• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.25-30
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• 2014

The flow characteristics of two types of overhung compressor volutes for automobile turbochargers were analyzed numerically using commercial software. For obtaining high performance from a volute, it is necessary that the volute have a high pressure recovery coefficient and a low loss coefficient. We investigated the flow characteristics of two types of overhung compressor volutes with a fixed diffuser inlet angle of $24^{\circ}$ and a mass flow rate of 0.055 kg/s. The first type is a volute with one-arc cross section (type 1) and the second type is with three-arc cross section (type 2). Our results showed that between the two types of volutes, type 2 had the higher pressure recovery coefficient and the lower loss coefficient along the entire angular position.

• Nuclear Engineering and Technology
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• v.27 no.4
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• pp.491-502
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• 1995

In accurate prediction of cross-flow based on detailed knowledge of the velocity field in subchannels of a nuclear fuel assembly is of importance in nuclear fuel performance analysis. In this study, the low-Reynolds number k-$\varepsilon$ turbulence model has been adopted in too adjacent subchannels with cross-flow. The secondary flow is accurately estimated by the anisotropic algebraic Reynolds stress model. This model was numerically calculated by the finite element method and has been verified successfully through comparison with existing experimental data. Finally, with the numerical analysis of the velocity Held in such subchannel domain, an analytical correlation of the lateral loss coefficient is obtained to predict the cross-flow rate in subchannel analysis codes. The correlation is expressed as a function of the ratio of the lateral How velocity to the donor subchannel axial velocity, recipient channel Reynolds number and pitch-to-diameter.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.5
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• pp.548-556
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• 2013

A tapered production tubing with two different inner diameters has been suggested to increase production rates. In this research, various tapered tubing combinations are taken into account and possible tubing combinations are proposed to satisfy each objective. In previous studies, production enhancement was the main goal. However, this research also considers flow stability by analyzing tubing pressure traverse, liquid holdup, and operating conditions. For a reservoir assumed in this research, a tapered tubing of, 4.5 inch inner diameter(ID) and 2000 ft in length in the lower part and 5.5 inch ID and 8000 ft in the upper part, shows the highest net present value. Compared to a mono tubing, tapered tubings enable various tubing designs because they have smaller differences in frictional pressure loss. It is important to maintain low liquid holdup to prevent liquid loading. Smaller ID of tapered tubing in the lower part enables to achieve the object. In conclusion, it is identified that various tubing designs are achievable from the analyses of overall production operations depending on purposes specified.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.4
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• pp.81-89
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• 2014

Tandem-ejector has been devised for engine-bay cooling. In this study, 1-D model has been developed to analyze Tandem-ejector. In the model, the primary, the secondary and the tertiary flow conditions have been analyzed with isentropic process. The mixing process has been analyzed with conservation laws based on the control volume analysis. The total pressure loss of the primary flow has been analyzed under the matching condition between the static pressure of Tandem-ejector discharge flow and atmospheric pressure. Consequently, 1-D model can predict Tandem-ejector performance accurately and provide the performance map.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.301-307
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• 2012

The characteristics of pressure loss in an asymmetric bifurcating tube were investigated numerically for steady inspiratory conditions. The loss coefficient K calculated for various asymmetry and flow-distribution ratios found in human lung airways showed a power-law dependence on the Reynolds number (Re) and length-to-diameter ratio (L/d), with different exponents for Re $\geq$ 100 and Re < 100. The fundamental characteristics of the asymmetric bifurcation are similar to the case of symmetric bifurcation. In addition, the effect of skewed inlet velocity profiles on the pressure loss was weak, and decreased with an increasing number of bifurcations.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.631-636
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• 2001

The internal flow in the rocket pump inducer of LE-7 engine for H-II rocket was predicted at design and off-design flow rates using CFD code, CFX- Tascflow. In this numerical study, the performance curve of inducer coressponding to flow rates variation and the internal flow in the front of blade leading edge show good agreement between the calculations and the measurements. Backflow is appeared at suction side of leadinge edge tip, and this region is extended to upstream as flowrate decrease. Because of backflow, pressure loss coressponding to meridinal coordinate occupy 50% from inlet domain to leading edge. By this phenomena, pressure loss in front of blade leading edge take a great effect to inducer performance.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.243-249
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• 2001

Steady state flow calculations are executed for turbo-pump inducers of modem design to validate the performance of Tascflow code. Hydrodynamic performance is evaluated and structure of the passage flow and leading edge recirculation are also investigated. Calculated results show good coincidence with experimental data of static pressure performance and velocity profiles over the leading edge. Upstream recirculation, tip leakage and vortex flow at the blade tip and near leading edge are main source of pressure loss. Amount of pressure loss from the upstream to the leading edge corresponds to that of pressure loss through the whole blade. The total viscous loss is considerably large due to the strong secondary flow.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1979-1989
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• 1992

An experimental study has been performed to investigate the horseshoe vortex system formed around cylindrical obstacles mounted vertically on the surface over which a boundary layer is formed. To measure the mean velocity of the flow field, a five-hole Pitot tube has been used. In addition, surface static pressure measurements and surface flow visualization were also performed. From the five-hole probe measurements, vorticity distribution was deduced numerically and the streamwise velocity distribution was also examined. To consider the effect of the leading-edge shape on the formation of the horseshoe vortex, a qualitative comparison was made between the three-dimensional flows around a circular cylinder and a wedge-type cylinder. The five-hole probe measurements showed a single primary vortex which exists immediately upstream of the obstacles, and endwall flow visualization showed the existence of a corner vortex. As the vortex passes around the obstacle, the vortex strength is reduced and the vortex core moves radially outward. Due to this horseshoe vortex, the fluid momentum is found to decrease along the streamwise direction. Since the horseshoe vortex formed around a wedge-type cylinder has weaker strength and is confined to a narrower region than that around a circular, the possibility that the secondary flow loss due to the horseshoe vortex can be reduced through a change of the leading- edge shape is proposed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.21-29
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• 2002

In the present study, a passive control method, using a porous wall and cavity system, is applied to the shock wave/boundary layer interactions in transonic moist air flow. The two-dimensional, unsteady, compressible, Navier-Stokes equations, which are fully coupled with a droplet growth equation, are solved by the third-order MUSCL type TVD finite difference scheme. Baldwin-Lomax model is employed to close the governing equations. In order to investigate the effectiveness of the present control method, the total pressure loss of the flow and the time-dependent behaviour of shock motions are analyzed in detail. The computed results show that the present passive control method considerably reduces the total pressure losses due to the shock wave/boundary layer interaction in transonic moist air flow and suppresses the unsteady shock wave motions over the airfoil as well. It is also found that the location of the porous ventilation significantly affects the control effectiveness.

• 월간 기계설비
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• s.35
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• pp.84-96
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• 1993

본 연구는 '초고층 아파트 최적 설비시스템 개발'의 제2차년도 연구로서 아직까지 국내에서 확립되어 있지 않은 초고층 아파트 급수설비 시스템 및 수격방지 시스템의 모델정립과 연돌효과에 의한 열손실 추정 및 적정 설계 지침 설정에 관한 연구를 수행하였다. 이를 위하여 이론 해석 및 현장실험을 수행하였고, 결과분석을 통하여 최적화 설계방안도 아울러 도출하였다. 급수설비 분야에서는 각종 급수 시스템의 해석 및 비교를 통한 효율적인 시스템의 설계 및 선정방법을 제시 하였고, 실제 초고층 아파트에 대한 수격현상 해석 및 실험을 통하여 수격작용의 영향을 감소시킬 수 있는 설계방안을 검토하였다. 또 입주중인 초고층 아파트 현장에서의 실측을 통하여 건물의 높이에 따라 불균일한 틈새가 있는 일반적인 경우에 대한 모델을 정립하였고, 수치해석을 통한 수직통로 내의 실제 열유동 현상을 정량화하고 설계지침을 제시하였다. 결과로서 각종 급수시스템의 해석을 위한 프로그램을 개발하였고, 수격의 발생을 억제하기 위한 최적 밸브 폐쇄형태를 제시하였으며, 초고층 건물의 내외부에 형성되는 압력차와 유인풍량 및 열손실량 사이의 관계식을 얻었다.