• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.7
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• pp.755-762
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• 2004

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.12
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• pp.1059-1066
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• 2007

An experimental study has been conducted to investigate the flow separation control effects of a blowing jet on an elliptic airfoil at a Reynolds number of 7.84×105 based on the chord length. A blowing jet was obtained by pressing a plenum inside the airfoil and ejecting flow out of a thin jet slot that located in leading edge or trailing edge. The experimental results have shown that the blowing jet had an effect of suppressing the flow separation, resulting in the higher suction pressure distribution and higher normal force. The increase in Cn was more pronounced at higher incidence, whereas the effectiveness of the blowing jet reduced at lower incidences. The leading edge pulsating blowing with 90° was the most effective in controlling the flow separation than other types of blowing jet configuration tested in this research. Moreover, when the pulsating blowing was applied, the stall angle was postponed about 2°-3°. The continuous and pulsating blowing jet is a direct and effective flow separation control for improving the aerodynamic characteristics and performances of airfoil.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.6
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• pp.533-539
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• 2015

Recently, guided missiles applies folding wings to save space. During wing deployment, aero force acting on wing effects significantly on deployment performance, usually aerodynamic coefficient are calculated by CFD analysis. However, Missile Datcom can calculates estimated aerodynamic coefficient very quickly by assuming wing deployment motions as dihedral angle of wing. If missile has external store, wings may need to be folded on top of each other. In this case, one of wing help or interrupt other wing deployment, locking effect. In this study, both effects were included on wing deployment performance analysis to criteria for wings locked condition and formulated wing deploy performance, and compared with wind tunnel test data. Analysis predicted vulnerable wind direction of wing deployment very well.

• Korean Journal of Weed Science
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• v.5 no.2
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• pp.155-163
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• 1985

Three pyrazole-herbicides, pyrazolate, pyrazoxyfene and benzophenap, were evaluated for their interaction in controlling barnyardgrass (Echinochloa crusgalli) with two chloroacetamide-herbicides, butachlor and pretilachlor. Percent inhibition of barnyardgrass growth by pyrazolate, pyrazoxyfene, and benzophenap was 44%, 64%, and 0%, respectively, when each was applied at the 1.5 leaf-stage of barnyardgrass at a rate of 3㎏ ai per ㏊ as single treatment, and the benzophenap showed 60% inhibition when it was applied at the coleoptile stage. While the lowest rate controlling the 1.5 leaf-stage barnyardgrasses by 98 to 100% of the butachlor and pretilachlor was 1.5㎏ and 200g per ㏊, respectively. All of the combinations of pyrazolate with butachlor, pyrazoxyfene with pretilachlor, and benzophenap with butachlor have shown synergistic interaction in controlling barnyardgrass on the Chisaka's isobole of 90% growth inhibition as well as on the Colby`s interaction efficacy data; synergism indices were 2.44, 1.62 and 1.52 in order. The dose combinations shown the maximal synergism were 1870g of pyrazolate with 140g of butachlor (1:0.075), 33008 of pyrazoxyfene with 338 of pretilachlor (1:0.01), and 3350g of benzophenap with 520g of butachlor (1:0.15) on the ai/㏊ basis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.3
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• pp.197-209
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• 2018

In this study, numerical analyses on Quad Tilt Rotor(QTR) are carried out to investigate the interference effect of components and effect of operating condition during forward flight. Actuator Surface Method(ASM) which is implemented in an open source CFD code, OpenFOAM, is used to calculate the flow field around QTR with high computational efficiency. The lift of the front and rear wing is found to increase or decrease depending on the rotation direction of the rotor. At the rear wing, the interference effects of the front and rear rotor appear as a combined manner. Performance change due to the phase difference is found to be insignificant. For both rotors, the locally higher thrust is generated by the blockage effect of the wing. The interference effect of wake from the front nacelle contributes to higher local thrust for the rear rotor compared to the front rotor. And it is observed that the amplitude of thrust oscillation can decrease depending on the phase difference between the rotors. Aerodynamic performances of both rotors and the entire aircraft were compared and analyzed for various operating conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.11
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• pp.933-940
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• 2016

A comparative study between a wind tunnel test and an XFOIL simulation looking at the aerodynamic performance of the airfoil for MW-class wind turbine was conducted for validation in the design stage. Tests are carried out for 21% and 30% thickness-ratio airfoils developed for 5 ~ 10 MW offshore wind turbine and the results are compared with the output from the XFOIL simulation at Reynolds number $1.0{\times}10^7$. The test is performed at a free-stream velocity of 50 m/s, corresponding to a Reynolds number of $2.2{\times}10^6$ based on the chord. Surface roughness is simulated using a zig-zag tape. Discrepancies between the results of the test and the XFOIL analysis are found, however, meaningful data for surface pressure distribution, basic performance and surface roughness effect are obtained from the tests, while useful lift-to-drag ratio data is found by the XFOIL simulation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.3
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• pp.177-182
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• 2007

The effects of three fuselage head shapes and nonplanar ground surface on the aerodynamic characteristics of FAST fuselages are investigated using a boundary element method. Wind tunnel test is also performed to validate the present method and to identify the wall effect on the frictional drag which cannot be analyzed using the present method. It is found that the channel has an effect of increasing the lift of those investigated fuselages. The optimal head shape depends on the design conditions of the FAST and its guideway channel. Comparing the calculated induced drag with the measured total drag, it can be concluded that the profile drag is independent of the ground height. Thus, the present numerical method can be applied to the conceptual design of the high-speed ground transporters if only the profile drag of the vehicle in free flight is assumed to be known.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.47-53
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• 2004

An Experimental investigation into the effects of the blowing jet type and jet orientation on the aerodynamic characteristics over an elliptic type airfoil is explored. This study is aimed at expanding the data base of blowing jet application in separation control of elliptic airfoil. Present data includes: surface pressure, blowing jet exit velocity measurements and integrated aerodynamic loads. The experiments were performed for an elliptic airfoil at Reynolds number $8.22{\times}10^5$. The improvement of effects of pulsed jet on the increase of aerodynamic characteristics was significant for the post-stall angle. For reduced mass flow rates, pulsed jet allowed considerably higher lift to be generated. The jet orientation also showed dominant parameter on the separation control Positive jet angle delay or avoid separation, whereas negative jet angle promotes it.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.955-965
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• 2010

The MH-75 propeller for the MAV propulsion is designed using a free vortex design method which considers design parameters such as the hub-tip ratio, the twist angle distribution, the maximum camber location and the chord length of the propeller blade. Aerodynamic characteristics of the MH-75 propeller are predicted by changing the flight speed using the frequency domain panel method. And, the thrust characteristics of the MH-75 propeller are measured using the balance system of the subsonic wind tunnel for the validation of numerical results. The performance characteristics of the MH-75 propeller satisfied with design requirements. Numerical results of the MH-75, which are predicted by the frequency domain panel method, are more agree with experimental results compare with XFOIL.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.10
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• pp.859-867
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• 2007

The objective of this study is to develop and validate a numerical method which can handle the multi-rotor aerodynamic characteristics. For the purpose of power estimation, table look-up method is implemented to the existing unsteady panel code that is coupled with a time-marching free wake model. Also, the Reynolds number scaling is implemented for the application to various regions of Reynolds number. The computed results are validated against the available experimental data for coaxial and tandem rotors. In the validation case for the coaxial rotor, more accurate result is acquired when the thickness effect is considered. The wake instability problem occurs at a particular separation distance between the rotors for tandem rotors. The wake instability is avoided by setting the single-rotor wake geometry as the initial wake geometry for the multi-rotor analysis. The estimated result for rotor separation effect is compared with the result of the momentum theory.