• 한국항공우주학회지
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• 제35권10호
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• pp.859-867
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• 2007

본 논문의 목적은 다중로터의 공력특성 해석이 가능한 수치해석 기법을 개발하고 검증하는 것이다. 이를 위해 기 개발된 시간 전진 자유후류 모델이 고려된 비정상 용출 및 중첩 패널 코드에 table look-up 방식을 추가하여 로터 동력의 예측이 가능하도록 하였다. 또한, look-up table을 다양한 레이놀즈수 영역에서 적용하기 위해서 레이놀즈수 보정법을 사용하였다. 계산 결과는 동축 반전로터와 탠덤로터의 실험 결과를 이용하여 검증하였다. 동축 반전로터 검증에서 본 연구에서와 같이 블레이드의 두께효과가 고려되어 해석될 경우 실험치와 더 가까운 결과를 얻음을 확인하였다. 탠덤형 로터 검증 시 특정한 간격에서 와류 상호작용에 의한 와류 불안정성이 존재하였다. 이 경우 후류의 불안정성은 단일로터의 후류를 각 로터의 초기 후류형상으로 이용하는 방법을 통해 제거할 수 있었다. 검증된 코드를 이용하여 로터 간격에 따른 공력성능의 차이를 운동량 이론과 비교하였다.

• Journal of Ship and Ocean Technology
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• 제1권2호
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• pp.19-30
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• 1997

The accurate prediction of the flow and the pressure distribution near the tip of the blade is crucial in determining the tip vortex cavitation inception which usually occurs on the blade tip or inside the core of the tip vortex just downstream of the blade tip. An improved boundary element method is applied to the prediction of the flow around propeller blades, with emphasis at the tip region. In the method, the Blow adapted grid and a higher order panel method, which combines a hyperboloidal panel geometry with a hi-quadratic dipole distribution, are used in order to accurately model the trailing wake geometry and the highly rolled-up regions in the wake. The method is applied to several propeller geometries and the results have been found to agree well to the existing experimental data. Inviscid flow methods are able to predict the pressures at the tip as well as the shape of the trailing wake. On the other hand, they are unable to determine the flow inside the viscous core of the tip vortex, where cavitation inception often occurs. Thus, a method is presented that treats the flow inside the viscous core. The inner flow is treated with a 2-D Clavier-stokes solution without making any assumptions for axisymmetric flow and conicity of the flow along the tip trajectory. The method can thus allow the treatment of general propeller blade configurations. The velocity and pressure distributions inside the core are shown and compared to those from other numerical methods.

• 대한조선학회논문집
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• 제29권1호
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• pp.29-42
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• 1992

Spade Type 타의 단독 특성을 추정하기 위하여 3차원 Panel Method를 사용하였다. 입사류는 균일하며 시간에 따라 변하지 않는다고 가정하였고, 타 표면에 쏘오스 및 다이폴을 분포하였다. 후류면은 타의 뒷날에서 물체로부터 떨어져 나간다고 가정하였으며, 후류면에는 다이폴을 분포하였다. 후류면은 물체의 뒷날과 무한 원방에서 적당한 조건을 부여함으로써 그 형상을 가정하였으며, 후류 형상의 차이가 최종 결과에 미치는 영향을 고찰하였다. 뒷날에서는 3차원 압력 Kutta 조건을 적용하였으며, 2차원 Kutta조건을 적용한 결과와 비교하여 보았다. Spade Type 타에 대한 계산을 수행하였으며, 실험 결과와 전반적으로 잘 일치함을 확인하였다. 본 연구에서 사용한 방법은 타의 초기 설계 단계에서 유용하게 사용할 수 있을 것이다.

• International Journal of Aeronautical and Space Sciences
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• 제18권1호
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• pp.17-27
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• 2017

The treatment of rotor wake has been a critical issue in the field of the rotor aerodynamics. This paper presents a new free wake model for the unsteady analysis for a wind turbine. A blade-wake-tower interaction is major source of unsteady aerodynamic loading and noise on the wind turbine. However, this interaction can not be considered in conventional free wake model. Thus, the free wake model named Finite Vortex Element (FVE hereafter) was devised in order to consider the interaction effects. In this new free wake model, the wake-tower interaction was described by dividing one vortex filament into two vortex filaments, when the vortex filament collided with a tower. Each divided vortex filaments were remodeled to make vortex ring and horseshoe vortex to satisfy Kelvin's circulation theorem and Helmholtz's vortex theorem. This model was then used to predict aerodynamic load and wake geometry for the horizontal axis wind turbine. The results of the FVE model were compared with those of the conventional free wake model and the experimental results of SNU wind tunnel test and NREL wind tunnel test under various inflow velocity and yaw condition. The result of the FVE model showed better correlation with experimental data. It was certain that the tower interaction has a strong effect on the unsteady aerodynamic load of blades. Thus, the tower interaction needs to be taken into account for the unsteady load prediction. As a result, this research shows a potential of the FVE for an efficient and versatile numerical tool for unsteady loading analysis of a wind turbine.

• International Journal of Aeronautical and Space Sciences
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• 제16권3호
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• pp.325-338
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• 2015

Experimental and numerical investigations were conducted to identify the wake characteristics downstream of two vane-type vortex generators over laminar flat plate boundary layer. Experimental study was carried out by using the stereoscopic particle image velocimetry. To describe the flow field around the vortex generator in detail, numerical study was performed. We considered two different planform shapes of vortex generator: triangular and rectangular shape. The height of the generator was chosen to be about the boundary layer thickness at the position of its installation. Two different lengths of the generator were chosen: two and five times the height. Wake measurements were carried out at three angles of attack for each configuration. Wake characteristics for each case such as overall vortical structure, vorticity distribution, and location of vortex center with downstream distance were obtained from the PIV data. Wake characteristics, as expected, were found to vary strongly with the geometry and angle of attack so that no general tendency could be deduced. Causes of this irregular tendency were explained by using the results of the numerical simulation.

• 산업기술연구
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• 제5권
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• pp.51-57
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• 1985

The object of this study is in the development of the computer program to predict the performance of rotor in hovering by getting the aerodynamic load acting on blade. For this work the vortex theory was chosen among the aerodynamic theories, blade was replaced by planar vortex panels, and prescribed wake for the wake geometry was selected and then represented by vortex lattices. To get the aerodynamic load on blade, flow was assumed to be incompressible, irrotational and steady, and the surface boundary condition of inviscid flow was used as boundary condition. Then the relationships between this load and flight condition and blade geometry were examined.

• 산업기술연구
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• 제8권
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• pp.31-35
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• 1988

To predict the airloads on helicopter rotors in hover, the doublet panel method of the first order is applied. For this simulation, the rotor blade is divided into many panels both in spanwise and in chordwise direction, and Kocurek-Tangler's prescribed wake with roll-up process is taken for determing wake geometry and then represented by vortex lattice. To abtain more physically realistic calculation of induced velocity, the vortex core model is adopted and the compressibility effect is considered by Karman-Tsien rule.

• 대한기계학회논문집B
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• 제22권2호
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• pp.240-252
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• 1998

The purpose of this study is to develop a method for predicting the aerodynamic performance of the low speed airfoils in the 2-dimensional, steady and viscous flow. For this study, the airfoil geometry is specified by adopting the longest chord line system and by considering local surface curvature. In case of the inviscid incompressible flow, the analysis is accomplished by the linearly varying strength vortex panel method and the Karman-Tsien correction law is applied for the inviscid compressible flow analysis. The Goradia integral method is adopted for the boundary layer analysis of the laminar and turbulent flows. Viscous and inviscid solutions are converged by the Lockheed iterative calculating method using the equivalent airfoil geometry. The analysis of the separated flow is performed using the Dvorak and Maskew's method as the basic method. The wake effect is also considered by expressing its geometry using the formula of Summey and Smith when no separation occurs. The computational efficiency is verified by comparing the computational results with experimental data and by the shorter execution time.

• 대한조선학회논문집
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• 제45권4호
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• pp.353-360
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• 2008

A numerical model for the analysis of the marine propeller including wake roll-up is presented. In this study, we apply a higher-order panel method, which is based on a B-spine representation for both generations of the propeller geometry and hydrodynamic solutions, to predict the flow around the propeller blades. The present model is validated by comparison of the experimental measurements. The results show that the present method is able to predict the improved pressure distributions on the blade surface, especially very close to propeller tip regions, where other panel methods without the wake roll-up model give erroneous results.

• Journal of Advanced Marine Engineering and Technology
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• 제18권1호
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• pp.101-113
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• 1994

This research has presented and experimental investigation on the characteristics of turbulent wake past a rectanular cylinder, according to various width/height ratio such as B/H=2.0, 2.79, 3.0, and 4.0 in a uniform shear flow. In order to perform this study, a special shear flow generator which produces the uniform shear flow has been designed and manufactured. It is found that the characteristics of the wake in a uniform shear flow are quite different from those of a uniform flow and vary with shear rate. And also, the formation of regular vortex structure is concerned with shear rate.