• The KSFM Journal of Fluid Machinery
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• v.13 no.1
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• pp.23-28
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• 2010

A draft tube which has impeller to elevate bottom water and spread it over surface of lake water, induces convective circulation of lake water, a Long-Distance Circulation (LDC). Circulation of lake water make stratified water mixed and enhance DO (Dissolved Oxygen) of bottom water. Circulation rate of water is determined by draft rate of the tube, which is dependent on design parameters of the draft tube system, i. e. dimension of impeller and diffuser, inclined angle of impeller, impeller shape, and rotational speed. In this study, change in draft rate and power consumption of circulation equipment was investigated numerically with changing impeller dimension, angle and rotational speed. It was found that flowrate of draft water was increased as the dimensions of draft tube and impeller, and rotational speed and inclined angle of impeller increased. The power consumption was also elevated with increasing parameter values, and final selection of parameter values was made to satisfy target flowrates and power consumption.

• Journal of Astronomy and Space Sciences
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• v.25 no.4
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• pp.415-424
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• 2008

Kwak et al. (2008) found that the mean neutral wind pattern in the high-latitude lower thermosphere is dominated by rotational flow than by divergent flow. As an extension of the our previous work (Kwak et al. 2008), we performed a term analysis of vorticity equation that describes the driving forces for the rotational component of the horizontal wind in order to determine key processes that causes strong rotational flow in the high-latitude lower thermospheric winds. For this study the National Center for Atmospheric Research Thermosphere-Ionosphere Electrodynamics General Circulation Model (NCAR-TIEGCM) is used. The primary forces that determine variations of the vorticity are the ion drag term and the horizontal advection term. Significant contributions, however, can be made by the stretching term. The effects of IMF on the vorticity forces are seen down to around 105-110km.

• Journal of the Korean Society of Industry Convergence
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• v.6 no.1
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• pp.49-56
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• 2003

Based on the flow patterns of cylindrical vessel, the flow patterns of conical vessel, spherical vessel, rectangular vessel and cylindrical vessel with baffles were visualized by a trace method using aluminum powder. In addition, the correlations of the critical circulating frequency for mixing were derived from the experimental results. The conical and spherical vessels which have circular cross sections were same effective as cylindrical vessel for the shake mixing due to developing the rotational flow. Both a rectangular vessel and a cylindrical vessel with baffles should not be adapted for shake mixing because of not developing rotational flows in these type of vessels.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.13-19
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• 1995

An experimental investigation has been made for flow in a circular cylinder with a rotating bottom disk. Flow system considered in this paper is a characteristic model of interior flows of an electric washing machine. Flows in a tub of an electric washing machine are driven by a rotating bottom disk called a pulsator. The simple and characteristic model was composed of a circular cylinder with impulsively rotating endwall disk and a viscous fluid in it. Rotational motion of the pulsator is periodic and alternative in rotation direction. The flow field in the interior region is governed by a horizontal boundary layer forms on the impulsively rotating disk. Experimental approach was accomplished by adopting an image processing technique for velocity measurements. Comprehensive details of the flow structure are presented. Also a meridional circulation is obtained by tracking image particles suspended in the fluid. Flow structure and data are successfully procured for this complex rotating flow field.

• Progress in Superconductivity and Cryogenics
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• v.26 no.1
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• pp.25-30
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• 2024

High-temperature superconducting rotors offer advantages in terms of output-to-weight ratio and efficiency compared to conventional phase conduction motors or generators. The rotor can be cooled by conduction cooling, which attaches a cryocooler, and by refrigerant circulation, which uses circulating liquid or gas neon, helium and hydrogen. Recent work has focused on environmental issues and on high-temperature superconducting motors cooled with liquid hydrogen that can be combined with fuel cells. However, to ensure smooth supply and return of the cryogenic cooling fluid, a cryogenic rotational coupling between the rotating and stationary parts is necessary. Additionally, the development of a sealing structure to minimize fluid leakage applicable to the coupling is essential. This study describes the design and performance evaluation of a non-contact sealing method, specifically a labyrinth seal, which avoids power loss and heat load caused by friction in contact sealing structures. The seal design incorporates a spiral flow path to reduce leakage using centrifugal force, and computational fluid dynamics (CFD) simulations were conducted to analyze the flow path and rotational speed. A performance evaluation device was configured and employed to evaluate the designed seal. The results of this study will be used to develop a cryogenic rotational coupling with supply and return flow paths for cryogenic applications.

• International Journal of Fluid Machinery and Systems
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• v.9 no.4
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• pp.325-331
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• 2016

A bathtub vortex above the outlet of a rotating barrel is simulated. By analyzing the Ekman layer theory, it can be found that the main flow circulation is inversely proportional to the thickness of Ekman layer. The thicker the Ekman boundary layer, the weaker the rotational strength and the shorter of the length of gas core is. According to this law, models of barriers with rods of different heights are established. The reduction of air-core length in this air entrainment vortex and weakening the strength of rotation field were achieved.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.1
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• pp.81-86
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• 2006

High temperature superconducting (HTS) power cable requires forced sub-cooled LN2 flow cooling. Liquid nitrogen is circulated by a pump and cooled back by cooling system. Typical operating temperature range is expected to be between 65 K and 77 K. The HTS power cable needs sufficient cooling to overcome its low temperature heat load. For successful cooling, the hydraulic characteristics of the HTS power cable must be well investigated to design the cables. Especially, the pressure drop in the cable is an important design parameter, because the pressure drop decides the length of the cable, size of the coolant circulation pump and circulation pressure, etc. This paper describes measurement and investigation of the pressure drop of the cooling system. In order to reduce the total pressure drop of the cooling system, the flow rate of liquid nitrogen must be controlled by rotational speed of the circulation pump.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.5
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• pp.507-515
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• 2015

This study was conducted to develop and verify a torque application device for use in a mechanical power-circulation test rig for 5.5 MW wind turbine gearboxes. The design and analysis of the torque application device was conducted. In addition, the torsional stiffness of the test rig was calculated using the rotational angle measurements for each of the components. The calculated stiffness of the test rig was $231.13kN{\cdot}m/rad$ for a clockwise torque application. The rated torque can be applied when the stiffness of the gearbox is greater than $1,064,400kN{\cdot}m/rad$ for a clockwise torque application. Because of the limited rotational angle of the test rig, the potential application of the rated torque is determined according to the torsional stiffness of the test gearbox.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.2
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• pp.200-206
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• 2015

In order to verify the lift enhancement of the 2D hydrofoil with trailing edge rotor and check the ability of its practical use, experimental studies were conducted in the caviation tunnel using the test model with NACA0020 section. The three-component forces acting on the model could be measured by exclusively designed sting type multi-component load cell. The trailing edge of the model has been replaced with rotor which could be controlled by DC servo motor installed at the exterior of the tunnel. A typical effect of the trailing edge rotor has been introduced among the systematic experiments on various angular deviation of the model and the rotational velocity of the trailing edge rotor. It is appeared that the circulation control effect could be easily adjusted by selecting the rotational velocity of the trailing edge rotor and the lift force was augmented more than two times. Thus the proposed lifting device could be utilized as a novel high lifting device which has adjustability of lift force.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.1
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• pp.10-17
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• 2007

Numerical results from the "figure-of-eight" motion of Phormia-Regina in Part 1 indicate that vortical structure and vortex dynamics do play a critical role in lift and thrust generation. The aerodynamic force generation of insects' wing could be governed by aerodynamic parameters such as Reynolds number; kinematic parameters such as frequency, amplitude, and component of the figure of eight motion; and morphological parameters such as wing shape and the number of wing. In the present work, the effects of Reynolds number, reduced frequency and motion component are investigated in detail to clarify aerodynamic characteristics of insect wing. Through numerical results and their physical interpretation, the mechanism of aerodynamic force generation is presented more clearly. Rotation turns out to be the most important component in thrust generation and subsequent counterclockwise rotational circulation is closely related with thrust generation.