• Journal of Advanced Marine Engineering and Technology
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• v.36 no.6
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• pp.808-813
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• 2012

The Characteristics of the drag reduction of a square prism having a detached splitter plate at the wake side were investigated by measuring of lift and drag on the square prism. The experimental parameters were the width ratios(H/B=0.5~1.5) of splitters to the prism width and the gap ratios (G/B=0~2) between the prism and the splitter plate. As the results the amplitude of the lift on the square prism having a detached splitter plate was remarkably decreased by comparison with the prototypical square prism. The drag reduction rate of the square prism was increased with H/B in case of the same G/B, and was increased and decreased with G/B in case of the same H/B. The maximum drag reduction rate was represented by 24.2% at H/B=1.5 and G/B=0.5.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.3
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• pp.243-247
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• 2015

The characteristics of the fluid force reduction of a square prism having a small triangular prism at the upstream side was investigated by measuring of lift and drag on the square prism The experimental parameters were the width ratios (H/B=0.2~0.6) of triangular prisms to the prism width and the gap ratios (G/B=0~3) between the square prism and the triangular prism. The drag reduction rate of the square prism was increased and then decreased with G/B in case of the same H/B, and was increased with H/B in case of the same G/B. The maximum drag reduction rate was represented by 78.5% at H/B=0.6 and G/B=1.5. The lift reduction rate of the square prism was hardly not affected by the width and gaps ratios, the average value was about 52.4%.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.1
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• pp.94-100
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• 2012

The passive control by vertical splitter plate of fluid force acting on a square prism near a plane wall was studied by measuring of fluid force on the prism and by visualization of the flow field using PIV. The hight of the splitter plate was 10% of the square width. The experimental parameters were the attaching position of vertical splitter plate and the space ratios G/B to the prism height. Time variation of vorticity was most remarkable at 3.0B(B: prism height) position toward wake direction from the center of the prism. The point of inflection of average lift coefficient and Strouhal number on the prism were represented at the space ratio G/B=0.4~0.6 for the prism having vertical splitter plate. The drag of the prism was reduced average 5.0% with the space ratios by attaching the vertical splitter plate at the upper and rear corner on the prism. In this case, the size of the separated region on the upside of the prism was smaller than that of prism having no the splitter plate.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.2
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• pp.156-162
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• 2013

The characteristics of the unsteady flowfield of a square prism having a detached splitter plate at the wake side were investigated by advanced vortex method. The instantaneous and average velocity field and pressure field around a square prism without and having splitter plate were calculated by forcing the gap ratio having the maximum drag reduction rate, at Reynolds number $Re=1.0{\times}10^4$ and the width ratio H/B=1.0 of splitter to the prism width. The drag and lift coefficients on the square prism were also obtained. The calculated results agree with the measured drag coefficients and pressure distributions on the square prism. The vortices of the opposite direction at upside and down side of the splitter plate were generated by installing of the plate. And the drag on the square prism was decreased by increasing of the pressure of back face of the prism with the vortices.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.7
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• pp.435-443
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• 2017

The Characteristics of the flowfields of a square prism having a small square prism were investigated by measuring of lift and drag on the square prism and visualizing the flowfield using PIV. The experimental parameters were the width ratios(H/B=0.2~0.6) of small square prisms to the prism width and the gap ratios (G/B=0~3) between the prism and the small square prism. The drag reduction rate of the square prism initially increased and then decreased with the G/B ratio for the same H/B ratio, and increased with the H/B ratio for the same G/B ratio. The maximum drag reduction rate of 98.0% was observed at H/B=0.6 and G/B=1.0. The lift reduction rate of the square prism was not affected by the width and gap ratios; the total average value was approximately 66.5%. In case of a square prism having a small square prism, the stagnation regions were represented in the upstream and downstream sides of the square prism.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.3
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• pp.198-204
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• 2016

The characteristics of the flow field of a circular cylinder having a small vertical plate at the upstream side are investigated by measuring the fluid force on the circular cylinder and by visualizing the flow field using particle image velocimetry. The experimental parameters are the width ratios (H/B = 0.2-0.6) of the vertical plates to the circular cylinder's diameter, and the gap ratios (G/B = 0-3) between the circular cylinder and the vertical plate. The drag reduction rate and Strouhal number of the circular cylinder increased and then decreased with G/B in the case of the same H/B. The drag reduction rate increased with H/B in the case of the same G/B. In the case of a circular cylinder having a small vertical plate, the stagnation regions are represented on the upstream and downstream sides of the circular cylinder, and the size of that region on the upstream side increased with H/B.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.400-403
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• 2007

소형 풍력터빈 설계 시 고려해야 할 익형의 선택, 익형의 붙임각 및 Solidity 등이 터빈의 성능에 미치는 영향을 고찰하였다. 한 개의 익형에 대한 공력계수를 이용하여 수학적 모델링을 통하여 최적 붙임각을 예측하여 경향을 파악하였다. 받음각에 따른 익형의 공력특성을 CFD 기법으로 파악한 후 5개의 Blade를 갖는 Turbine의 성능을 익형의 붙임각에 따라 파악하여 최대 성능을 갖는 붙임각을 최종 산출하였다. 익형 선정시 받음각에 대한 양력/항력 곡선을 이동시키는 캠버 익형의 기능보다는 항력 대양력의 비(L/D) 가 최대인 익형을 선정하는 것이 더욱 중요하며, Blade수가 적을수록 Torque의 양은 증가하고 Blade가 6이상이변 효율이 급격히 감소함을 알 수 있다.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.900-908
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• 2014

The Characteristics of the flowfields of a square prism having a small vertical plate at the upstream side was investigated by measuring of fluid force on the square prism and by visualization of the flow fields using PIV. The experimental parameters were the width ratios(H/B=0.2~0.6) of vertical plates to the prism width and the gap ratios (G/B=0~3) between the prism and the vertical plate. The drag reduction rate of the square prism was increased with H/B in case of the same G/B, and was increased and then decreased with G/B in case of the same H/B. The lift reduction rate of the square prism was hardly not affected by the width and gaps ratios, the average value was about 48.1%. In case of a square prism having a small vertical plate, the stagnation regions were represented in the upstream and downstream sides of the square prism.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.5
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• pp.625-631
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• 2011

The passive control of fluid force acting on a square prism near a plane wall was studied by attaching horizontal splitter plate on the corner of the prism. The width of the splitter plate was 10% of the square width. The experiments were performed by measuring of fluid force on the prism and by visualization of the flow field using PIV. The experimental parameters were the attaching position and the space ratios G/B between the prism and wall. The flow between the prism and wall was remarkable and Karman vortex in the wake of the prism was considerable in the space ratio over 0.4. The point of inflection of average lift coefficient and Strouhal number on the prism were represented at the space ratio G/B=0.4 for the prototype prism and G/B=0.6 for the prism having horizontal splitter plate. The drag of the prism was reduced average 4.5% with the space ratios by attaching the horizontal splitter plate at the rear and lower corner on the prism. In this case, the size of the separated region on the upside of the prism was smaller than that of prism without the splitter plate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.2
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• pp.137-145
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• 2008

An experimental study was performed in order to investigate the influence of Reynolds number on the drag coefficient variations of an oscillating airfoil. A NACA 0012 airfoil was sinusoidally pitched at the quarter chord point with an oscillating amplitude of ${\pm}6^{\circ}$. The free-stream velocities were 1.98, 2.83 and 4.03 m/s and the corresponding chord Reynolds numbers were $2.3{\times}10^4$, $3.3{\times}10^4$ and $4.8{\times}10^4$, respectively. The drag coefficient was calculated from the ensemble average velocity measured by an X-type hot-wire probe(X-type, 55R51) in the near-wakes region. In the case of Re=$2.3{\times}10^4$, variation of drag coefficient shows a negative damping (counter-clockwise variation), which implies an unstable state which could be excited by aerodynamic force, whereas the drag coefficient represents the positive damping (clockwise variation) as the Reynolds number increases from Re=$3.3{\times}10^4$ to $4.8{\times}10^4$. Hence, the drag coefficient variations show significant differences between Re=$2.3{\times}10^4$ and $4.8{\times}10^4$이다.