• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.979-989
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• 2004

Numerical simulations have been performed to investigate tip clearance effect on through-flow and performance of a centrifugal compressor which has the same configuration of impeller with six different tip clearances. Secondary flow and loss distribution have been surveyed to understand the flow mechanism due to the tip clearance. Tip leakage flow strongly interacts with mainstream flow and considerably changes the secondary flow and the loss distribution inside the impeller passage. A method has been described to quantitatively estimate the tip clearance effect on the performance drop and the efficiency drop. The tip clearance has caused specific work reduction and additional entropy generation. The former, which is called inviscid loss, is independent of any internal loss and the latter, which is called viscous loss, is dependent on every loss in the flow passage. Two components equally affected the performance drop as the tip clearances were small, while the efficiency drop was influenced by the viscous component alone. The additional entropy generation was modeled with all the kinetic energy of the tip leakage flow. Therefore, the present paper can provide how to quantitatively estimate the tip clearance effect on the performance and efficiency.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.240-247
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• 1998

Leakage vortices formed near blade tip causes an increase of total pressure loss near casing endwall region and as a result, the efficiency of rotor decreases. The reduction of rotor efficiency is related to the size of tip clearance. In this study, the three-dimensional flowfields in an axial flow rotor were calculated with varying tip clearance under various flow rates, and the numerical results were compared with experimental ones. The effects of tip clearance and attack angle on the leakage vortex and overall performance, and the less distributions were investigated through numerical calculations. In this study, tip leakage flow rate and total pressure loss by tip clearance were evaluated using numerical results and aprroximate equations were presented to evaluate the reduction of rotor efficiency by tip leakage flow.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.5
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• pp.795-804
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• 2015

Tip clearance loss is a limitation of the improvement of turbomachine performance. Previous studies show the Tip clearance loss is generated by the leakage flow through the tip clearance, and is roughly linearly proportional to the gap size. This study investigates the tip clearance effects on the performance of ducted propeller. The investigation was carried out by solving the Navier-Stokes equations with the commercial Computational Fluid Dynamic (CFD) code CFX14.5. These simulations were carried out to determine the underlying mechanisms of the tip clearance effects. The calculations were performed at three different chosen advance ratios. Simulation results showed that the tip loss slope was not linearly at high advance due to the reversed pressure at the leading edge. Three type of vortical structures were observed in the tip clearance at different clearance size.

• The KSFM Journal of Fluid Machinery
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• v.2 no.1 s.2
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• pp.73-80
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• 1999

Leakage vortices formed new blade tip causes an increase of total pressure loss near the casing endwall region and as a result, the efficiency of rotor decreases. The reduction of rotor efficiency is related to the size of the tip clearance. In this study, the three-dimensional flowfields in an axial flow rotor were calculated by varying the tip clearance under various flow rates, and the numerical results were compared with experimental ones. The effects of tip clearance and attack angle on the leakage vortex and overall performance, and the loss distributions were investigated through numerical calculations. In this study, tip leakage flow rate and total pressure loss by tip clearance were evaluated using numerical results and approximate equations were presented to evaluate the reduction of rotor efficiency by tip leakage flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.6
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• pp.813-821
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• 1997

Three-dimensional turbulent incompressible flow through the tip clearance of a linear turbine rotor cascade with high turning angle has been analyzed numerically. As a preliminary study to predict the tip clearance loss realistically, a generalized k-.epsilon. model derived by RNG (renormalized group) method is used for the modeling of Reynolds stresses to account for the strain rate of turbulent flow. The effects of the tip clearance flow on the passage vortex, the total pressure loss are considered qualitatively. The existences of vena contract and tip clearance vortex have been confirmed and it has been shown that as the size of the tip clearance increases, the accumulated flow through the tip clearance and the total pressure loss downstream of the cascade increase.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.9
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• pp.1113-1120
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• 1999

Leakage vortices fonned near the blade tip cause an increase of total pressure loss near the casing endwall region and as a result, the efficiency of rotor decreases. The reduction of rotor efficiency is related to the size of tip clearance. In this study, the three-dimensional flow fields in an axial flow rotor were calculated with varying tip clearance under various flow rates, and the numerical results were compared with experimental ones. The effects of tip clearance and the of attack on the leakage vortex and overall performance, and the los9 distributions were investigated through numerical calculations. In this study, tip leakage flow rate and total pressure loss due to the tip clearance were evaluated using numerical results and approximate equations were presented to evaluate the reduction of rotor efficiency due to the tip leakage flow.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.33-36
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• 2010

Lots of studies about turbine loss have been done especially about tip leakage loss. But these studies deals with small tip clearances which is less than 5 percent chord. Now, like turbopumps, small turbines have larger tip clearance and it is hardly found related papers in open literature. On this study, with varying tip clearance 1% to 20% chord, loss is measured under inlet velocity at 30m/s and Reynolds number based on chord at 210000. It is found that maximum loss coefficient is 0.113 at 10% clearance, and when tip clearance is larger than 10%, loss is not linearly increased anymore.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.389-397
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• 2003

Effect of tip leakage flow on through flow and performance of a centrifugal compressor impeller was numerically studied using CFX-TASC flow. Seven different tip clearances were used to consider the influence of tip clearance on performance. Secondary flow and loss factor were evaluated to understand the loss mechanism inside the impeller due to tip leakage flow. The calculated results were circumferentially averaged along the passage and at the impeller exit for quantitative discussion. Tip clearance effect on Performance could be decomposed into inviscid and viscous components using one dimensional equation. The inviscid component is related with the specific work reduction and the viscous component is related with the additional entropy generation. Two components affected Performance equally. while efficiency drop was mainly influenced by viscous loss. Performance and efficiency drop due to tip clearance were proportional to the ratio of tip clearance to exit blade height. A simple model suggested in the present study predict performance and efficiency drop quite successfully.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.240-243
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• 2008

In this paper, the design of Centrifugal Compressor which is used in sizes 50 horse power has 8 pressure ratio and numerical analysis of the flow within compressor varying tip clearance length are performed. To get high pressure ratio with low power the exit height of impellers is low but compressor has very high speed of revolution. So compressor has high specific speed although mass flow rate is very small. The shape of impellers at the first stage is carried out. Flow and performance characteristics of impellers has been analyzed by using a commercial CFD program, $Fine^{TM}$/turbo. The result shows that loss coefficient is affected by tip clearance length and compressor has proper tip clearance length. It is possible to decrease loss by selecting apt tip clearance length.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.145-148
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• 2008

Korea Aeronautics Research Institute (KARI) is developing a turbo pump that has 1-stage impulse turbine and relatively high tip clearance for safety. The objective of this research is to investigate the effect of reaction on tip clearance loss in axial turbines. Both cascades were tested in a subsonic wind tunnel. In each cascade, total pressure was measured for tip clearance ranging from 1% to 20% of chord. In results, increasing tip clearance, total pressure loss in reaction turbines is continually increased but impulse turbines keep almost same level of mass averaged total pressure loss. When tip clearance becomes more than 10% of chord, mass-averaged total pressure loss in impulse turbines is less than in reaction. This means that when tip clearance is more than 10% of chord, impulse turbines have better efficiency than reaction turbines.