• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.3
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• pp.963-969
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• 1991

본 연구에서는 누설와류는 유동에 영향을 미치며 에너지 손실로 된다. 누설 와류에 의한 손실은 다른 원인에 의한 손실에 비교하여 그 비중이 크다. 따라서 누 설와류 특성을 이해하기 위해 설계영각(.alpha.=10.7˚)에서 절현비를 t/C=0.90와 2.71로 바꾸고, 또 절현비가 설계절현비 t/C=0.90일 경우에 영각을 설계 영각 .alpha.=10.7˚와 실 속점의 영각 .alpha.=18.9˚사이에서 바꾸어 회전익 후방의 회전유동장을 측정하여 누설와 류의 거동을 연구하였다.

• Journal of Power System Engineering
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• v.16 no.1
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• pp.44-50
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• 2012

팁 간격의 크기가 냉각탑용 축류팬의 성능과 누설 유동에 미치는 영향을 조사하기 위해서 서로 다른 2가지 팁 간격을 가진 경우에 대해서 점성유동을 해석하였다. 케이싱 내에서 작동하는 축류팬 주위의 유동을 연속방정식, Navier-Stokes 방정식 등을 지배방정식으로 사용하여 수치해석 하였다. 난류유동에 나타나는 레이놀즈 응력은 ${\kappa}-{\epsilon}$ 난류모델을 사용하여 계산하였다. 전체적으로 H형 격자계를 사용하였으며, 팁 주위의 유동을 해석하기 위해서 팁 영역 주위에 부분적으로 조밀한 격자를 두었다. 팁 간격이 증가하면 누설 유동의 증가로 인한 유동 손실의 증가로 전압상승과 수력효율이 감소하였다. 팬 직경에 대한 팁 간격이 0.4%에서 1.0%로 증가하면 전압상승 값이 약 10% 정도 감소하였으며, 수력효율은 약 3% 정도 감소하였다. 팁 간격이 팁 근처 날개 주위의 압력에 미치는 영향을 보면, 팁 간격이 증가하여 누설 유동이 증가하면 흡입면과 압력면의 압력차가 전연 부근에서 감소함을 알 수 있었다. 누설 와류의 중심은 코드를 따라서 흡입면으로 부터 떨어져 나가면서 형성됨을 알 수 있었다. 누설 와류의 위치를 보면 팁 간격이 증가하면 와류 중심의 위치가 흡입면 쪽으로 이동하고, 흡입면에서 떨어진 거리도 날개 후반부에서 증가 폭이 커지는 포물선 형태로 증가함을 알 수 있었다.

• 유체기계공업학회:학술대회논문집
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• 1998.02a
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• pp.55-62
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• 1998

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.103-111
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• 2024

Axial-flow fans are used to transport fluids in relatively low-pressure flow regimes, and a variety of design variables are employed. The tip geometry of an axial fan plays a dominant role in its flow and noise performance, and two of the most prominent flow phenomena are the tip vortex and the tip leakage vortex that occur at the tip of the blade. Various studies have been conducted to control these three-dimensional flow structures, and winglet geometries have been developed in the aircraft field to suppress wingtip vortices and increase efficiency. In this study, a numerical and experimental study was conducted to analyze the effect of winglet geometry applied to an axial fan blade for an air conditioner outdoor unit. The unsteady Reynolds-Averaged Navier-Stokes (RANS) equation and the FfocwsWilliams and Hawkings (FW-H) equation were numerically solved based on computational fluid dynamics techniques to analyze the three-dimensional flow structure and flow noise numerically, and the validity of the numerical method was verified by comparison with experimental results. The differences in the formation of tip vortex and tip leakage vortex depending on the winglet geometry were compared through a three-dimensional flow field, and the resulting aerodynamic performance was quantitatively compared. In addition, the effect of winglet geometry on flow noise was evaluated by numerically simulating noise based on the predicted flow field. A prototype of the target fan model was built, and flow and noise experiments were conducted to evaluate the actual performance quantitatively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.9
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• pp.1106-1112
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• 1999

Substantial losses behind axial flow rotor are generated by the wake, various vortices in the hub region and the tip leakage vortex in the tip region. Particularly, the leakage vortex formed near blade tip is one of the main causes of the reduction of performance, generation of noise and aerodynamic vibration in downstream. In this study, the three-dimensional flow fields in an axial flow rotor were calculated with varying tip clearance under various flow rates, and the numerical results were compared with experimental ones. The numerical technique was based on SIMPLE algorithm using standard $k-{\varepsilon}$ model(WFM) and Launder & Sharma's Low Reynolds Number $k-{\varepsilon}$ model(LRN). Through calculations, the effects of tip clearance and attack angle on the 3-dimensional flow fileds behind a rotor and leakage flow/vortex were investigated. The presence of tip leakage vortex, loci of vortex center and its behavior behind the rotor for various tip clearances and attack angles was described well by calculation.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.845-850
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• 2003

Unsteady nature of a tip leakage vortex in an axial flow fan operating at a design and off-design operating conditions has been investigated by measuring the velocity fluctuation in a blade passage with a rotating hotwire probe sensor. Two hot-wire probe sensors rotating with the fan rotor were also introduced to obtain the cross-correlation coefficient between the two sensors located in the vortical flow as well as the fluctuating velocity. The results show that the vortical flow structure near the rotor tip can be clearly observed at the quasi-orthogonal planes to a tip leakage vortex. The leakage vortex is enlarged as the flow rate is decreased, thus resulting in the high blockage to main flow. The spectral peaks due to the fluctuating velocity near the rotor tip are mainly observed in the reverse flow region at higher flow rates than the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.227-233
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• 1999

Detailed Measurements were made to investigate the turbulence characteristics of a leakage vortex in an axial-flow fan using three-dimensional LDV. The turbulence in the leakage vortex has highly anisotropic characteristics with the radial value being the maximum. The turbulence intensity components in the vortex in the streamwise and tangential directions increase up to a certain downstrean position and then decrease. This increase is mainly due to the rapid decrease of the streamwise velocity of the vortex and partly due to the radial gradient of the streamwise velocity caused by a velocity deficit. As the vortex decays moving downstream, turbulence intensity also decrease gradually.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.404-411
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• 2003

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 Wavier-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.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.496-501
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• 2003

Reynolds averaged Wavier-Stokes simulations based on the Reynolds stress model was performed to investigated the effect of inlet flow angle on the distributions of the Reynolds stress tensor inside tip leakage vortex of a linear compressor cascade. Two different inlet flow angles ${\beta}=29.3^{\circ}$(design condition) and $36.5^{\circ}$(off-design condition) were considered. Stress tensor analysis, which transforms the Reynolds stress into the principal direction, was applied to show an anisotropy of the normal stresses. Whereas the anisotropy was highest in the region where the tip leakage vortex collides the suction side of the blade and tip leakage flow enters between blade tip of the pressure side and the endwall, it had the lowest value at the center of tip leakage vortex. It was also found that the magnitude of maximum shear stress at design condition was greater than that of off-design condition.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.244-249
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• 2002

It is known that tip clearance flows reduce the pressure rin, flow range and efficiency of the turbomachinery. So, the clear understanding about flow fields in the tip region is needed to efficiently design the turbomachinery. The Navier-Stokes code with the proper treatment of the boundary conditions has been developed to analyze the three-dimensional steady viscous flow fields in the transonic rotating blades and a numerical study has been conducted to investigate the detail flow physics in the tip region of transonic rotor, NASA Rotor 67. The computational results in the tip region of transonic rotors show the leakage vortices, leakage flow from pressure side to suction side and their interaction with a shock Depending on the operating conditions, the position of shock-wave on the blade surface are v8y different close to the blade tip of the transonic compressor rotor. The shock-wave position dose to the blade tip had the dose relationship with the starting position of leakage vortex and the direction of leakage flow.