• The KSFM Journal of Fluid Machinery
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• v.10 no.1 s.40
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• pp.34-40
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• 2007

In this study, the characteristic of a vane pump of automotive power steering system is numerically analyzed. The vane pump changes the energy level of operation fluid by converting mechanical input power to hydraulic output. To simulate this mechanism, moving mesh technique is adopted. As a result, the flow rate and pressure are obtained by numerical analysis. The flow rate agrees well with the experimental data. Moreover, the variation and oscillation of the pressure around the rotating vane are observed. As a result of flow characteristics, The difference of pressure between both side of vane tip causes the back flow into the rotor. As the rotational velocity increases, the flow rate at the outlet and the pressure in the vane tip rises with higher amplitude of oscillation. In order to reducing the oscillation, the design of devices for decreasing the cross-area of the outlet part and returning the flow from the outlet to the inlet is required.

• The KSFM Journal of Fluid Machinery
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• v.16 no.5
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• pp.24-28
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• 2013

Visualization of internal flow of a regenerative blower has been made by injecting a tracer directly into the flow. For the convenience of visualization, working fluid has been replaced by water and marbling color oil has been used as a tracer. Oil droplet has been injected near the inlet of the blower and the streak has been recorded using a high speed camera with the illumination of high power light sources. At first, droplets have irregular motion in the near inlet area and enter into a groove of the impeller. Then the droplets circulate inside the groove while translated by the rotational motion of the impeller. When the droplets get out of the impeller groove, their speed is lower than that of impeller. And the droplets repeatedly enter into the groove and circulate inside the grooves. Then the droplets either flow to the outlet or reenter into the inlet area through stripper. Through this experimental study, internally circulating motion of the flow inside a regenerative blower has been characterized.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1543-1551
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• 2001

The characteristics of starting flow of a six-blade Rushton turbine mixer were investigated by using a cinematic Particle Image Velocimetry technique. The flows were quantified by measurements of velocity fields with a 4 ms time interval for a blade rotational speed of 100 r.p.m, so that the turbine Reynolds number(ND$^2$/ ν) was fixed to 6,960. The radial shedding of the trailing vortices starts from passing four blades after the beginning of rotation. It clearly shows that the vortex pairing phenomena caused by the interactions between trailing cortices firm consequtive blades. The average convection velocity of the radial flow is found to be 28 % of the tip velocity. The starting flow seems to arrive at a steady state after 8 revolutions in this study, which corresponds nearly one circulation through the bulk flow trajectory with the average radial convection velocity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.7 s.238
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• pp.784-794
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• 2005

In the very low specific speed range ($n_s=0.24$ < 0.25, non-dimensional), the efficiency of centrifugal pump designed by a conventional method is very low in common. Therefore, positive-displacement pumps have long been used widely. Recently, since the centrifugal pumps are becoming higher in rotational speed and smaller in size, there expects to develop a new centrifugal pump with a high performance to replace the positive-displacement pumps. The purpose of this study is to investigate the internal flow characteristics of a very low specific speed centrifugal pump and to examine the effect of internal flow pattern on pump performance. The results show that the theoretical head definition of semi-open impeller should be revised by the consideration of high slip factor in the semi-open impeller, and the leakage flow through the tip clearance results in a large effect on the impeller internal flow. Strong reverse flow at the outlet of semi-open impeller reduces the absolute tangential velocity considerably, and the decreased absolute tangential velocity increasese the slip factor with the reduction of theoretical head.

• International Journal of Fluid Machinery and Systems
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• v.3 no.4
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• pp.271-278
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• 2010

Small-sized axial fans are used as air cooler for electric equipments. But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is conducted, although, it causes the deterioration of efficiency and the increase of noise. Then the adoption of contrarotating rotors for the small-sized axial fan is proposed for the improvement of performance. In the present paper, the performance curves of the contra-rotating small-sized axial fan with 100mm diameter are shown and the velocity distributions at a partial flow rate at the inlet and the outlet of each front and rear rotor are clarified with experimental results. Furthermore, the flow conditions between front and rear rotors of the contra-rotating small-sized axial fan are investigated by numerical analysis results and causes of the performance deterioration of the contra-rotating small-sized axial fan at the partial flow rate is discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.1
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• pp.89-95
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• 2015

A surge phenomenon cause noise and pulsations in a turbo compressor, which is an unstable operating regime. Because surge protection ensures a safe compressor operation, it is important to understand the physics of the surge phenomenon. In this study, the surge characteristics of a 250-hp class turbo-compressor were evaluated experimentally. The experimental parameters were the rotational speed, opening angles of the inlet guide vane and exit valve, and inlet pipe diameter and flow rates of the inlet gases. The results showed that the compressor surge was very sensitive to the gas flow rates, exit pressure, rotational speed, and bypass flow rates.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.5
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• pp.62-70
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• 2015

A liquid rocket engine system can cause rapid pressure and temperature variations during the startup period. Thus the startup analysis is required to reduce time and expense for successful development of liquid rocket engine through the startup prediction. In this study, a startup analysis simulator is developed for a staged combustion cycle engine powerpack. This simulator calculates propellant flow rates using pressure and flow rate balances. In addition, a rotational speed of turbopump is obtained as a function of time by mathematical modeling. A startup analysis result shows that the time to reach a steady-state and a rotational speed at the steady-state are 1.3 sec and 27,500 rpm, respectively. Moreover it can indicate proper startup sequences for stable operation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.544-549
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• 2017

This paper aims to examine the effect of rotational fluid motion about the efficiency of the gas - liquid ejector, which is a core unit in a ship equilibrium water treatment system. The ejector is a device for injecting ozone into ship equilibrium by the negative pressure generated by exchange of momentum between water and ozone. The existing ejector ejects the driving fluid with a simple form. In this paper, however, a rotation induction device is applied to the driving nozzle so that the driving fluid can be rotated and injected. To investigate the flow characteristics by the rotational movement of the driving fluid, CFD was used. The pressure and flow rate of the driving fluid, the negative pressure and suction flow rate of the suction fluid in the suction part, and the discharge pressure were predicted. On the basis of the results, the efficiency of the ejector using the rotation induction system was 22.25%, which was about 1.7% better than that of the existing ejector. Finally, to verify the feasibility of the CFD, an experiment was conducted on the ejector using the rotation induction device and the results were similar to those of the CFD.

• KIEE International Transactions on Electrophysics and Applications
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• v.4C no.4
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• pp.155-159
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• 2004

This work reports the theoretical and experimental investigations of capillary bust valves to regulate liquid flow in microchannels. The theoretical analysis uses the Young-Laplace equation and geometrical considerations to predict the pressure at the edge of the valve opening. Numerical simulations are employed to calculate the meniscus shape evolution while the interface is pinned at the valve edge. Microchannels and valves are fabricated using soft lithography. A wafer-rotating system, which can adjust the driving pressure by rotational speed, induces a liquid flow. Experimentally measured valve-bursting pressure agrees with theoretical predictions.

• International Journal of Fluid Machinery and Systems
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• v.6 no.3
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• pp.144-151
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• 2013

In this paper, the design method of a low-head propeller-type hydro turbine is studied for various numbers of blades on an axial propeller. We also investigate the relationship between geometrical parameters and internal performance parameters, such as angular velocities (100, 200, 300, 400 rpm) and 2.5~4m low heads through a three-dimensional numerical method with the SST turbulent model. The numerical results showed that the blade number had a more dominant influence than the change in heads and rotational speed on the flow characteristics of the turbine. The distributions of pressure and velocity in the streamwise direction of the propeller turbine were graphically depicted. Especially, the relationship among dimensionless parameters like specific speed ($N_s$), flow coefficient (${\phi}$) and power coefficient (P) were investigated.