• Journal of the Korean Society for Railway
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• v.19 no.3
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• pp.271-279
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• 2016

Pantograph aerodynamic noise is a major cause of noise that occurs when a train is traveling at high speeds. In this study, in order to analyze the contribution of pantograph aerodynamic noise, real train tests using HEMU-430X were carried out. In order to analyze the frequency characteristic of the noise of the pantograph in an actual vehicle, a sound field visualization has been carried out using a 144-channel microphone array at train speeds of 350 and 400km/h. As a result, it was confirmed that the low frequency noise in the 250~400Hz bandwidth provides the main contribution to the pantograph noise. And, in order to estimate the noise contribution of the pantograph, the noise level difference between cases in which the pantograph is ascending and those in which it is descending were compared in single microphone experiments. The frequency analysis in the single microphone tests showed that the bands of 315~400Hz and 1000~1250Hz are the main frequency characteristics of pantograph noise. These results show quite good agreement with those of previous studies and with results of sound field visualization.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.156-165
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• 2015

A survivability-analysis program has been developed to analyze the ground collision risk of atmospheric reentry objects, such the upper stages of a launch vehicle or satellites, which move at or near the orbital velocity. The aero-thermodynamic load during the free fall, the temperature variation due to thermal load, and the phase shift after reaching the melting point are integrated into the 3 degree-of-freedom trajectory simulation of the reentry objects to analyze the size and weight of its debris impacting the ground. The analysis results of the present method for simple-shaped objects are compared with the data predicted by similar codes developed by NASA and ESA. Also, the analysis for actual reentry orbital objects has been performed, of which results are compared with the measurement data.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.321-326
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• 2013

본 연구에서는 원형실린더의 강제 수평 및 수직진동에 따른 와흘림을 관찰하였다. EDISON_CFD의 가상경계법을 이용하여 원형실린더 주위 유동현상을 수치 모사하였다. 원형실린더의 강제 진동 특성에 따른 와흘림 진동수, 공력계수 등의 영향을 분석하였다. 특히, 진동방향에 따른 와흘림의 영향을 분석하여, 원형실린더의 강제 진동에 따른 유동의 선형성을 평가하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.2
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• pp.134-143
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• 2014

A significant degradation in the aerodynamic performance of wind turbine system can occur by ice accretion on the surface of blades operated in cold climate. The ice accretion can result in performance loss, overloading due to delayed stall, excessive vibration associated with mass imbalance, ice shedding, instrumental measurement errors, and, in worst case, wind turbine system shutdown. In this study, the effects of ice accretions on the aerodynamic characteristics of wind turbine blade sections are investigated on the basis of modern CFD method. In addition, the computational results are used to predict the performance of three-dimensional wind turbine blade system through the blade element momentum method. It is shown that the thickness of ice accretion increases from the root to the tip and the effects of icing conditions such as relative wind velocity play significant role in the shape of ice accretion.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.2
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• pp.99-107
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• 2014

In this study, aerodynamic characteristics of Kline-Fogleman airfoils are numerically investigatied which has been widely used in remote control aircraft operating at low Reynolds numbers. The comparison of aerodynamic characteristics was conducted between NACA4415 and Kline-Fogleman airfoil based on NACA4415. ANSYS Fluent was employed with the incompressible assumption and $k-{\omega}$ SST turbulence model. It was found that lift coefficient was significantly enhanced in the range of Reynolds number from $3{\times}10^3$ to $3{\times}10^6$. Especially in the region of Reynolds number below $2.4{\times}10^5$, the lift-to-drag-ratio was improved by 26% using the Kline-Folgeman airfoil compared with NACA4415 airfoil.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.2
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• pp.119-125
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• 2020

A high Reynolds number transonic wind tunnel has been built in 2018 at Agency for Defense Development(ADD). The tunnel has a closed circuit with a 1.5m×1.5m test section and is injection driven from a 140bar air supply system. The Mach number range is 0.3-1.2 with a conventional contracting nozzle and 1.4 with a convergent-divergent contraction. The stagnation pressure range is 100-550kPa at the lowest Mach number. An AGARD-B standard model is tested in the transonic wind tunnel to obtain 6-DOF aerodynamic coefficients. The results are compared with those obtained from ADD trisonic wind tunnel and others. We verify that the transonic wind tunnel become available to develop an aircraft from the testing results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.5
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• pp.399-406
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• 2016

The large scale wind turbine blades usually experience periodic change of inflow speed due to blade rotation inside the ground shear flow region. Because of the vertical wind shear, the inflow velocity in the boundary layer region is maximum at uppermost position and minimum at lowermost position. These spatial distribution of wind speeds can lead to the periodic oscillation of the 6-component loads at hub and low speed shaft of the wind turbine rotor. In this study we compare the aerodynamic loads between two inflow conditions, i.e, uniform flow (no vertical wind shear effect) and normal wind profile. From the computed results all of the relative errors for oscillating amplitudes increased due to the ground shear flow effect. Especially bending moment and thrust at hub, and bending moments at LSS increased enormously. It turns out that the aerodynamic analysis including the ground shear flow effect must be considered for fatigue analysis.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.648-651
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• 2010

Propeller shall have high efficiency and improved aerodynamic characteristics to get the thrust to fly at high speed for the FAR25 turboprop aircraft. That is way Clark-Y airfoil which is used to conventional turboprop aircraft propeller is selected as a blade airfoil. Javaprop program based on the Adkins method is used for aerodynamic design and analysis of propeller, Adkins method is based on the vortex-blade element theory which design the propeller to satisfy the condition for minimum energy loss. Slipstream displacement don't change and consider a rigid body. High efficiency propeller geometry is generated by varying chord length and pitch angle at design point of FAR25 turboprop aircraft. The propeller design results indicate that could be applied to the FAR25 turboprop aircraft, through analysis of propeller aerodynamic characteristics using the CFD(Computational Fluid Dynamic).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.6
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• pp.475-484
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• 2012

Numerical investigation is performed to understand the effects of thickness uncertainty of a supporting airfoil due to manufacturing processes on the aerodynamic characteristics of an airfoil used for measuring data in a wind tunnel testing. This is done by comparing the coefficients of lift, drag and moment of the airfoils. In this work, the airfoil model consists of three parts, one located in the center for measuring and two outer parts used for supporting. The study is carried out with a NACA64-418 airfoil and the turbulence model of Transition SST. It is found that the effect of thickness uncertainty of the airfoils used for supporting is not significant to the performance of the test airfoil at various angles of attack and Reynolds numbers.

• Journal of Aerospace System Engineering
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• v.13 no.1
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• pp.47-53
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• 2019

To improve an aerodynamic characteristic of the eVOTL aircraft, Korea Aerospace Research Institute (KARI) performed a validity test of the cross-rotating propeller technology. First, CFD analysis was carried out and an idea of the cross-rotating propeller to imply on a multi-copter confirmed with a commerce pitch control multi-copter that has two different blades, 0.11 and 0.21 m. After verifying the idea, a multi-copter with about 3 kg maximum take-off weight (MTOW) was custom designed to complete a ground test to measure thrust and noise. The test was performed with 15 and 22 in. propellers at the identical tip speed. The test results show that the 22 in. propeller with the cross-rotating technology required about 30 % less power and reduced 3~5 dB aerodynamic noise as compared to 15 in. propeller without cross-rotating.