• International Journal of Aeronautical and Space Sciences
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• v.13 no.3
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• pp.317-322
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• 2012

The low speed aerodynamic characteristics for a modified sonic arc airfoil which is designed by using the nose shape function of sonic arc, the shape function of NACA four-digit wing sections, and Maple are experimentally investigated. The small rotor blades of a modified sonic arc and NACA0012 airfoil are precisely fabricated with a commercially available light aluminum(Al 6061-T6) and are spin tested over a low speed range (3000rpm-5000rpm). In a consuming power comparison, the consuming powers of NACA0012 are higher than that of modified sonic arcs at each pitch angle. The measured rotor thrust for each pitch angle is used to estimate the rotor thrust coefficient according to momentum theory in the hover state. The value of thrust coefficients for both two airfoils at each pitch angle show almost constant values over the low Mach number range. However, the rotor thrust coefficient of NACA0012 is higher than that of the modified sonic arc at each pitch angle. In conclusion, the aerodynamic performance of NACA0012 is better than that of modified sonic arcs in the low speed regime. This test model will provide a convenient platform for improving the aerodynamic performance of small scale airfoils and for performing design optimization studies.

• International Journal of Naval Architecture and Ocean Engineering
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• v.1 no.2
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• pp.64-69
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• 2009

The two-dimensional unsteady flow around a vertical axis turbine for tidal stream energy conversion was investigated using a computational fluid dynamics tool solving the Reynolds-Averaged Navier-Stokes equations. The geometry of the turbine blade section was NACA653-018 aiifoil. The computational analysis was done at several different angles of attack and the results were compared with the corresponding experimental data for validation and calibration. Simulations were then carried out for the two-dimensional cross section of a vertical axis turbine. The simulation results demonstrated the usefulness of the method for the typical unsteady flows around vertical axis turbines. The optimum turbine efficiency was achieved for carefully selected combinations of the number of blades and tip speed ratios.

• Journal of Wind Energy
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• v.13 no.4
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• pp.42-49
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• 2022

Today, the power capacity of a wind turbine and the size of a blade is increasing to capture more wind resources, reduce the number of wind turbines on a wind farm, and reduce the cost of energy. As the blade size becomes larger, attention is being paid to the structural integrity of the blade root connection due to the heavy gravitational load effect and increased aerodynamic loads on the large blade, which could cause catastrophic failure of the blade. Therefore, the secure bolted joint connection of the blade to the hub is very important. In this paper, attention was given to the stress concentration factor (SCF) at the first thread between the M42 bolt and nut. The effect of various design parameters on the stress concentration factor was investigated, which included nut type, nut height, and reduced shank bolt. From a close design investigation of the numerical results, it turned out that the use of a reduced shank bolt resulted in the largest reduction of the stress concentration factor by 40 %, and the round nut type also reduced the SCF by 10 %, which will be beneficial to large wind turbine blades over 100 meters.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.29-40
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• 1999

A numerical method in frequency domain for the analysis of the acoustic wave equation governing the sound field generated by a non-cavitating propeller under a steady of unsteady loading condition is developed. Theory shows that only multiples of the blade passage frequency exist and that the wave number consists of the frequency component due to the nonuniformity of the wake and the Doppler effect originated from the rotation of the blades. Correlation with experiments for a two bladed propeller, designed to be load-free at a particular advance speed, indicate that the thickness effect can be significant in steady case, but can be negligible compared to the unsteady loading effect.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.159-165
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• 2008

A sirocco fan is widely used for discharging pollutants of a kitchen space since it is able to generate a relatively high air flow rate considering its small size and makes less noise than a axial fan or a centrifugal fan. However, it has a problem because its efficiency is low, and power consumption is larger. Performance of a sirocco fan is influenced by various factors such as number of the fan blades, diameter of the fan, geometry of the fan, geometry of its housing, revolution frequency, static pressure condition, and etc. This research investigated the effect on the performance of geometry of the housing. For CFD analysis, we used a commercial code, SC/Tetra, and used a sliding mesh method to give the same condition as an actual state. Verification of the CFD results is done by comparison of experimental data and numerical one about the suction flow rate, and it is confirmed that two results are well consistent. After we changed the shape of housing according to Archimedes' screw, we observed that suction efficiency is improved by 10.7% maximum.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.4
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• pp.411-416
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• 2008

A strength problem of propeller blades for large container ships at astern condition has been occasionally reported due to the application of a highly skewed propeller which can reduce the hull surface fluctuation forces. A finite element analysis code for propeller blade was developed and utilized since 1985. Recently, however, further fine mesh modeling for finite element analysis is required to yield higher accuracy in the analysis. The present study shows an application of FE analysis code to the highly skewed propeller for large container ships. Results of FE analysis show that the number of FE mesh affects largely on strength, and also the calculated strength with fine mesh gives good agreements to those of other FEM codes. A method to enlarge strength near the trailing edge was introduced considering the strength criterion on the blade.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.30 no.4
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• pp.57-64
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• 2022

A study on propllers for unmaned aerial vehicles is conducted using the open softwares. Since the shape of the propeller is closely related to the thurst characteristics of the propulsion system, adopting an appropriate propeller will significantly reflect stable aerodynamic performances. In this study, propellers for unmanned aerial vehicles were modeled by using OpenVSP and Propel for comparison, the thrust characteristics according to the number of blades and the diameter of the propeller were analyzed. In addition, the tendency of thrust characteristics according to various propeller pitch angles was confirmed. Based on the analysis results of this study, the applicability of the propeller shape to the design of the unmanned aerial vehicle was confirmed. It is shownthat the analysis results of this study can be utilized when modeling the propeller shape in research such as a conceptual design of unmanned aerial vehicle. In this case, it should be noted that OpenVSP does not involve the viscous effect of air.

• The KSFM Journal of Fluid Machinery
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• v.3 no.2 s.7
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• pp.31-35
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• 2000

In this research, the performance predictions of the submersible mixer were investigated. The variation of the performance characteristics by changing the impeller design parameters were discussed through the flow calculation results by using a commercial program, FLUENT. The performance of the submersible mixers is related to the velocity diffusion profiles downstream of the impeller and also the required input motor power to mix the fluid. In this study, the various design parameters such as the number of blade, the hub and tip diameters, the impeller blade profiles and revolution speed of the blades were taken for the fixed values. The blade sweep direction, the chord length distribution along with the radius of the blade and the inlet blade angle were changed to make different testing models. The flow calculation results show the effect of the changed design parameters on the performance of the submersible mixers and also give some helpful information for designing more efficient submersible mixers.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.361-369
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• 1996

The accurate prediction of modal parameters of a rotating blade is an important requirement in the assessment of the dynamics of a helicopter rotor. Indeed, predictions of flight loads and stability are normally dependent on initially predicting the undamped mode shapes. A measuring technique, known as Strain Pattern Analysis (SPA), appears to be the most successful technique for measuring the mode shapes of rotating blades. This method was developed to be used on actual aircraft so no attempt was made to measure rotating mode shapes directly in order to validate the SPA method. This report summarizes results from experimental investigations which were carried out to validate the SPA method for the prediction of aerodynamically damped modes of a rotating blade. A series of modal tests were carried out on two rotor models in which the non-rotating, undamped and aerodynamically damped rotating modes were measured directly (strain and displacement patterns). It is shown that the SPA method to be very successful in itself but there are a number of limitations in validating this technique. To provide data which could be used to confidently validate theoretical prediction codes, existing limitations should be addressed.

• Journal of Power System Engineering
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• v.19 no.5
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• pp.32-37
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• 2015

The present study is to investigates the convective heat transfer characteristics and pressure drop inside the rib-roughened cooling passage of gas turbine blades. The divergent rectangular channel is fabricated with V-shaped ribs on one wall only and the inlet hydraulic diameter to outlet hydraulic diameter ratio($D_{ho}/D_{hi}$) of 1.49 is used. The current investigation has covered a Reynolds number (Re) range of 22,000~75,000, relative roughness height ($e/D_h$) of 0.1~0.2, and rib angle of attack (a) of $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$ for a fixed relative pitch of 10. Results show that the Nusselt numbers are the greatest in the $60^{\circ}$-angled ribs; however, the total friction factors are the highest in the $30^{\circ}$-angled ribs.