• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1986-1991
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• 2003

To research on change of blade row flow field with tip clearance caused by upstream periodic wake, an apparatus that generate periodic wake through traversing cylinders were installed. Then how movement of upstream wake affect cascade flow and tip leakage flow were measured. Cylinder was installed in front of 50% of chord length, and traversing velocity was calculated at approximately 11.7m/s regarding inlet velocity and chord length. To measure three-dimensional velocity of flow inside blade row, single slanted hot-wire was used. From the results, when the periodic wake is inserted, the flow inside of cascade is dominantly affected by vortex that is generated from cylinder. This periodic wake affects passage vortex and tip leakage vortex.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.680-685
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• 2000

Liquid flow in a stirring mixer driven by a six-blade turbine has been investigated experimentally. The flows were quantified by measurements of velocity characteristics. obtained by a Particle Image Velocimetry(PIV). for a blade rotational speed of 100r.p.m. and for two blade clearances from the bottom of the tank. The instantaneous flow fields show that the bulk flow consists of small scale vortices very complicately. However, the mean flow results show that the formation of ring vortices above and below the blade. which depend on the clearance.

• YAKHAK HOEJI
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• v.28 no.3
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• pp.149-160
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• 1984

In order to certify the diuretic mechanism of dopamine, this study was performed in dog. The following results were obtained. Dopamine, when given intravenously, produced diuresis, and increased glomerular filtration rate (GFR), renal plasma flow (RPF), and amount of sodium excreted in urine. When infused directly into a renal artery, dopamine elicited a marked diuresis confined only to the infused side, with concomitant rises in osmolar clearance and sodium excretion as well as a slight increase in free water clearance. Simultaneously total renal plasma flow and medullary plasma flow increased markedly with a increase of glomerular filtration rate and renal plasma flow. Medullary concentration gradient of sodium also markedly lowered in the infused kidney. These changes were not observed during mannitol diuresis and renal action of dopamine were not apparent in dog pretreated with haloperidol. From the above experimental results, it is thought that dopamine, when given into a vien or infused directly into a renal artery, induces diuresis, and the mechanism of its action is due to dual actions which are hemodynamic effect along with glomerular filtraction rate, and the increased response in the medullary blood flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.357-363
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• 2016

In this study, we perform a series of aero-thermo-mechanical analyses to predict the running-tip clearance and the effects of impeller deformation on the performance using a centrifugal compressor. During operation, the impeller deformation due to a combination of the centrifugal force, aerodynamic pressure and the thermal load results in a non-uniform tip clearance profile. For the prediction, we employ the one-way fluid-structure interaction (FSI) method using CFX 14.5 and ANSYS. The predicted running tip clearance shows a non-uniform profile over the entire flow passage. In particular, a significant reduction of the tip clearance height occurred at the leading and trailing edges of the impeller. Because of the reduction of the tip clearance, the tip leakage flow decreased by 19.4%. In addition, the polytrophic efficiency under operating conditions increased by 0.72%. These findings confirm that the prediction of the running tip clearance and its impact on compressor performance is an important area that requires further investigation.

• Tribology and Lubricants
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• v.31 no.4
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• pp.148-156
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• 2015

In the study, a design process for ensuring optimal clearance in a fuel injection pump(FIP) is suggested. Structure analysis and hydrodynamic lubrication analysis are performed to determine the optimal clearance. The FIP is simulated using Hypermesh, Abaqus 6.12 to evaluate the reduction of clearance when the maximum supply pressure is applied. The reduction in clearance is caused by the difference in the deformations between the barrel and plunger. When the deformation of the plunger is larger than that of the barrel, a reduction in clearance at the head part occurs. On the other hand, the maximum clearance reduction equals the maximum deformation in the stem part, because the deformation of barrel does not occur in this region. The clearance of FIP should be designed to be larger than maximum reduction of clearance in order to avoid contact between the plunger and barrel. In addition, the two-dimensional Reynolds equation is used to evaluate lubrication characteristics with variations of viscosity, clearance and nozzle for a laminar, incompressible, unsteady state flow. The equation is discretized using the finite difference method. The lubrication characteristics of FIP are investigated by comparing film parameter, which is the ratio of the minimum film thickness and surface roughness. The optimal clearance of FIP is to be designed by considering the maximum reduction in clearance, lubrication characteristics, machining limits and tolerance of clearance.

• The KSFM Journal of Fluid Machinery
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• v.7 no.5 s.26
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• pp.36-42
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• 2004

The effect of tip clearance height on the three-dimensional flow and aerodynamic loss in the wake region of a high-turning turbine rotor cascade has been investigated with a miniature cone-type five-hole probe. Distributions of velocity magnitude, secondary velocity vectors, and total-pressure loss coefficient are presented for three tip gap-to-span ratios of h/s = 0.0, 0.5 and 1.0 percent. The result shows that with the increment of h/s, tip leakage vortex tends to be intensified and aerodynamic loss due to the leakage vortex is increased as well. In the case of h/s = 1.0 percent, aerodynamic loss in the tip-leakage flow region is found dominant in comparison with that in the passage vortex region. With increasing h/s, mass-averaged secondary loss coefficient has a greater portion in the mass-averaged total-pressure loss coefficient.

• The KSFM Journal of Fluid Machinery
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• v.4 no.1 s.10
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• pp.30-37
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• 2001

The experimental study on the effect of axial clearance between the tip of impeller blades and stationary shroud has been performed. The investigated compressor, which is a part of a small auxiliary power unit engine, consists of a curved inlet, a centrifugal impeller, a channel diffuser and a plenum chamber. It was designed for a total pressure ratio of 4.3 and an efficiency of $77\%$ at design speed of 60,000 rpm. The experiments are carried out in an open-loop centrifugal compressor test rig driven by a turbine. For the four different clearance ratios Cr(clearance/impeller tip width) of 6.25, 10.93, 15.60 and 20.30 percent, the overall performance data are obtained at $97\%,\;90\%$ and $80\%$ of the design speed. The results show the overall pressure ratio decrease of $7.7\%$ and the efficiency loss of $8.7\%$ across the variation of clearance ratio near the design speed. It also indicates that the influence of tip clearance became weaker as the flow rate is reduced and the stable operating range is not significantly influenced by the change of clearance ratio.

• Journal of computational fluids engineering
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• v.2 no.2
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• pp.18-25
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• 1997

A pressure-based Navier-Stokes numerical solver was used to compare solutions of the k-ε/RNG k-ε turbulence models. An efficient grid generation scheme, the transient grid generation with full boundary control, was used to solve the flows in the tip clearance region. Results indicate that the calculations using k-ε model captures various phenomena related to the tip clearance with good accuracy.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.04b
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• pp.153-157
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• 1996

A restrict jetting air is applied against leakage flow to improve a sealing performance of conventional labyrinth seal. A CFD analysis and sealing experiment are introduced to evaluate a sealing performance of applied model. The base of enhanced sealing is explained as a reducing clearance effect by jetting air. As a result, the applied model can improve the sealing performance of labyrinth seal in spite of the wide leakage clearance.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.195-199
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• 2001

The flow turning process, an incremental forming process, is a cost-effective forming method for axi-symmetric intricate parts to net shape. However, the flow turning process shows a fairly complicated deformation, it is very difficult to obtain satisfactory results. Therefore extensive experimental and analytical research has not been carried out. In this study, an fundamental experiment was conducted to improve productivity with process parameters such as tool path, angle of roller holder($\alpha$), feed rate(v ) and comer radius of forming roller(Rr). These factors were selected as variables in the experiment because they were most likely expected to have an effect on spring back. The clearance was controlled in order to achieve the precision product which is comparable to deep drawing one. And also thickness and diameter distributions of a multistage cup obtained by flow turning process were observed and compared with those of a commercial product produced by conventional deep drawing.