• 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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• 2004.04a
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• pp.1975-1980
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• 2004

The three-dimensional flow in a turbine nozzle guide vane passage causes large secondary loss through the passage and increased heat transfer on the blade surface. In order to reduce or control these secondary flows, a linear cascade with a contoured endwall configuration was used and changes in the three-dimensional flow field were analyzed and discussed. Measurements of secondary flow velocity and total pressure loss within the passage have been performed by means of five-hole probes. The investigation was carried out at fixed exit Reynolds number of $4.0{\times}10^5$. The objective of this study is to document the development of the three-dimensional flow in a turbine nozzle guide vane cascade with modified endwall. The results show that the development of passage vortex and cross flow in the cascade composed of one flat and one contoured endwalls are affected by the flow acceleration which occurs in contoured endwall side. The overall loss is reduced near the flat endwall rather than contoured endwall.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.3
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• pp.241-255
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• 2012

Three types of 100 kW-class tidal stream turbines are proposed and their performance is studied both numerically and experimentally. Following a wind turbine design procedure, a base blade is derived and two additional blades are newly designed focusing more on efficiency and cavitation. For the three designed turbines, a CFD is performed by using FLUENT. The calculations predict that the newly designed turbines perform better than the base turbine and the tip vortex can be reduced with additional efficiency increase by adopting a tip rake. The performance of the turbines is tested in a towing tank with 700 mm models. The scale problem is carefully investigated and the measurements are compared with the CFD results. All the prediction from the CFD is supported by the model experiment with some quantitative discrepancy. The maximum efficiencies are 0.49 (CFD) and 0.45 (experiment) at TSR 5.17 for the turbine with a tip rake.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.11
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• pp.709-717
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• 2017

In this study, a model of two-stage Weis-Fogh type water turbine model is proposed, the hydrodynamic characteristics of this water turbine model are calculated by the advanced vortex method. The basic conditions and the motion of each wing are the same as that of the single-stage model previously proposed by the same author. The two wings (NACA0010 airfoils) and both channel walls are approximated by source and vortex panels, and free vortices are introduced from the body surfaces. The distance between the front wing axis and the rear wing axis, and the phase difference between the motion of the two wings, which is in phase and out of phase are set as the calculation parameters. For each case, the unsteady flow fields, pressure fields, force coefficients, and efficiency of the two wings are calculated, and the hydrodynamic characteristics of the proposed water turbine model are discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.269-274
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• 2014

In this study, low noise designs for a Savonius wind turbine were numerically investigated. As was reported in our previous study, the harmonic components with a fundamental frequency higher than the BPF were identified as being dominant in the noise spectrum of a Savonius wind turbine, and these components were a result of vortex shedding. On a basis of this observation, an S-shaped blade tip is proposed as a means of reducing the noise generated by small vertical(Savonius) wind turbines. This blade induces phase differences in the shedding vortices from the blades, and thus reduces the noise from the wind turbine. The aerodynamic noise characteristics of the conventional and "S-shaped" Savonius turbines were investigated by using the Hybrid CAA method where the flow field around the turbine is computed using the CFD techniques and the radiated noise are predicted by applying acoustic analogy to the computed flow field data. The degree of noise reduction resulting from the proposed design and its reduction mechanism were confirmed by comparing the predicted noise spectrum of these turbines and the flow characteristics around them.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.6
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• pp.813-821
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• 1997

Three-dimensional turbulent incompressible flow through the tip clearance of a linear turbine rotor cascade with high turning angle has been analyzed numerically. As a preliminary study to predict the tip clearance loss realistically, a generalized k-.epsilon. model derived by RNG (renormalized group) method is used for the modeling of Reynolds stresses to account for the strain rate of turbulent flow. The effects of the tip clearance flow on the passage vortex, the total pressure loss are considered qualitatively. The existences of vena contract and tip clearance vortex have been confirmed and it has been shown that as the size of the tip clearance increases, the accumulated flow through the tip clearance and the total pressure loss downstream of the cascade increase.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.8 s.239
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• pp.887-894
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• 2005

This paper describes effects of incidence angle on the wake turbulent flow of a high-turning turbine rotor blade. For three incidence angles of -5, 0 and 5 degrees, energy spectra as well as profiles of mean velocity magnitude and turbulence intensity at mid-span are reported in the wake. Vortex shedding fiequencies are obtained from the energy spectra. The result shows that as the incidence angle changes from -5 to 5 degrees, the suction-side wake tends to be widened and the deviation angle is increased. Strouhal numbers based on the shedding fiyequencies have a nearly constant value, regardless of the tested incidence angles.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.273-276
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• 2006

To generate electricity from wind energy, wind turbine generally has a rotor blade. Since this rotor blade is a kind of the rotating machinery, the wake from the rotor is very Important role in the side of the aerodynamic performances. Thus the study about wake is essential to analyze wind turbine aerodynamics. In this study wake characteristics are analyzed by hot-wire probe in the K.A.F.A(Korea Air Force Academy) wind tunnel. It is possible to analyze the wake characteristics by hot-wire probe from acquiring the velocity fluctuations at given positions in the flow. This velocity data are arranged by trigger signal at same azimuth of the blade in periodic manner of the rotor blade. From this various wake characteristics are found : radial and axial position of the tip vortex, vortex core characteristics in the flow etc.

• The KSFM Journal of Fluid Machinery
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• v.17 no.2
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• pp.12-23
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• 2014

A parametric study on anti-vortex holes for turbine blade cooling was investigated numerically. Three-dimensional Reynolds-averaged Navier-Stokes equations and shear stress transport turbulence model were used for analysis of anti-vortex film cooling. Validation of numerical results was carried out comparing with experimental data. The cooling performance of anti-vortex holes was assessed by two geometric variables, the ratio of diameters of holes and the lateral distances between the primary hole and anti-vortex hole at blowing ratios of 0.5 and 1.0. The results showed that the spatially-averaged film-cooling effectiveness increases as the ratio of the diameters increases and the distance between the primary hole and anti-vortex hole decreases.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.4
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• pp.336-343
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• 2009

Secondary flow losses can be as high as 30~50% of the total aerodynamic losses generated in the cascade of a turbine. Therefore, these are important part for improving a turbine efficiency. As well, many studies have been performed to decrease the secondary flow losses. The present study deals with the leading edge fences on a wing-body to decrease a horseshoe vortex, one of the factors to generate the secondary flow losses, and investigates the characteristics of the generated horseshoe vortex as the shape factors, such as the installed height, and length of the fence. The study was investigated using $FLUENT^{TM}$. Total pressure loss coefficient was improved about 4.0 % at the best case than the baseline.