• 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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.10
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• pp.833-843
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• 2002

The present experimental and numerical investigations are performed for the characteristics of transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin- friction coefficients have been measured for the fully developed flow of water and glycerine-water solution (44%) with the inner cylinder rotating at speed of 0∼600 nm, respectively. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.45-50
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• 2001

This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully developed flow of a 0.2 % aqueous solution of sodium carbomethyl cellulose (CMC) at a inner cylinder rotational speed of $0{\sim}600$ rpm. The transitional flow has been examined by the measurement of pressure losses, to reveal the relation of the Reynolds numbers with the skin-friction coefficients, in the laminar and transitional flow regimes. The occurrence of transition has been checked by the gradient change of pressure losses and skin-friction coefficient with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime. Consequently, the critical(axial-flow) Reynolds number decrease as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the onset of taylor vortices.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.631-636
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• 2000

The experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ration of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow have been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.324-329
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• 2001

This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully developed flow of $0.1\sim0.4%$ aqueous solution of sodium carbomethyl cellulose (CMC), respectively at inner cylinder rotational speed of $0\sim600rpm$. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficients due to the rotation in uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical(axial-flow) Reynolds number decrease as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the onset of taylor vortices.

• Journal of Energy Engineering
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• v.11 no.4
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• pp.299-305
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• 2002

The present experimental and numerical investigations are performed on the characteristics of transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully devel-oped flow of water and that of 0.2％ CMC-water solution at a inner cylinder rotational speed of 0∼600 rpm, respectively. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually decreased for turbulent flow regime.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.6
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• pp.822-833
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• 2000

This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow has been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

• Journal of Mechanical Science and Technology
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• v.17 no.4
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• pp.562-570
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• 2003

This experimental study concerns the characteristics of vortex flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and of 0.4% aqueous solution of sodium carboxymethyl cellulose (CMC), respectively, when the inner cylinder rotates at the speed of 0～600 rpm. Also, the visualization of vortex flows has been performed to observe the unstable waves. The results of present study reveal the relation of the bulk flow Reynolds number Re and Rossby number Ro with respect to the skin friction coefficients. In somehow, they show the existence of flow instability mechanism. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. 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. Consequently, the critical (bulk flow) Reynolds number Re$\_$c/ decreases as the rotational speed increases. Thus, the rotation of the inner cylinder promotes the onset of transition due to the excitation of Taylor vortices.

• Journal of the Economic Geographical Society of Korea
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• v.17 no.3
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• pp.567-584
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• 2014

This paper attempts to analyze labor politics under the Kim Young-Sam regime. The labor politics transformed from conflictual pluralism to social partnership. The transition was triggered by the 'IMF economic crisis,' and the transitional direction was determined by the character of political regime and the pattern of social coalitions. These findings imply that the transitional direction of labor politics is not determined by an economic crisis or international pressure, but by the relational dynamics of social coalitions forcing social actors to new perception and strategic choice.

• Nuclear Engineering and Technology
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• v.55 no.11
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• pp.3973-3982
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• 2023

As for two-phase flow in rectangular channels, the flow regimes especially like churn-turbulent and annular flow are significant for the physical problem like Countercurrent Flow Limitation (CCFL). In this study, the rectangular channels with cross-sections of 4 × 66 mm, 6 × 66 mm, 8 × 66 mm are adopted to investigate the flow regimes of air-water vertical upward two phase flow under adiabatic condition. The gas and liquid superficial velocities are 0 ≤ j_g ≤ 20m/s and 0.25 ≤ j_f ≤ 3m/s respectively which covering bubbly to annular flow. The flow regimes are identified by random forest algorithm and the flow regime maps are obtained. As the results, the transitional void fraction from slug to churn turbulent flow fluctuate from 0.47 to 0.58 which is significantly affected by the dimensional size of channel and flow rate. Besides, the void fraction at transitional points from churn-turbulent (slug) to annular flow are 0.66-0.67, which are independent with the gap size. Furthermore, a new criteria of slug to churn-turbulent flow is established in this study. In addition, by introducing the interfacial force model, the criteria of churn-turbulent (slug) flow to annular flow is verified.