• International Journal of Naval Architecture and Ocean Engineering
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• v.1 no.2
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• pp.101-107
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• 2009

The VIV (Vortex-Induced Vibration) analysis of a flexible cylindrical structure under locally strong shear flow is presented. The model is made of Teflon and has 9.5m length, 0.0127m diameter, and 0.001m wall thickness. 11 2-dimensional accelerometers are installed along the model. The experiment has been conducted at the ocean engineering basin in the University of Tokyo in which uniform current can be generated. The model is installed at about 30 degree of slope and submerged by almost overall length. Local shear flow is made by superposing uniform current and accelerated flow generated by an impeller. The results of frequency and modal analysis are presented.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.4
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• pp.230-238
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• 2011

The experimental study for the performances of 100 kW marine current turbines (Horizontal Axis Turbine) has been conducted with three cases of 700 mm diameter model in PNU 100 m towing tank. Three cases of impeller have been designed according to the variation of section configuration and tip shape. The model tests have been carried out at different speed of revolution to find out the scale effect (Reynolds number effect). The designed rake impeller was the best among them in the efficiency point of view especially at high Tip Speed Ratio (TSR). The present study is expected to be extended to conduct at high reynolds number as well as the computational study for the validation.

• International Journal of Fluid Machinery and Systems
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• v.6 no.1
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• pp.11-17
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• 2013

Mini centrifugal pumps having a diameter smaller than 100mm are employed in many fields. But the design method for the mini centrifugal pump is not established because the internal flow condition for these small-sized fluid machines is not clarified and conventional theory is not suitable for small-sized pumps. Therefore, mini centrifugal pumps with simple structure were investigated by this research. Splitter blades were adopted in this research to improve the performance and the internal flow condition of mini centrifugal pump which had large blade outlet angle. The original impeller without the splitter blades and the impeller with the splitter blades were prepared for an experiment. The performance tests are conducted with these rotors in order to investigate the effect of the splitter blades on performance and internal flow condition of mini centrifugal pump. On the other hand, a three dimensional steady numerical flow analysis is conducted with the commercial code (ANSYS-CFX) to investigate the internal flow condition in detail. It is clarified from experimental results that the performance of the mini centrifugal pump is improved by the effect of the splitter blades. Blade-to-blade low velocity regions are suppressed in the case with the splitter blades and total pressure loss regions are decreased. The effects of the splitter blades on the performance and the internal flow condition are discussed in this paper.

• Applied Chemistry for Engineering
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• v.4 no.3
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• pp.537-543
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• 1993

The effect of agitation on liquid-liquid dispersion was investigated in an immisible liquid phase(n-hexane/water) system. Four different types of six-bladed turbine impellers were used: a flat blade, two screen blades and a solid edged 60 mesh screen blade. We found that the extent of dispersion of organic phase and power consumption of agitator were decreased in the order of flat, solid edged, 60 mesh, and 40 mesh blades at same agitation speed. And the minimum agitation speed for complete dispersion of organic phase was increased with increasing volume fraction of organic phase. Also, mean diameter of liquid droplets of dispersed phase was decreased with increasing agitation speed and it was increased in the order of solid edged, flat, 60 mesh, and 40 mesh screen blades at same agitation speed. At complete dispersion, the minimum power consumption was not vary significantly with impeller blade types, but the solid edged screen blade impeller gave the smallest and uniform sizes of liquid droplets, and it had a good performance for liquid-liquid dispersion. In this condition, Power number was not affected by Reynolds number and it was constant in turbulent flow region, and Sauter mean diameter($d_{32}$) of liquid droplets was expressed as a function of volume fraction of organic phase(${\phi}$) and Weber number($N_{We}$) as follows: $d_{32}/D=a(1+b{\phi})N_{We}{^{-0.6}}$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.11
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• pp.727-736
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• 2016

In this study, a high-pressure multistage pump used in the combined cycle power plants is analyzed. The pump performance characteristics (differential head and efficiency) are numerically analyzed for different shapes of the radial diffuser. The design variables selected for the radial diffuser are, number of vanes, diameter ratio ($D_4/D_3$), return channel outlet angle(${\alpha}_6$), and pressure recovery factor ($C_p$). The numerical analysis results showed that the differential head and efficiency are the highest when the diameter ratio is the highest. Further, it was observed that the differential head was lower when the return channel outlet angle was $60^{\circ}$ than when it was $90^{\circ}$, because of pre-swirl at the diffuser outlet.

• Tribology and Lubricants
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• v.36 no.5
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• pp.253-261
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• 2020

In this paper, we present an experimental investigation of the frequency characteristics and a visual inspection of an oxidizer pump with a modified rear-floating ring seal for a 7-tonf turbopump. An oxidizer pump typically operates at high rotational speeds and under cryogenic conditions. Despite its low hydraulic efficiency, the floating ring seal is frequently employed as a leakage control solution for turbomachinery because it effectively reduces abrasion by friction. When the oxidizer pump starts up, the floating ring moves excursively but locks up stably against the pump casing when the contact pressure increases. The compressive force on the floating ring depends on the hydrodynamic forces induced by the flow through the floating ring. This force is controlled by the nose position of the floating ring. Based on a validation test for a 7-tonf turbopump with two types of floating rings, we concluded that the floating ring with a small diameter nose can move easily with a low contact pressure in the cooling path. This leads to instability of the pressure fluctuation around the floating ring. In contrast, a floating ring with a large diameter nose has a high contact pressure and attaches strongly to the casing, which causes wear and frictional oxidation between the contact surfaces of the impeller and the floating ring.

• International Journal of Fluid Machinery and Systems
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• v.8 no.1
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• pp.46-54
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• 2015

Thrust-ring-pump is a kind of extreme-low specific speed centrifugal pump with special structure as numerous restrictions from thrust bearing and operation conditions of hydro-generator units. Because the oil circulatory and cooling system with thrust-ring-pump has a lot of advantages in maintenance and compactness in structure, it has widely been used in large and medium-sized hydro-generator units. Since the diameter and the speed of the thrust ring is limited by the generator set, the matching relationship between the flow passage inside the thrust ring (equivalent to impeller) and oil bath (equivalent to volute) has great influence on hydrodynamic performance of thrust-ring-pump. On another hand, the head and flow rate are varying with the operation conditions of hydro-generator units and the oil circulatory and cooling system. As so far, the empirical calculation method is employed during the actual engineering design, in order to guarantee the operating performance of the oil circulatory and cooling system with thrust-ring-pump at different conditions, a collaborative hydrodynamic design and optimization is purposed in this paper. Firstly, the head and flow rate at different conditions are decided by 1D flow numerical simulation of the oil circulatory and cooling system. Secondly, the flow passages of thrust-ring-pump are empirically designed under the restrictions of diameter and the speed of the thrust ring according to the head and flow rate from the simulation. Thirdly, the flow passage geometry matching optimization between thrust ring and oil bath is implemented by means of 3D flow simulation and performance prediction. Then, the pumps and the oil circulatory and cooling system are collaborative hydrodynamic optimized with predicted head-flow rate curve and the efficiency-flow rate curve of thrust-ring-pump. The presented methodology has been adopted by DFEM in design process of thrust-ring-pump and it shown can effectively improve the performance of whole system.

• Korean Journal of Materials Research
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• v.26 no.3
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• pp.136-142
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• 2016

To study the dispersion factors of silica sol prepared from fumed silica powder, we prepared silica sol under an aqueous system using a batch type bead mill. The dispersion properties of silica sol have a close relationship to dispersion factors such as pH, milling time and speed, the size and amount of zirconia beads, the solid content of fumed silica, and the shape and diameter of the milling impellers. Especially, the silica particles in silica sol were found to show dispersion stability on a pH value above 7, due to the electrostatic repulsion between the particles having a high zeta potential value. The shape and diameter of the impellers installed in the bead mill for the dispersion of fumed silica was very important in reducing the particle size of the aggregated silica. The median particle size ($D_{50}$) of silica sol obtained after milling was also optimized according to the variation of the size and amount of the zirconia beads that were used as the grinding medium, and according to the solid content of fumed silica. The dispersion properties of silica sol were investigated using zeta potential, turbiscan, particle size analyzer, and transmission electron microscopy.

• The KSFM Journal of Fluid Machinery
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• v.10 no.3 s.42
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• pp.17-24
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• 2007

This paper presents the design procedure of a vertical wind turbine named jet-wheel-turbo turbine and the numerical and experimental verifications. The design parameters such as the rotor inlet angle, the diameter-to-hub ratio, the inlet guide outlet angle and the solidity were optimized to maximize the energy transfer, and to further increase the turbine efficiency by applying the side guide vane and the side opening to the rotor. The maximum power coefficient of 0.59, which is much higher than the ever-designed three-bladed horizontal turbines, was experimentally obtained when the optimal inlet- and side-guide vanes were installed and both sides of the rotor were 80% opened. The maximum power coefficients occur at the tip speed ratio ranging between 0.6 and 0.7. This vertical-axis turbine model can be applied to the large-scale power generation system with the speed and torque control algorithm for the specified wind characteristics.

• Journal of ILASS-Korea
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• v.7 no.3
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• pp.38-44
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• 2002

The purpose of this study is to investigate the effect of the volume fraction of water and injection pressure on the spray characteristics of water/oil emulsified fuel injected from the pressure swirl atomizer. The mixture of light oil and water by using impeller mixer was performed. The spray characteristics such as SMD and velocity were measured using PDPA. The injection pressures were 7.5, 100, 200 and $300kgt/cm^2$ and volume fractions of water in emulsified fuel were 0, 10, 20 and 30%, respectively. The measurement sections were at 30, 60 and 90mm from injection nozzle tip. SMD and velocity of emulsified fuel were larger gradually by increasing the volume fraction of water in emulsified fuel. The spray angle was decreased and axial velocity was increased with increase in water content. It was found that the relative SMD ratio was increased more greatly than the relative axial velocity ratio in super critical pressure. The relative SMD ratio was increased and the relative axial velocity ratio was decreased with increase injection pressure at spray downstream.