• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.59-60
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• 2006

Some useful flow regime data are obtained from the experiments using the flight producing hyper-gravity(2g) conditions and on ground(1g) with the identical flow conditions. The flow regime data obtained at 1g and 2g conditions are compared with new dimensionless flow regime map using Fr, Bo and We number related with gravity, surface tension and inertia force.

• Journal of computational fluids engineering
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• v.20 no.3
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• pp.54-61
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• 2015

In the present study, a flow solver using a kinetic BGK scheme was developed for the compressible Navier-Stokes equation. The kinetic BGK scheme was used to simulate flow field from the continuum up to the transitional regime, because the kinetic BGK scheme can take into account the statistical properties of the gas particles in a non-equilibrium state. Various numerical simulations were conducted by the present flow solver. The laminar flow around flat plate and the hypersonic flow around hollow cylinder of flare shape in the continuum regime were numerically simulated. The numerical results showed that the flow solver using the kinetic BGK scheme can obtain accurate and robust numerical solutions. Also, the present flow solver was applied to the hypersonic flow problems around circular cylinder in the transitional regime and the results were validated against available numerical results of other researchers. It was found that the kinetic BGK scheme can similarly predict a tendency of the flow variables in the transitional regime.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.8
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• pp.1038-1045
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• 2000

An experimental study was carried out to delineate the flow characteristics in a closed countescurrent two-phase thermo syphon with concentric tubes. This is to be installed in the HANARO research reactor as a part of a Cold Neutron Source(CNS). In the present investigation, experiments ata room temperature with Freon-II3 as a moderator were performed. Results show that, based on the magnitude of pressure fluctuation, the flow regimes could be divided into 4 distinct ones in the ($V_f,\;Q_i$) plane, where $V_f$ represents the volume of the charged liquid and $Q_i$ the heat load: a stable flow regime, an oscillatory flow regime, a restablized flow regime and a dryout flow regime. For $V_f$>2.5l, the flow is stable at low $Q_i$. However, as $Q_i$ increases, the flow becomes oscillatory and finally restablizes As $V_f$ increases, the oscillation amplitude decreases, reaching to the restablized flow region at low $Q_i$, and the liquid level in the moderator cell remains high. In the oscillatory flow regimes, for a fixed VI; the oscillating period of time varies with $Q_i$, having a minimum value at a certain value of $Q_i$. The heat load, where the oscillating period of time is minimum, decreases as $V_f$ increases.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3297-3304
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• 1994

Experimental investigation have been made to study the double-diffusive nature of convection of an initially stratified salt-water solution heated from below in a cylindrical cavity. The objective is to examine the process of mixed-layer formation, the flow phenomena, the heat transfer characteristics, and temperature and concentration distribution according to the changes in the effective Rayleigh number based on the reference height which represents the relation of temperature and concentration gradient. The types of initially formed flow pattern are categorized in three regimes depending on the effective Rayleigh number ; stagnant flow regime, single mixed-layer flow regime and successively formed multiple mixed-layer flow regime. The temperature and concentration profiles are both uniform in each layer due to convective mixing in the layered flow regime, but both linear in stagnant flow regime and single mixed-layer flow regime. At the interface between adjacent layers, the temperature changes smoothly but the concentration changes rapidly. The layers expand by diffusion of concentration through the interface along with its random fluctuation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1731-1740
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• 1995

Experimental investigations have been made to study the double-diffusive nature of convection of an initially stratified salt-water solution due to heating from below in a rotating cylindrical cavity. The objective is to examine the flow phenomena and the heat transfer characteristics according to the changes in temperature gradient, concentration gradient and rotating velocity of cavity. Thermal and solutal boundary conditions at side wall are adiabatic and impermeable, respectively. The top and bottom plate are maintained each at constant temperature and concentration. The cavity is put into a state of solid body rotation. Like the stationary case, the types of initially-formed flow pattern are classified into three regimes depending on the effective Rayleigh number and Taylor number; stagnant flow regime, single mixed-layer flow regime and successively formed multi-mixed layer flow regime. At the same effective Rayleigh number, the number of initially-formed mixed layer and its growth rate decrease as the effect of rotation increases. The temperature and concentration profiles are both uniform in each layer due to convective mixing in the layered-flow regime, but look both liner in stagnant flow regime and single mixed-layer flow regime. At the interface between adjacent layers, the temperature changes smoothly but the concentration changes rapidly.

• Nuclear Engineering and Technology
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• v.54 no.2
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• pp.546-553
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• 2022

Narrow rectangular channels are employed in nuclear research reactors that use plate-type nuclear fuels, high heat-flux compact heat exchangers, and high-performance micro-electronics cooling systems. Two-phase flow in narrow rectangular channels is important, and it needs to be better understood because it is considerably different than that in round tubes. In this study, mechanistic models were developed for the flow regime transition criteria for various flow regimes in co-current air-water two-phase flow for vertical downward flow inside a narrow rectangular channel. The newly developed criteria were compared to a flow regime map of downward air-water two-phase flow inside a narrow rectangular channel with a 2.35-mm gap width under ambient temperature and pressure conditions. Overall, the proposed model showed good agreement with the experimental data.

• Wind and Structures
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• v.11 no.3
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• pp.221-240
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• 2008

The spanwise flow structure around a rigid smooth circular cylinder model in cross-flow has been investigated based on the experimental data obtained from a series of wind tunnel tests. Surface pressures were collected at five spanwise locations along the cylinder over a Reynolds number range of $1.14{\times}15^5$ to $5.85{\times}10^5$, which covered sub-critical, single-bubble and two-bubble regimes in the critical range. Separation angles were deduced from curve fitted to the surface pressure data. In addition, spanwise correlations and power spectra analyses were employed to study the spatial structure of flow. Results at different spanwise locations show that the transition into single-bubble and two-bubble regimes could occur at marginally different Reynolds numbers which expresses the presence of overlap regions in between the single-bubble regime and its former and later regimes. This indicates the existence of three-dimensional flow around the circular cylinder in cross-flow, which is also supported by the observed cell-like surface pressure patterns. Relatively strong spanwise correlation of the flow characteristics is observed before each transition within the critical regime, or formation of first and second separation-bubbles. It is also noted that these organized flow structures might lead to greater overall aerodynamic forces on a circular cylinder in cross-flow within the critical Reynolds number regime.

• Journal of Wetlands Research
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• v.21 no.spc
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• pp.1-8
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• 2019

River works for water utilization have substantially altered the natural flow regime, and it has resulted in deformation of healthy river ecosystems. In Korea, river restoration projects have conducted actively since 1990's. Major purposes of the river restoration are the rehabilitation of modified river channel, improvement of water quality, and creation of aquatic habitats as well as recreational spaces using natural material for river work. However, there have been little interests about the restoration of flow regime which influences to most aspects of river ecosystems. The restoration of natural flow regime has received much attention in preservation of aquatic ecosystems. It should be needed to explore the relationship between flow regime and river ecosystems, and the restoring flow regime is essential. This paper introduce the concept of environmental flow through the interrelation between flow regime and river ecosystem. It provides rolls of flow regime and addresses the method of establishing target flow regime using the RVA(Range of Variability Approach) that suggested by Richter et al.(1997) through analysis of altered flow pattern case of Han river basin.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.4
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• pp.342-349
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• 1988

The characteristics of flow pattern transitions in a horizontal cocurrent gas-liquid flow have been investigated by means of a statistical analysis of instantaneous pressure drop curves at an orifice. The dimensionless intensity of pressure drop fluctuation shows a sudden change during the course of flow transitions, indicating that it may be a good measure to identify the flow regime transitions. The probability density function of the curves feature a unique pattern depending upon the flow regimes and the statistical properties of the PDF also have particular ranges for each flow regime. In conclusion, the statistical analysis of instantaneous pressure drops may be a powerful tool for predicting the flow regime transitions.

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.1
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• pp.1-9
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• 2007

This study concerns the characteristics of helical flow in a concentric and eccentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and 0.2% aqueous of sodium carboxymethyl cellulose (CMC), respectively, when the inner cylinder rotates at the speed of 0-500 rpm. The effect of rotation on the skin friction is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and, then, it gradually approach to zero for the turbulent flow regime.