• 대한기계학회논문집B
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• 제20권10호
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• pp.3262-3271
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• 1996

Flow patterns were measured in a shrouded centrifugal impeller. The flow rate in measurements was fixed at the value corresponding to a nearly zero incidence at the blade inlet. By using a single slanted hot-wire probe and a Kiel probe mounted on the impeller hub disk, the 3-D relative velocities and the rotary stagnation pressures were measured in seven circumferential planes from the inlet to the outlet of impeller rotating at 700 rpm, and the static pressure distribution along flow passage and the slip factor at impeller outlet were calculated from the measured values. From these measured data, the primary and secondary flows, the wake production and the static pressure rise in the impeller passage were investigated. Furthermore, the secondary flow patterns and the wake's location in this impeller passage were compared with those of the unshrouded impeller.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.163-166
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• 2003

Maintaining low temperature is very important in operating HTS cable termination in which Joule heat is generated at current lead. In this study, numerical analysis using FLUENT is performed to find an optimized flow conditions for effective cooling of HTS cable terminal system using subcooled liquid nitrogen (L$N_2$) as refrigerant. The variables considered here are mass flow rate of L$N_2$, location of inlet and diameter of inlet and outlet. Simplified models are investigated under these variables. Based on maximum temperatures in the cryostat, the configuration for effective cooling of HTS cable was determined.

• 설비공학논문집
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• 제19권9호
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• pp.662-668
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• 2007

In this study, jet fans are installed with 4 cases in the straight long tunnel; inlet-side setup, middle-side setup, outlet-side setup, and dispersion setup. A bus is selected as fired car, of which fire size is 20MW. And fired car locates at 100m, 700m, 1500m position from tunnel inlet, respectively. FLUENT, commercial finite-volume code, is used to analyze the performance. The velocity profile, $CO_2$ concentration, temperature distribution are examined for analysis. Performance of smoke control is compared by the backlayering length. Consequently, inlet-side setup of jet fans is a little more efficient than other cases considering the fire occurrence frequency in tunnel.

• 한국환경농학회지
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• 제27권2호
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• pp.150-155
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• 2008

본 연구는 입기구가 11개이고 배기구가 9개인 무창이유자돈사에 대하여 CFD 시뮬레이션을 실시함으로써 겨울철 최적 환기를 위한 입 배기구의 위치와 개수 및 최적 공기 유입속도를 구명하고자 수행되었다. 배기팬에 가까운 돈방의 경우에는 나머지 돈방에 비해 상대적으로 음압이 크기 때문에 환기가 많이 되는 것으로 나타났고, 나머지 돈방의 경우에는 음압이 작아 환기가 적게 되는 것으로 나타났다. 이런 이유로 동일 면적의 입기구를 설치함에 있어서 같은 간격으로 배치하면 환기가 불균일하게 이루어지기 때문에, 배기팬에 가깝게 위치한 돈방에서는 입 배기구를 나머지 돈방에 비해 적게 만들어 주거나 간격을 넓게 만들어 줌으로써 균일한 환기를 할 수 있는 것으로 분석되었다. 특히 입기구가 11개이고 배기구가 9개인 무창돈사의 경우에는 동일 선상에 있는 입기구 4개를 폐쇄하며 배기구 1개는 완전 폐쇄하고 2개는 2/3를 폐쇄하였을 때 환기가 균일하게 되는 것으로 나타났다. 또한 실험돈사와 같이 돈사의 폭이 3 m 정도일 경우에는 입기구의 입공기 속도가 0.5 $m\;sec^{-1}$ 정도로 유지될 때 틈바닥 위 0.1 m 높이 위치의 풍속이 적정수준으로 유지되는 것으로 나타났다.

• 한국자동차공학회논문집
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• 제5권6호
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• pp.128-140
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• 1997

A new super compact condenser(SCC), which has been developed recently is especially suitable for an alternative refrigerant HFC-134a due to its high performance and compactness. The SCC is composed of two pipe headers, baffles, narrow multi-rectangular channels, and louvered fin arrays. Alternating inlet and outlet by the inserted baffles in pipe headers guide refrigerant to and from the narrow multi-rectangular channels. Since the flow rate and its lengh are changed depending on the number and location of baffles, the corresponding pressure drop and heat transfer rate are changed. The present study aims to theoretically and experimentally investigate the effects of baffle location and its number on the pressure drop and thermal performance of the SCC with 40 multi-rectangular channels. The results show that the present method provides an acceptable prediction of pressure drop and heat transfer rate for a 4 pass SCC. However, the model significantly under predicts the performance of a 3 pass SCC, which may be attributed to the phase separation of refrigerant flowing through header pipes. Pressure drop is more signifi- cantly influenced than heat transfer rate by the baffle location.

• International Journal of Fluid Machinery and Systems
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• 제6권4호
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• pp.200-205
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• 2013

In order to investigate the characteristics of unsteady flow in a mixed flow pump guide vane under the small flow conditions, several indicator points in a mixed flow pump guide vane was set, the three-dimensional unsteady turbulence numerical value of the mixed flow pump which is in the whole flow field will be calculated by means of the large eddy simulation (LES), sub-grid scale model and sliding mesh technology. The experimental results suggest that the large eddy simulation can estimate the positive slope characteristic of head & capacity curve. And the calculation results show that the pressure fluctuation coefficients of the middle section in guide vane inlet will decrease firstly and then increase. In guide vane outlet, the pressure fluctuation coefficients of section will be approximately axially symmetrical distribution. The pressure fluctuation minimum of section in guide vane inlet is above the middle location of the guide vane suction surface, and the pressure fluctuation minimum of section in which located the middle and outlet of guide vane. When it is under the small flow operating condition, the eddy scale of guide vane is larger, and the pressure fluctuation of the channel in guide vane being cyclical fluctuations obviously which leads to the area of eddy expanding to the whole channel from the suction side. The middle of the guide vane suction surface of the minimum amplitude pressure fluctuation to which the vortex core of eddy scale whose direction of fluid's rotation is the same to impeller in the guide vane adhere.

• 대한조선학회논문집
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• 제47권4호
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• pp.553-564
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• 2010

This paper studies on the rudder shapes for the suppression of the cavitation around a horn-type rudder. To improve the problems due to cavitation, there have been several studies. However, these some studies are recognized as incomplete ways to suppress the rudder cavitation. In this study, the section shapes to suppress the cavitation phenomena are determined by moving the location of maximum thickness for reducing the curvature variation and changing the radius of leading edge. Also, in the pintle part, the curvature radius of the inlet outlet edge of rudder plate is changed. During the design of rudder shape, two-dimensional numerical simulations are firstly performed because those offer some advantages with that cavitation phenomena becomes predictable for a short time, and then the three-dimensional numerical simulations are performed to confirm the determination. The time mean distribution of the propeller slipstream is imposed on the inlet boundary condition. As some results, this paper shows the effects reducing the range of the occurrence of cavitation, and suggests the references on the design of a horn-type rudder for the suppression of cavitation phenomena.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1999년도 학술발표대회 논문집 제18권 2호
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• pp.397-400
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• 1999

본 연구에서는 기존의 모드적합법의 단점을 개선하여 각 관에 임의의 모드갯수를 선택할 수 있고, 동심관형 단순확장관의 음향특성뿐만 아니라 입$\cdot$출구가 임의의 위치에 있는 경우에도 모드적합법을 적용할 수 있는 방안을 제시한다. 그리고 제시한 방안으로 프로그램을 작성하여, 각각 임의의 모드와 임의의 입$\cdot$출구의 위치를 가지는 원형 소음기의 4단자 정수를 구하고, 이로부터 임의의 입$\cdot$출구 위치에 따른 소음기의 음향특성을 구하여 유한요소법과 비교하여 제안하는 방법의 유용성을 검증하고 고차모드의 영향을 조사하였다.

• 대한기계학회논문집B
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• 제28권3호
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• pp.296-303
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• 2004

The heat and flow characteristics in a single-phase parallel-flow heat exchanger was examined numerically to obtain its optimal shape. A response surface method was introduced to approximately predict its performance with respect to the design parameters over the design domain. The inflow/outflow angle of the working fluid, the location of inlet/outlet, the protruding height of flat tube and the height of header were chosen as a design parameter The evaluation of the relative importance of the design parameters was performed based on a sensitivity analysis. An efficiency index was used as an evaluation characteristics value to simultaneously consider both the heat transfer and the pressure drop. The efficiency index of the optimum model, compared to that of the base model, was increased by 9.3%.

• 한국자동차공학회논문집
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• 제8권4호
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• pp.93-99
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• 2000

It is well known that an automotive muffle strongly influences engine efficiency and noise reduction. The performance of a muffler system is determined by the geometrical parameters such as the relative location of an inlet and outlet pipe size and cross sectional geometry of a chamber. In this study numerical analysis was performed to examine the flow characteristics in the simple automotive muffler for the variation of volumetric rate and offset. The computational grid generation was carried out. The RNG k-$\varepsilon$ turbulence model was applied. To provide the boundary condition for numerical analysis the experimental measurement wes carried out. As a result of this study we could understand that there was a recirculation flow inside muffler and pressure loss depends on the variation of volumetric rate and offset.