• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.822-827
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• 2003

Experiments were done for the three dimensional unsteady flow in a counter rotating axial flow fan under stable operating condition. Flow fields in a counter rotating axial flow fan were measured at cross-sectional planes of the upstream and downstream of each rotor. Cross sectional flow patterns were investigated through the acquired data by the $45^{\circ}$ inclined hot-wire. Flow characteristics such as tip vortex, secondary flow and tip leakage flow were confirmed through axial, radial and tangential velocity vector plot. Swirl velocity, which was generated by the front rotor, was recovered in the form of static pressure rise by the rear rotor except for hub and tip regions.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.160-163
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• 2010

부분흡입형 초음속 터빈의 노즐과 1단 로터 사이의 축방향 간극이 터빈의 단 성능과 유동장에 어떤 영향을 미치는지 알아보기 위해 터빈에 대한 3차원 유동해석을 수행하고 그 결과를 분석하였다. 상용 유동해석 프로그램 $FLUENT^{TM}$를 사용하였으며 다섯 가지 경우의 축간극에 대해 계산을 하였다. 노즐-로터 축간극이 팁 누설 유량의 증가와 로터 출구의 유동각에 영향을 주는 것을 확인하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권3호
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• pp.219-227
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• 2016

Numerical simulation based on the Reynolds Averaged Naviere-Stokes (RANS) Computational Fluid Dynamics (CFD) method had been carried out with the commercial code ANSYS CFX. The structured grid and SST $k-{\omega}$ turbulence model had been adopted. The impact of non-condensable gas (NCG) on cavitation performance had been introduced into the Schnerr and Sauer cavitation model. The numerical investigation of cavitating flow of marine propeller E779A was carried out with different advance ratios and cavitation numbers to verify the numerical simulation method. Tip clearance effects on the performance of pumpjet propulsor had been investigated. Results showed that the structure and characteristics of the tip leakage vortex and the efficiency of the propulsor dropped more sharply with the increase of the tip clearance size. Furthermore, the numerical simulation of tip clearance cavitation of pumpjet propulsor had been presented with different rotational speed and tip clearance size. The mechanism of tip clearance cavitation causing a further loss of the efficiency had been studied. The influence of rotational speed and tip clearance size on tip clearance cavitation had been investigated.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.305-310
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• 2007

엇회전식 축류팬의 복잡한 유동특성을 이해하고 설계, 공력 해석 및 소음 특성 예측에 활용될 수 있는 3차원 비정상 유동장을 측정하였다. 엇회전식 축류팬의 3차원 비정상 유동장은 작동 영역인 설계점에서 $45^{\circ}$ 경사 열선을 이용하여 전단 동익의 전방, 전단 동익과 후단 동익 사이 그리고 후단 동익의 후방의 수직 유로 단면에서 측정되었다. 엇회전식 축류팬의 전단 동익과 후단 동익에 의해 발생되는 후류, 팁 와류 및 팁 누설 유동의 비정상 특성을 속도 벡터와 속도 윤곽을 통해 나타내었다.

• 대한기계학회논문집B
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• 제29권8호
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• pp.956-962
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• 2005

A three-dimensional computation was conducted to make a study about effects of the inlet boundary layer thickness on the total pressure loss in a low-speed axial compressor operating at the design condition ($\phi=85\%$) and near stall condition($\phi=65\%$). Differences of the tip leakage flow and hub corner-stall induced by the inlet boundary layer thickness enable the loss distribution of total pressure along the span to be altered. At design condition, total pressure losses for two different inlet boundary layers are almost alike in the core flow region but the larger loss is generated at both hub and tip when the inlet boundary layer is thin. At the near stall condition, however, total pressure loss fer the thick inlet boundary layer is found to be greater than that for the thin inlet boundary layer on most of the span except the region near hub and casing. Total pressure loss is scrutinized through three major loss categories in a subsonic axial compressor such as profile loss, tip leakage loss and endwall loss using Denton's loss model, and effects of the inlet boundary layer thickness on the loss structure are analyzed in detail.

• 한국유체기계학회 논문집
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• 제14권1호
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• pp.48-54
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• 2011

The effect of channel cutback on three-dimensional flow fields and aerodynamic losses downstream of a cavity squealer tip has been investigated in a turbine rotor cascade for the squealer rim height-to-chord ratio and tip gap height-to-chord ratio of $h_{st}/c$ = 5.51% and h/c = 2.0% respectively. The cutback length-to-camber ratio is changed to be $CB/c_c$ = 0.0, 0.1, 0.2 and 0.3. The results show that longer cutback delivers not only stronger secondary flow but also higher aerodynamic loss in the tip leakage vortex region, meanwhile it leads to lower aerodynamic loss in the passage vortex region. The discharge of cavity fluid through the cutback opening provides a beneficial effect in the reduction of aerodynamic loss, whereas there also exists a side effect of aerodynamic loss increase due to local wider tip gap near the trailing edge. With increasing $CB/c_c$ from 0.0 to 0.3, the aerodynamic loss coefficient mass-averaged all over the measurement plane tends to increase slightly.

• 한국유체기계학회 논문집
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• 제15권6호
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• pp.5-10
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• 2012

The effect of pressure-side opening length on three-dimensional flow fields and aerodynamic losses downstream of a cavity squealer tip has been investigated in a turbine rotor cascade for the squealer rim height-to-chord ratio and tip gap height-tochord ratio of $h_{st}/c$ = 5.05% and h/c = 2.0% respectively. The opening length-to-camber ratio is changed to be $OL/c_c$ = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7 The results show that longer OL leads not only to weaker secondary flow but also to lower aerodynamic loss in the tip leakage vortex region, while it significantly widens the area with high aerodynamic loss in the passage vortex region. The aerodynamic loss coefficient mass-averaged all over the measurement plane is kept almost constant for $0.0{\leq}OL/c_c{\leq}0.3$, whereas it increases rapidly for $OL/c_c$ > 0.3 in proportion to $OL/c_c$. There is little deterioration in flow turning with increasing $OL/c_c$.

• 대한기계학회논문집B
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• 제30권4호
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• pp.328-336
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• 2006

Detailed heat transfer coefficient distributions an two. types of gas turbine blade tip, plane tip and squealer tip, were measured using a hue-detection base transient liquid crystals technique.. The heat transfer coefficients an the shroud and near tip regions of the pressure and suction sides af the blade were also. measured. The heat transfer measurements were taken at the three different tip gap clearances af 1.0%, 1.5%, and 2.5% of blade span. Results shaw the overall heat transfer coefficients on the tip and shroud with squealer tip blade were lower than those with plane tip blade. By using squealer tip, however, the reductions af heat transfer coefficients near the tip regions of the pressure and suction sides were nat remarkable.

• International Journal of Aeronautical and Space Sciences
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• 제16권2호
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• pp.157-164
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• 2015

The present work performs three-dimensional flow calculations based on Reynolds Averaged Navier-Stokes (RANS) and Delayed Detached Eddy Simulation (DDES) to investigate the flow field of a transonic rotor (NASA Rotor 37) at near-stall condition. It is found that the DES approach is likely to predict well the complex flow characteristics such as secondary vortex or turbulent flow phenomenon than RANS approach, which is useful to describe the flow mechanism of a transonic compressor. Especially, the DES results show improvement of predicting the flow field in the wake region and the model captures reasonably well separated regions compared to the RANS model. Besides, it is discovered that the three-dimensional vortical flows after the vortex breakdown from the rotor tip region are widely distributed and its vortex structures are clearly present. Near the rotor leading edge, a part of the tip leakage flows in DES solution spill over into next passage of the blade owing to the separation vortex flow and the backflow is clearly seen around the trailing edge of rotor tip. Furthermore, the DES solution shows strong turbulent eddies especially in the rotor hub, rotor tip section and the downstream of rotor trailing edge compared to the RANS solution.

• Tribology and Lubricants
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• 제39권2호
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• pp.61-71
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• 2023

This study proposes a procedure for designing a labyrinth seal that meets both leakage flow rate and rotordynamic performance criteria (effective damping, amplification factor, separation margin, logarithmic decrement, and vibration amplitude). The seal is modeled using a one control volume (1CV) bulk flow approach to predict the leakage flow rate and rotordynamic coefficients. The rotating shaft is modeled with the finite element (FE) method and is assumed to be supported by two linearized bearings. Geometry, material and operating conditions of the rotating shaft, and the supporting characteristics of the bearings were fixed. A single labyrinth seal is placed at the center of the rotor, and the linearized dynamic coefficients predicted by the seal numerical model are inserted as linear springs and dampers at the seal position. Seal designs that satisfy both leakage and rotordynamic performance are searched by modifying five seal design parameters using the multi-grid method. The five design parameters include pre-swirl ratio, number of teeth, tooth pitch, tooth height and tooth tip width. In total, 12500 seal models are examined and the optimal seal design is selected. Finally, normalization was performed to select the optimal labyrinth seal designs that satisfy the system performance requirements.