• International Journal of Fluid Machinery and Systems
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• 제4권3호
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• pp.307-316
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• 2011

In order to clarify the features of tip leakage vortex near blade tip region in a half-ducted axial fan with large bellmouth, the experimental investigation was carried out using a 2-dimensional LDV system. Three sizes of tip clearance (TC) were tested: those sizes were 1mm (0.55% of blade chord length at blade tip), 2mm (1.11% of blade chord length at blade tip) and 4mm (2.22% of blade chord length at blade tip), and those were shown as TC=1mm, TC=2mm and TC=4mm, respectively. Fan characteristic tests and the velocity field measurements were done for each TC. Pressure - flow-rate characteristics and two-dimensional velocity vector maps were shown. The vortex trace and the vortex intensity distribution were also illustrated. As a result, a large difference on the pressure - flow-rate characteristics did not exist for three tip clearance sizes. In case of TC=4mm, the tip leakage vortex was outflow to downstream of rotor was not confirmed at the small and reference flow-rate conditions. Only at the large flow-rate condition, its outflow to downstream of rotor existed. In case of TC=2mm, overall vortex behaviors were almost the same ones in case of TC=4mm. However, the vortex trace inclined toward more tangential direction. In case of TC=1mm, the clear vortex was not observed for all flow-rate conditions.

• 대한기계학회논문집B
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• 제37권7호
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• pp.709-716
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• 2013

팬 필터 유닛 (FFU)은 청정실 천정에 설치되어 정화된 공기를 공급하는 장치이다. FFU가 대형화되면서 출구면에서 속도가 불균일해지고 결과적으로 청정실에서 생산되는 제품의 품질 또는 생산성을 떨어뜨리게 된다. 이러한 문제를 해결하기 위해 가이드 베인이 설치되는데 가이드 베인은 속도를 균일하게 하지만 유동저항을 유발하여 동력이 일정하게 주어진 경우 공급되는 유량을 감소시킨다. 따라서 속도 균일성을 확보하면서 유량 감소를 최소화하는 최적설계가 요구된다. 본 연구에서는 FFU의 외벽과 중앙에 설치된 가이드 베인의 각도와 길이를 변경하면서 수치해석을 수행하여 가이드 베인의 성능 개선 방안을 도출하였다. 외벽에 설치된 가이드 베인의 경우, 형상을 변경하여 유량이 1.5% 감소하는 조건에서 속도 균일도를 3.7% 향상시킬 수 있었다. 중앙 가이드 베인의 경우 유량이 0.7% 감소하는 조건에서 속도 균일도를 2.9% 향상시킬 수 있었다.

• 설비공학논문집
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• 제14권7호
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• pp.567-574
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• 2002

In the present study, ventilation flow rates and pressure rises through a road tunnel are simulated numerically using CFD with the various conditions such as roughness height, swirl angle of jet fan, entrance and exit effect and hub to tip ratio. By using a modified wall function, friction factor can be predicted under 10％ of error with respect to the Moody chart for the circular pipe flow and 15％, for the present tunnel. For more precise design, the effects of the swirl angle and hub to tip ratio of jet fan, which is not included in the theoretical equation of pressure rise by jet fan are necessary to be considered.

• 설비공학논문집
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• 제19권5호
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• pp.386-393
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• 2007

This paper studies the ventilation characteristics according to the jet fan location at the long road tunnel using the CFD software 'FLUENT' which is based on the finite volume method. The tunnel model used in the analysis has a length of 1600m, a cross sectional area of $120m^3$, and is composed of 3 lanes and one way. The velocity profile, the distribution of CO concentration and the ventilation flow rate within the tunnel are analyzed, respectively. In the analysis, it is found that the dependence of the ventilation flow rate upon the jet fan location is small, but the CO concentration in the tunnel is at the lowest when the jet fans are installed near the tunnel outlet. An air stream right below the jet fan is almost inactive due to the strong stream injection near the jet fan. Thus, the pollution level below the jet fan must be higher than the other area.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.123-128
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• 2002

Over the range(OTR) has been applied for cooking and ventilation functions especially in northern Amarica. Because flow rate and operating rpm of the double sided sirocco fan for ventilation are much higher and than the microwave oven system, the major noise source is the sirocco fm. Recently, the quiet fan development is one of very important issues for amenity. In this study, the noise source identification using multi-microphone array system was carefully carried out and numerical simulations for understanding the aerodynamic and aeroacoustic of the fan were peformed. The sound level of tonal noise is predicted with a good accuracy but that of the broadband shows some discrepancy. In order to reduce the broadband noise, the inlet region of sirocco fan have to be modified that the secondary flow should be suppressed. Based on these results, new low noise fan and OTR is now developing.

• 대한기계학회논문집B
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• 제28권2호
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• pp.181-188
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• 2004

The frequency characteristics in an axial flow fan operating at a design and three off-design operating conditions have been investigated by measuring the velocity fluctuation of a tip leakage vortex and a wake flow. Two hot-wire probe sensors rotating with the fan rotor. a fixed and a moving ones, were introduced to obtain a cross-correlation coefficient between two sensors as well as the fluctuating velocity. The results show that the spectral peaks due to the fluctuating velocity near the rotor tip are mainly observed in the reverse flow region of higher flow rates than those in the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition. Detailed wake flow just downstream of the rotor blade was also measured by the rotating hot-wire sensor. The peak frequency of a high velocity fluctuation due to Karman vortex shedding in the wake region is mainly observed at the higher flow rate condition than that in the design point.

• 한국유체기계학회 논문집
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• 제7권1호
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• pp.36-44
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• 2004

Three-dimensional vortical flow and separated flow topology near the casing wall in an axial flow fan having two different tip clearances have been investigated by a Reynolds-averaged Navier-Stokes (RANS) flow simulation. The simulation shows that the tip leakage vortex formed close to the leading edge of the blade tip on suction side grows in the streamwise direction. On the casing wall, a separation line is formed upstream of the leakage vortex center due to the interference between the leakage vortex and main flow. The reverse flow is observed between the separation line and the attachment line generated downstream of the trailing edge, and increased with enlarging tip clearance. The patterns of a leakage velocity vector including a leakage flow rate are also analyzed according to two tip clearances. It is noted that the understanding of the distribution of a limiting streamline on the casing wall is very important to grasp the characteristics of the vortical flow in the axial flow fan.

• 대한기계학회논문집B
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• 제24권10호
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• pp.1335-1342
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• 2000

Three-dimensional flow analysis and numerical optimization methods are presented for the design of an axial-flow fan. Steady, incompressible, three-dimensional Reynolds-averaged Navier-Stokes equations are used as governing equations, and standard k- ${\varepsilon}$ turbulence model is chosen as a turbulence model. Governing equations are discretized using finite volume method. Steepest descent method, conjugate gradient method and BFGS method are compared to determine the searching directions. Golden section method and quadratic fit-sectioning method are tested for one dimensional search. Objective function is defined as a ratio of generation rate of the turbulent kinetic energy to pressure head. Two variables concerning sweep angle distribution are selected as the design variables. Performance of the final fan designed by the optimization was tested experimentally.

• 한국유체기계학회 논문집
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• 제4권2호
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• pp.7-14
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• 2001

Design and development of a propeller fan for a cooling tower have been accomplished by both numerical prediction of performance and experimental validation with a wind tunnel. Main interest lies on blade geometry of a fan for optimal design of aerodynamic performance. A commercial program, Fine/Turbo used for the present numerical estimation, gives us engineering information such as flow details near the blades and flow rate of the system. The numerical results are compared with precise experimental output and show good agreement in comparison between the two data. Also new proposed model of a blade shows improved performance relative to present running model in market.

• 한국유체기계학회 논문집
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• 제7권4호
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• pp.7-15
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• 2004

The design point of the cross-flow fan is generally based on the region within low static pressure and high flow rate. It relatively makes high dynamic pressure at low speed because a working fluid passes through an impeller blade twice. However, it has low static pressure efficiency between $30\%$ and $40\%$ because of relative high impact loss. The purpose of this study is to research the reciprocal relation among each parameter. Experiments and numerical analyses are conducted on effects of a stabilizer and a rearguider on performance analysis of a cross-flow fan. Two-dimensional, unsteady governing equations are solved using FVM, PISO algorithm, sliding grid system and standard $k-{\epsilon}$ turbulence model. Experiments are also carried out to estimate the performance of the modeled cross-flow fan. It is clarified that the rearguider of Archimedes type has excellent results for the most part.