• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.497-500
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• 2000

절삭 작업과정에서 발생하는 버는 공구와 피삭재가 만나는 상태에 따라 그 형상이 결정되어진다. 공구와 피삭재 사이의 각, 공구의 회전속도, 이송속도, 피삭재의 종류등은 이러한 버의 형상을 결정하는데 결정적인 역할을 하므로, 실험에 의해서 생성된 단계별 자료를 CAD 및 CAM 데이터와 연관시켜 효율적인 알고리즘을 만들고자 한다. 특별히 공장자동화에 따른 작업의 자동화뿐 아니라 관리 체계의 정립을 위하여 전문가 시스템의 도입 역시 시급히 요구되고 있는 실정이다. 여기서 CAD 데이터는 피삭재에 대한 특징 형상의 정보를 포함하고 있기 때문에 피삭재의 형상에 대한 정보를 얻을 수 있다. 인식된 형상에 대하여 Exit 버 형성시 접점과 Exit Angle을 계산하기 위해 도형의 방향인식이 필요하며, 이를 통해 공구와 피삭재와의 관계를 산출하여 Exit 버의 판별을 수행할 수 있다. 본 논문에서는 이러한 과정을 수행하는 프로그램을 개발한다.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.525-530
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• 2000

The effects of vortex generators, in the form of small tabs projecting into the flow at the axisymmetric supersonic nozzle exit and triangular thin tapes attached on the inner surface at the nozzle exit, on the characterixtics of supersonic mixing enhancements are experimentally investigated. Delta-shaped tabs as small as 1% of the nozzle exit area produce strong counter-rotating vortices, and is found to produce significant effects on the jet flowfield downstream of the nozzle. The effects is larger on the under-expanded cases than over- and perfect-expanded cases. Nozzle inner surface roughness also can do a role of centerline pressure decay for highly under-expanded jet cases. The effects of the angle of tabs with respect to flow direction are also investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.134-137
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• 2014

The noise reduction performance of a passive facility is dependent on the its length or volume. In other words, this means that the larger the size of passive facility is, the better the noise reduction performance is. The sound directivity control has been proposed as an alternative for the noise reduction without a passive facility. The purpose of this study is to investigate the correlation between the flange attached to inclined exit of the tube and sound directivity when the sound radiates from the tube to the outside. As a result, the sound radiated from flanged tube had weak sound directivity in the wide angle. Also as the flange was bigger, the sound pressure level was lower in the behind the flange.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.1 s.232
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• pp.46-54
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• 2005

Film cooling characteristics has been examined numerically for the height variation of a stepped slot exit. In this study, the upstream wall height of the stepped slot exit varies from -2d (d = slot width) to 3d, blowing ratio ranges from 0.5 to 3, and injection angles are $15^{\circ},\;30^{\circ},\;and\;45^{\circ}$. The results showed that film cooling performance was mainly subjected to the magnitude of recirculation region near the downstream-side slot exit as well as the magnitude and the distribution region of turbulent kinetic energy due to the local velocity and momentum differences between the coolant and the main flow near the slot exit. The up-1d type slot at higher blowing ratios over 2 and the flat type slot at lower blowing ratios below 1 have the best film cooling performances, in case of the injection angles of $30^{\circ},\;and\;45^{\circ}$, respectively. Compared with the other injection angles, in case of the injection angles of $15^{\circ}$, the best film cooling performances was shown in even a higher upstream wall (up-3d) at higher blowing ratio like 3 by the gradual reduction of the coolant velocity which minimizes the local velocity differences between the coolant and the main flow near the slot exit.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.611-614
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• 2002

Rotating stall in vaneless diffusers of centrifugal compressor occurs in the diffuser wall due to flow separation at large inlet flow angle. For this reason, the critical inlet flow angles are suggested by several researchers. Beyond this critical angle, flow separates in the diffuser, and develops into rotating stall. This paper studied this critical flow angle. Rotating stall is measured through eight fast-response pressure transducers which are equally spaced around the circumference at the inlet and exit of a vaneless diffuser. Experiments are done from 20000rpm to 60000rpm for the diffuser stall. Two-cell structure which rotates at $6{\~}l0{\%}$ of impeller speed is fully developed at $20000{\~}40000rpm$, and three-cell structure which rotates at $7{\~}9{\%}$ of impeller speed is fully developed at $50000{\~}60000rpm$. This paper shows that the critical inlet flow angle is not constant but related with tip speed of impeller. As tip speed increases, so does the critical inlet flow angle.

• Journal of computational fluids engineering
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• v.21 no.1
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• pp.58-63
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• 2016

This research is to investigate the performance analysis for efficient design with four different inlet angles of the centrifugal pump impeller. Assuming that the rotation speed and exit angle are fixed, Four cases of the centrifugal pumps were numerically analyzed using ANSYS FLUENT. According to the numerical results, head and pump efficiency at inlet angle of 20 degrees was highest. There is no big difference of efficiency at inlet angle of 20 degrees compared to the inlet angle 30 degrees. About 15% of efficiency at inlet angle of 20 degrees is higher than inlet angle of 40 degrees and 31% higher than inlet angle oof 50 degrees. Because there is liner functional relationship between speed and flow rate, suction flow rate at inlet angle of 20 degrees is superior to the inlet angle of 30 degrees as much as 0.89%, inlet angle of 40 degrees as 13%, inlet angle of 50 as 28.4%. Head at inlet angle of 20 degrees is superior to the inlet angle of 30 degrees as much as 0.4%, inlet angle of 40 degrees as 2.7%, inlet angle of 50 degrees as 3.2%. There should exist highest efficiency and also optimal design shape at inlet angle of 20 degrees.

• The KSFM Journal of Fluid Machinery
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• v.16 no.2
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• pp.48-53
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• 2013

This paper presents a numerical investigation of the influence of the blade back sweep angle on the performance and flow characteristics in a centrifugal compressor with a vaneless diffuser. Five impellers with different back sweep angles were tested in the flow simulations. It was found that a low back sweep angle could improve the total-to-total pressure ratio and the work coefficient over whole operating ranges. However, the flow field in an impeller with a low back sweep angle produced a more non-uniform velocity distribution at the impeller exit because the wake region was significantly increased. As a consequence, the impeller with a low back sweep angle caused a low diffuser performance.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.422-427
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• 2000

The design of low-solidity vaned diffusers and the effect on the performance of a turbocharger compressor is discussed. The effect of vane number and turning angle was investigated while maintaining a basic design with a leading edge angle of $70^{\circ}$, leading and trailing edge radius ratios of 1.1 and 1.3. All results are compared with those obtained with the standard vaneless diffuser configuration and it was shown that all designs increased and shifted the pressure ratio to reduced flowrates. Despite the low-solidity configuration none of the vane designs provided a broad operating range, and the vane leading edge angle was not main factor that system went into the surge condition. The diffuser of higher trailing edge angle improved the flow range for the compressor to operate at lower flow region.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.767-770
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• 2002

The performance and noise characteristics of the design parameters of a cross-flow fan are investigated by computational methods. The incompressible Wavier-Stokes equations in moving coordinates are time-accurately solved for obtaining the pressure fluctuations due to the aerodynamic interactions between the impeller blades and the stabilizer, and sound pressure is then computed by the Ffowcs Williams-Hawkings equation. Design parameters of the cross-flow fan include blade setting angle, exit-diffusion angle, and stabilizer installation angle. Also, an optimization of the aforementioned design parameters has been peformed using the Taguchi method.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.218-224
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• 2011

A supersonic inlet at angle of attack has anti-symmetric pressure distribution, and it can make flow instability and structural problem. In this study, numerical analysis of three-dimensional inviscid flow was conducted under various throttle ratio and angle of attack conditions. Throttle ratio was defined as the ratio of the exit area to the smallest cross section area at inlet, and the ratio is controlled from 0 to 2.42. At various angle of attack, the characteristics of steady and unsteady flow around supersonic inlet is observed under different throttling ratios. From these results, pressure recovery curves and pressure history curves were plotted by post processing. Using pressure history data, FFT analysis is also carried out. Through these processes, it shows the tendency of pressure distribution anti-symmetricity and changing dominant frequency as increasing angle of attack.