• Journal of Mechanical Science and Technology
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• 제17권4호
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• pp.606-616
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• 2003

A numerical analysis has been conducted in order to simulate the characteristics of complex flow through linear cascades of high performance turbine blade with/without tip clearance by using a pressure-correction based, generalized 3D incompressible Wavier-Stokes CFD code. The development and generation of horseshoe vortex, passage vortex, leakage vortex, tip vortex within tip clearance, etc. are clearly identified through the present simulation which uses the RNG k-$\varepsilon$ turbulent model with wall function method and a second-order linear upwind scheme for convective terms. The present simulation results are consistent with the generally known tendency that occurs in the blade passage and tip clearance. A 3D model for secondary and leakage flows through turbine cascades with/without tip clearance is also suggested from the present simulation results, including the effects of tip clearance height.

• Journal of Mechanical Science and Technology
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• 제18권6호
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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.

• 한국융합학회논문지
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• 제8권10호
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• pp.193-199
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• 2017

기계적 태핏은 유압 태핏과 비교하여 원가와 마찰 손실을 줄일 수 있어 사용된다. 그러나 기계적 태핏은 캠과 밸브 사이의 간극을 조절하는 기능이 없으므로 밸브의 열팽창을 고려하여 캠과 밸브 사이의 거리를 측정하여 선정된다. 그러므로 충분한 워밍 업 후에는 밸브 간극이 거의 없지만 그 전에는 밸브 간극이 존재한다. 특히 냉간 작동 조건에서는 비교적 큰 편이고 소음과 진동 같은 문제를 발생시킬 수 있다. 본 논문에서는 밸브 간극을 변경시켜 가며 각각의 조건에서의 밸브 리프트, 속도, 가속도, 시팅 속도, 바운싱 높이 등에 대하여 시험과 해석을 통하여 연구되었다. 밸브 간극이 증가할수록 램프 구간이 감소하게 되어 밸브의 거동에 좋지 않은 영향을 미치는 것을 확인할 수 있었다.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2540-2549
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• 2022

For a pressurized water reactor power plant, the reactor coolant pump (RCP) is a kernel component. And for a canned motor RCP, the rotor system's properties determines its safety. The liquid coolant inside the canned motor RCP fills clearance between the metal shields of rotor and stator, forming a lengthy clearance flow. The influence of inlet preswirl on rotordynamic coefficients of clearance flow in canned motor RCP and their effects on the rotordynamic characteristics of the pump are numerically and experimentally investigated in this work. A quasi-steady state computational fluid dynamics (CFD) method has been used to investigate the influence of inlet preswirl. A vertical experiment rig has also been established for this purpose. Rotordynamic coefficients on different inlet preswirl ratios (IR) are obtained through CFD and experiment. Results show that the cross-coupled stiffness of the clearance flow would change significantly with inlet preswirl, but other rotordynamic coefficients would not change significantly with inlet preswirl. For the case of clearance flow between the stator and rotor cans, influence of inlet preswirl is not so significant as the IR is not large enough.

• 대한기계학회논문집B
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• 제21권6호
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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.

• Design & Manufacturing
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• 제14권2호
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• pp.7-13
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• 2020

For one decades, mobile devices components were made with plastic material, but environmental problems have recently replaced them with metal materials such as aluminum. Generally, aluminum components are mostly produced through cutting, but this process has limitations such as productivity and chip recycling. For this reason, many researches are conducted to improve productivity by replacing with the forging press process for manufacturing mobile device components. After forging process, the flash is remained and it is necessary to eliminate the flash from the final shape of components. In this paper, one-sided clearance for blanking aluminum material wes selected for parameter affected to the dimensional precision. Because the clearance is the most important parameter in blanking process. Deriving the clearance of blanking process for high dimensional precision, five level of one-sided clearance is selected and CAE is used to analyze the dimensional precision for each case.

• 대한기계학회논문집B
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• 제40권6호
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• pp.357-363
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• 2016

본 연구에서는 날개 두께 분포가 다른 두 임펠러를 이용하여 유체-구조 연성해석을 통해 운전익단간극을 예측하고 임펠러의 변형이 성능에 미치는 영향에 대해 연구하였다. 임펠러는 작동조건에서 작용하는 원심력, 압력, 열 하중의 영향으로 변형이 발생하게 된다. 이로 인해 초기 설계된 익단간극이 비균일하게 변화하는 것을 확인하였다. 특히 임펠러 날개의 선단과 후단에서 가장 큰 익단간극 감소가 발생하였으며, 이로인해 간극누설유동이 19.4% 감소하였다. 또한 운전조건에서 익단간극 감소로 간극누설 유량이 감소하면서 효율은 0.72% 증가하는 것을 확인하였다. 원심압축기 작동조건에서의 정확한 운전익단간극의 예측과 익단간극의 변화가 성능에 미치는 영향에 대해서 확인하였다.

• Structural Engineering and Mechanics
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• 제63권5호
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• pp.691-702
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• 2017

Clearances are essential for the assemblage of mechanisms to allow the relative motion between the joined bodies. This clearance exists due to machining tolerances, wear, material deformations, and imperfections, and it can worsen the mechanism performance when the precision and smoothly-working are intended. Energy is a subject which is less paid attention in the area of clearance. The effect of the clearance on the energy of a flexible slider-crank mechanism is investigated in this paper. A clearance exists in the joint between the slider and the coupler. The contact force model is based on the Lankarani and Nikravesh model and the friction force is calculated using the modified Coulomb's friction law. The hysteresis damping which has been included in the contact force model dissipates energy in clearance joints. The other source for the energy loss is the friction between the journal and the bearing. Initial configuration and crank angular velocity are changed to see their effects on the energy of the system. Energy diagrams are plotted for different coefficients of friction to see its influence. Finally, considering the coupler as a flexible body, the effect of flexibility on the energy of the system is investigated.

• Journal of Mechanical Science and Technology
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• 제14권2호
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• pp.226-235
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• 2000

The performance prediction of an airfoil fan using a commerical code, STAR/CD, is verified by comparing the calculated results with measured performance data and velocity fields of an airfoil fan. The effects of inlet tip clearance on performance are investigated. The calculations overestimate the pressure rise performance by about 10-25 percent. However, the performance reduction due to tip clearance is well predicted by numerical simulations. Main source of performance decrease is not only the slip factor but also impeller efficiency. The reduction in performance is 12-16 percent for 1 percent gap of the diameter. The calculated reductions in impeller efficiency and slip factor are also linearly proportional to the gap size. The span-wise distributions of phase averaged velocity and pressure at the impeller exit are strongly influenced by the radial gap size. The radial component of velocity and the flow angle increase over the passsage as the gap increases. The slip factor decreases and the loss increases with the gap size. The high velocity of leakage jet affects the impeller inlet and passage flows. With a larger clearance, the main stream moves to the impeller hub side and high loss region extends from the shroud to the hub.

• International Journal of Fluid Machinery and Systems
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• 제6권3호
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• pp.113-120
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• 2013

While performing numerical simulations, it is general industrial practice to neglect the clearance gap between the impeller and the inlet duct. In the present work, the effect of clearance gap on the performance of an industrial sized centrifugal blower is simulated for two volutes of width ratios and various flow coefficients. The results show that the clearance has a positive effect at low mass flow rates. This is observed in the pressure rise (1.3%) as well as in efficiency (0.7%). At higher mass flow rates, it has a negative effect with a drop in efficiency of 1% and pressure drop of about 1.4%. The effect of clearance gap on volute with higher width ratio is smaller when compared with the volute with smaller width ratio.