenomena are investigated. If the obstacle disturbing the flow of gas mixture exists in the compartment, the uniform distribution of hydrogen might be not guaranteed. The convective circulation of gas flow is separately formed up and down of the obstacle position, which makes a difference of hydrogen concentration between the upper and lower region of the compartment. The recirculation flow must have a considerable mass flow rate relative to velocity of the source injection to sustain the well-mixed conditions of hydrogen. Finally, in order to account for non-uniform distribution of the hydrogen due to the geometrical configuration the maximum-to-average ratio is functionalized.

• Journal of computational fluids engineering
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• v.18 no.1
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• pp.7-12
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• 2013

This paper presents a numerical investigation of the influences of various non-uniform tip clearances on the performance and flow field in a centrifugal compressor. Numerical simulations were conducted for three centrifugal compressor impellers in which the tip clearance height varied linearly from the leading edge to the trailing edge. The numerical result was compared with the experimental data for validation. Although the performance improved for low tip clearances, a smaller tip clearance at the trailing edge reduced the overall tip leakage flow more effectively than a smaller tip clearance at the leading edge. Therefore, a smaller tip clearance at the trailing edge lowered the mixing loss caused by interactions between the tip leakage flow and the main passage flow.

• Nuclear Engineering and Technology
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• v.50 no.7
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• pp.1079-1087
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• 2018

There are many parameters that affect the natural circulation flow, such as height difference, heating power size, pipe diameter, system pressure and inlet temperature and so on. In general analysis the heating power is often regarded as a uniform distribution. The ANSYS-CFX numerical analysis software was used to analyze the flow heat transfer of supercritical water under different heating power distribution conditions. The distribution types of uniform, power increasing, power decreasing and sine function are investigated. Through the analysis, it can be concluded that different power distribution has a great influence on the flow of natural circulation if the total power of heating is constant. It was found that the peak flow of supercritical water natural circulation is maximal when the distribution of heating power is monotonically decreasing, minimal when it is monotonically increasing, and moderate at uniform or the sine type of heating. The simulation results further reveal the supercritical water under different heat transfer conditions on its flow characteristics. It can provide certain theory reference and system design for passive residual heat removal system about supercritical water.

• Journal of Korean Society on Water Environment
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• v.25 no.5
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• pp.651-660
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• 2009

Detailed flow analysis in river is essential to increase the accuracy of water quality simulation since flow variation depends on many factors such as cross sections, channel slopes, and bed materials. In the QUAL2E stream water quality simulation model, the hydraulic coefficients are assigned to the reach that is collection of computational element using the hydraulic coefficient. This study developed a module that can incorporate the results of non-uniform flow analysis and assign such information to each individual element. Model application focused on the upstream of the Hoengseong reservoir including the reservoir where significant flow change is expected. Comparing with original QUAL2E model the developed module improved the result of water quality simulation without considering the relation of flow velocity and flow depth in terms of flow rates.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.165-172
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• 1993

On the basis of Nikuradse laboratory experiments conducted in circular pipe with uniform roughness, five flow regimes are defined with respect to the characteristics of boundary layer such as laminar, transition laminar, smooth turbulent, transition turbulent and rough turbulent flows. Two cases are found for the transition laminar flow: one for the transition between laminar flow and smooth turbulent flow and the other for the one between laminar flow and rough turbulent flow. They all can be clearly determined by the relative roughness or the ratio of pipe diameter to the roughness. Explicit functions are developed for the estimation of pipe friction factor for the various flow conditions including turbulent flow regimes, which have excellent agreement with the Nikuradse laboratory data.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.567-570
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• 2010

With continuously increasing flat panel display size, uniformity of thin film deposition has been drawing more attentions and associated fabrication methodologies are being actively investigated. Since the convective flow field of mixture gas plays a significant role for deposition characteristics of thin film in an APCVD system, it is greatly important to maintain uniform distribution and consistent concentration of mixture gas species. In this paper, computational study has been performed for the improvement of flow uniformity of mixture gas in an APCVD reactor during thin film deposition process. A diffuser slit has bee designed to spread the locally concentrated gas flow exiting from the flow distributor. A uniform flow distributor has been developed which has less dependency on operating conditions for global flow uniformity

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.699-702
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• 2002

Shunt valves implanted in the subcutaneous tissue of brain to treat patient with hydrocephalus were numerically simulated to investigate influence of pressure pulsation on their flow control characteristics. Shunt valves are subjected to pressure variation since ventricles enclosing the brain are under pressure pulsation rather than uniform pressure due to blood pressure variation. We modeled flow orifice through shunt valve and imposed pulsating pressure and valve diaphragm movement to compute flow through the valve. The results of our study indicated that flow rate increased by $40{\%}$ by introducing pressure pulsation and diaphragm movement on the shunt valve. Our results demonstrate the pressure-flow control characteristics of shunt valves unplanted above human brain may be quite different from the characteristics obtained by syringe pump test with uniform pressure and no diaphragm movement.