• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.8 s.227
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• pp.902-909
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• 2004

A steady-state Reynolds averaged Navier-Stokes simulation was conducted to investigate the distribution 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) at a constant tip clearance size of $1\%$ blade span were considered. Classical methods of solid mechanics, applied to view the Reynolds stress tensor in the principal direction system, clearly showed that the high anisotropic feature of turbulent flow field was dominant at the outer part of tip leakage vortex near the suction side of the blade and endwall flow separation region, whereas a nearly isotropic turbulence was found at the center of tip leakage vortex. There was no significant difference in the anisotropy of the Reynolds normal stresses inside tip leakage vortex between the design and off-design condition.

• The KSFM Journal of Fluid Machinery
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• v.7 no.6 s.27
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• pp.38-44
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• 2004

In this study, the overall performance and the effect of the tip leakage flow of the centrifugal compressor with a refrigerant HFC-l34a were numerically studied using CFX-TASCflow. To study the effect of the tip leakage flow, the numerical study of the overall performance of HFC-l34a centrifugal compressor with a cascade diffuser was preceded and compared with the experimental result. Six different tip clearances were used to consider the influence of the tip clearance on the performance. The tip leakage flow was illustrated for qualitative discussion. The results obtained in this study can be applied to the determination of the cold clearance.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.451-456
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• 2003

In this study, the overall performance and the effect of the tip leakage flow of the centrifugal compressor with the refrigerant HFC-l34a were numerically studied using CFX-TASCflow. To study the effect of a tip leakage flow, the numerical study of the overall performance of HFC-l34a centrifugal compressor with a cascade diffuser was preceded and compared with experimental result. Six different tip clearances were used to consider the influence of a tip clearance on performance. The tip leakage flow was illustrated for qualitative discussion. The results obtained in this study can be applied to the determination of the cold clearance.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2162-2167
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• 2003

It is well-known that high anisotropic characteristic of turbulent flow field is dominant inside tip leakage vortex. This anisotropic nature of turbulence invalidates the use of the conventional isotropic eddy viscosity turbulence model based on the Boussinesq assumption. In this study, to check whether an anisotropic turbulence model is superior to the isotropic ones or not, the results obtained from steady-state Reynolds averaged Navier-Stokes simulations based on the RNG ${\kappa}-{\varepsilon}$ and the Reynolds stress model in two test cases, such as a linear compressor cascade and a forward-swept axial-flow fan, are compared with experimental data. Through the comparative study of turbulence models, it is clearly shown that the Reynolds stress model, which can express the production term and body-force term induced by system rotation without any modeling, should be used to predict the complex tip leakage flow, including the locus of tip leakage vortex center, quantitatively.

• International Journal of Air-Conditioning and Refrigeration
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• v.12 no.1
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• pp.50-60
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• 2004

An experimental analysis using three-dimensional Laser Doppler Velocimetry(LDV) measurement and computational analysis using the Reynolds stress model in FLUENT are conducted to give a clear understanding of the effect of blade loading on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition ($\Phi$=0.25) and two off-design conditions ($\Phi$=0.21 and 0.30). As the blade loading increases, the onset position of the rolling-up of tip leakage flow moves upstream and the trajectory of tip leakage vortex center is more inclined toward the circumferential direction. Because the casing boundary layer becomes thicker and the mixing between the through-flow and the leakage jet with the different flow direction is enforced, the streamwise vorticity decays more fast with the blade loading increasing. A distinct tip leakage vortex is observed downstream of the blade trailing edge at $\Phi$=0.30, but it is not observed at $\Phi$=0.21 and 0.25.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.4
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• pp.294-304
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• 2003

An experimental analysis using three-dimensional laser Doppler velocimetry(LDV) measurement and computational analysis using the Reynolds stress model in FLUENT are conducted to give a clear understanding of the effect of blade loading on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition ($\Phi$=0.25) and two off-design conditions ($\Phi$=0.21 and 0.30). As the blade loading increases, the onset position of the rolling-up of tip leakage flow moves upstream and the trajectory of tip leakage vortex center is more inclined toward the circumferential direction. Because the casing boundary layer becomes thicker and the mixing between the through-flow and the leakage jet with the different flow direction is enforced, the streamwise vorticity decays more fast with the blade loading increasing. A distinct tip leakage vortex is observed downstream of the blade trailing edge at $\Phi$=0.30, but it is not observed at $\Phi$=0.21 and 0.25.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1074-1083
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• 2006

In the present study, the effect of blade rotation on blade heat transfer is investigated by comparing with the heat transfer results for the stationary blade. The experiments are conducted in a low speed annular cascade with a single stage turbine and the turbine stage is composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has a flat tip and the mean tip clearance is 2.5% of the blade chord. A naphthalene sublimation method is used to measure detailed mass transfer coefficient on the blade. For the experiments, the inlet Reynolds number is $Re_c=1.5{\times}10^5$, which results in the blade rotation speed of 255.8 rpm. Blade rotation induces a relative motion between the blade and the shroud as well as a periodic variation of incoming flow. Therefore, different heat/mass transfer patterns are observed on the rotating blade, especially near the tip and on the tip. The relative motion reduces the tip leakage flow through the tip gap, which results in the reduction of the tip heat transfer. However, the effect of the tip leakage flow on the blade surface is increased because the tip leakage vortex is formed closer to the surface than the stationary case. The overall heat/mass transfer on the shroud is not affected much by the blade rotation.

• The KSFM Journal of Fluid Machinery
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• v.12 no.2
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• pp.39-45
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• 2009

Leakage flow through turbine blade tip gap causes strong leakage vortex near the blade suction side and induces large aerodynamic losses. In this study, the conventional plane tip and various squealer tip blades were tested in a linear cascade in order to measure the effect of the tip shape on the total pressure loss. Three tip gap clearances of 0.6%, 1.3%, and 2.0% of blade span were tested. Flow measurement was conducted at one chord downstream from the trailing edge with a five-hole probe. Results showed that the leakage vortex was stronger than passage vortex and the mass averaged overall total pressure loss through the cascade was the lowest for suction side blade tip case. For all tested cases, the area averaged overall total pressure loss was increased as the tip clearance increased.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.619-622
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• 2002

It has been recognized that the flow in the blade passage of an axial turbomachinery rotor is very complex and is influenced by various flow phenomena, of which the tip leakage flow passing through the gap between rotor blade tip and casing plays a significant role. The losses produced due to the existence of the clearance have been known to be a large contributor of the rotor overall losses. Despite several experimental studies on non-rotating blade in the cascade configuration, and on actual rotating blades, the detailed nature of the complex flow phenomena associated with tip leakage, however, remains largely unresolved. Thus, a single-stage compressor test rig was built and measurements were taken at upstream and downstream of the rotor of this compressor at the aerodynamics laboratory of University of New South Wales. A five-hole probe and a hot-wire probe were used to measure mean and fluctuating flow parameters. The results show that tip leakage losses rise rapidly beyond tip gap of 0.01 Furthermore, the present project also identifies the regions in the wake behind the rotor of the axial compressor where such losses are concentrated. These results should be useful in the better design of rotors for improved performance of axial compressor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.3
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• pp.336-345
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• 1998

The substantial loss behind axial flow rotor was generated by wake, various vortices in the hub region and the leakage vortex in the tip region. Particularly, the leakage vortex formed near blade tip was one of the main causes of the reduction of performance, the generation of noise and the aerodynamic vibration in rotor downstream. In this study, the three-dimensional flowfields in an axial flow rotor for various tip clearances were calculated, and the numerical results were compared with the experimental ones. The numerical technique was based on SIMPLE algorithm using standard k-.epsilon. model (WFM). Through calculations, the effects of the tip clearance on the overall performance of rotor and the loss distributions, and the increase in the displacement, momentum, and blade-force-deficit thickness of the casing wall boundary layer were investigated. The mass-averaged flow variables behind rotor agreed well with the experimental results. The presence of the tip leakage vortex behind rotor was described well. Although the loci of leakage vortex by calculation showed some differences compared with the experimental results, its behavior for various tip clearances was clarified by examining the loci of vortex center.