• Journal of Advanced Marine Engineering and Technology
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• v.26 no.5
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• pp.596-606
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• 2002

The three-dimensional unsteady compressible Euler equation solver with ALE, CFD code, PAM-FLOW based on FEM method has been applied to analyze the flow field around the high speed train which is entering into a channel. From the present study, the pressure and flow transients were calculated and analyzed. The generation of compression wave was observed ahead of train and the high pressure in the gap between the train and the tunnel was also found due to the blockage effects. It was found that abrupt fluctuation in pressure exists in the region from train nose to shoulder of train corresponding to 10％ of total length of train during tunnel entry. Computed time history of aerodynamic forces of train during tunnel entry show that drag coefficient rapidly rises and saturates at about non-dimensional time 0.31. The total increase of drag coefficient before and after tunnel entry is about 1.1%. Transient profile of lift force shows similar pattern to drag coefficient except abrupt drop after saturation and lift force in the tunnel increases 0.08% more than that before tunnel entry.

• Wind and Structures
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• v.35 no.3
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• pp.193-211
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• 2022

The present study focuses on aerodynamic parameters behaviors and control on the single and double side setback building models at the buildings mid-height. The study is conducted by computational fluid dynamics (CFD) simulation. This study estimates the face wise pressure coefficient on single side setback buildings with a setback range of 20%-50% and double side setback buildings with setbacks ranging from 10%-25%. The polynomial fitted graphs from CFD data predict the Cp on different setback model faces within permissible limit ±13% error. The efficient model obtained according to the minimum drag, lift, and moment consideration for along and across wind conditions. The study guides the building tributary area doesn't control the drag, lift, and moment on setback type buildings. The setback distance takes a crucial role in that. The 20% double side setback model is highly efficient to regulate the moment for both along and across wind conditions. It reduces 17.5% compared to the 20% single side setback and 14% moment compared to the 10% double side setback models. The double side setback building is more efficient to control 4.2% moment than the single side setback building

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.631-638
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• 2003

The wind turbine blade is the equipment converted wind into electric energy. The effect of the blade has influence of the output power and efficiency of wind turbine. The design of blade is considered of lift-to-drag ratio, structure, a condition of process of manufacture and stable maximum lift coefficient, etc. This study is used the simplified method for design of the aerodynamic blade and aerodynamic analysis used blade element method. This process is programed by delphi-language. The program has any input values such as tip speed ratio, blade length, hub length, a section of shape and max lift-to-drag ratio. The program displays chord length and twist angle by input value and analyzes performance of the blade.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.2
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• pp.61-69
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• 2004

In this study, flow around rudder is analyzed by utilizing the numerical calculation, and the rudder open water test is performed to validate the calculation. The aim of this study is to design the new rudder shape to improve manoeuvring performance. In first, flow around two-dimensional rudder section is analyzed to understand the characteristics of section profile. And the calculation for all-movable rudders is performed and compared with results of rudder open water test. It is hard to numerically predict the drag force because the value is sensitive to the turbulence modeling and grid spacing near the wall. However, the lift force is predicted well. And we can prove that concave profile of the rudder section produce more lift and torque than convex one as a experiment. However PANEL method that ignore viscous effect cannot distinguish the difference of them. So, we can look for the numerical tool to be developed the new rudder shape.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.562-567
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• 2014

본 연구에서는 교육 및 연구를 위한 CFD 해석 프로그램인 EDISON_CFD를 이용하여 Symmetric airfoil(NACA0012)과 Cambered airfoil(NACA4412)의 뒷전 두께에 따른 공력 특성을 분석해보았다. Chord 길이의 0%, 1%, 2%, 3%, 4%에 해당하는 뒷전 두께를 가지는 Blunt trailing edge airfoil의 받음각에 따른 공력 특성을 비교 및 분석하고, 어떠한 장단점을 가지는지 확인하였다. 그 결과 Chord 길이의 1% 뒷전 두께를 가질 때를 제외하면 뒷전 두께가 두꺼워질수록 최대양력계수는 증가하였고, 양항비와 실속각은 감소하였다. 또한, 뒷전 두께가 두꺼워질수록 Symmetric airfoil에서는 받음각 $0^{\circ}$를 기준으로 양력곡선기울기가 증가하였고, Cambered airfoil에서는 전체적으로 양력계수가 증가함과 동시에 양력곡선기울기 또한 증가하는 것을 확인할 수 있었다.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.1-11
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• 2021

Performance of a NACA 63₄-021 hydrofoil in motion under and in close proximity of a free surface for a large range of angles of attack is studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally, for 0° ≤ AoA ≤ 30° at a Reynolds number of 10⁵. The results of the numerical study are in good agreement with the experimental results. The agreement confirms the new finding that for a submerged hydrofoil operating at high angles of attack close to a free surface, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil results in mitigation of the flow separation characteristics on the suction side of the foil and delay in stall, and improvement in hydrofoil performance. In comparing with a baseline case, results suggest a 55% increase in maximum lift coefficient and 90% average improvement in performance for, based on the lift-to-drag ratio, but it is also observed significant decrease of lift-to-drag ratio at lower angles of attack. Flow details obtained from combined finite volume and volume of fluid numerical methods provide insight into the underlying enhancement mechanism, involving interaction between the hydrofoil and the free surface.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.4
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• pp.447-459
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• 2012

The present study numerically investigates the effect of the wavy leading edge on hydrodynamic characteristics for the flow of rectangular wings with the low aspect ratio of 1.5. Five different wave lengths at fixed wavy amplitude have been considered. Numerical simulations are performed at a wide range of the angle of attack ($0^{\circ}{\leq}{\alpha}{\leq}40^{\circ}$) at one Reynolds number of $10^6$. The wavy wings considered in this study did not experience enough lift drop to be defined as the stall, comparing with the smooth wing. However, in the pre-stall region, the wavy wings reveal the considerable loss of the lift, compared to the smooth wing. In the post-stall, the lift coefficients of the smooth wing and the wavy wings are not much different. The pressure coefficient, limiting streamlines and the iso-surface of the spanwise vorticity are also highlighted to examine the effect of the wave length on the flow structures.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.217-220
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• 2006

The lift and drag forces produced by a wing of a given cross-sectional profile are dependent on the wing planform and the angle of attack. Aspect ratio is the ratio of the wing span to the average chord. For conventional fixed wing aircrafts, high aspect ratio wings produce a higher lift to drag ratio than low ones for flight at subsonic speeds. Therefore, high aspect ratio wings are used on aircraft intended for long endurance. However, birds and insects flap their wings to fly in the air and they can change their wing motions. Their wing motions are made up of translation and rotation. Therefore, we tested flapping motions with parameters which affect rotational motion such as the angle of attack and the wing beat frequency. The half elliptic shaped wings were designed with the variation of aspect ratio from 4 to 11. The flapping device was operated in the water to reduce the wing beat frequency according to Reynolds similarity. In this study, the aerodynamic forces, the time-averaged force coefficients and the lift to drag ratio were measured at Reynolds number 15,000 to explore the aerodynamic characteristics with the variation of aspect ratio. The maximum lift coefficient was turned up at AR=8. The mean drag coefficients were almost same values at angle of attack from $10^{\circ}$ to $40^{\circ}$ regardless of aspect ratio, and the mean drag coefficients above angle of attack $50^{\circ}$ were decreased according to the increase of aspect ratio. For flapping motion the maximum mean lift to drag ratio appeared at AR=8.

• Journal of Korea Water Resources Association
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• v.51 no.5
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• pp.405-415
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• 2018

Hydraulic variables such as discharge coefficient, gate opening, and upstream water depth are required to calculate the discharge of vertical lift gate. It is very important for a precise gate design, because it may affect the rest, to predict the behavior of gate opening during operation. In this study, an equation by which gate opening could be predicted with any upstream water depths was derived from the relation between the calculated value from buoyancy theory and measured one from experiment for a floating gate model. Downpull force was the reason for the differences between the calculated and the measured and it was verified using pressure coefficient. Also, the relation of discharge coefficient with gate opening ratios was derived. The derived relations were used for flood routing and it was realized that downpull force effect should be fully taken into account during gate design.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.174-180
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• 1999

Aerodynamic characteristics of tandem airfoil under ground effect is investigated numerically. Some numerical results for NACA 6409 tandem airfoil are presented. The numerical results show that as being decreased distance between airfoils, the lift coefficient of leading airfoil is increased and that of trailing airfoil is decreased. Drag coefficient shows opposite property, At the same distance between leading airfoil and trailing airfoil, lower position of trailing airfoil give better tandem airfoil effect.