• 한국군사과학기술학회지
• /
• 제5권3호
• /
• pp.77-86
• /
• 2002

An experimental study of the vortex interaction characteristics of a delta wing/LEX configuration was conducted in a wind tunnel using the micro water droplet and laser beam sheet visualization technique. The main focus of this study was to analyze the effect of the angle of attack and sideslip angle on the vortex interaction and vortex breakdown. These tests were accomplished at angles of attack between $16^{\circ}$ and $28^{\circ}$ and sideslip angle between $0^{\circ}$ and $-15^{\circ}$ at free-stream velocity of 6.2 m/s. Flow visualization data provide a description of the vortex interaction between LEX and wing vortices, and of the vortex breakdown. The introduction of LEX vortex stabilized the vortical flow, and delayed the vortex breakdown up to higher angle of attack. The vortex interaction and breakdown was promoted on the windward side, whereas they are suppressed on the leeward side.

• 대한기계학회논문집B
• /
• 제33권8호
• /
• pp.580-588
• /
• 2009

This paper summarizes the experimentally-measured performance of small-scale, vertical-axis wind turbine for the purpose of improving the aerodynamic efficiency and its controllability. The turbine is designed to have a Savonius-Type rotor with an inlet guide-vane and an side guide-vane so that it achieves a higher efficiency than any lift- or drag-based turbines. The main design factors for this high-efficient, vertical wind turbine are the number of blades (Z), and the aspect ratio of Height/Diameter (H/D) among many. The basic model has the diameter of 580mm, the height of 464mm, and the blade number of 10. The maximum power coefficient of 0.50 was experimentally measured for the above-mentioned specifications. The inlet-guide vane ensures the maximum efficiency when the angle of attack to the rotor blade lies between $15^{\circ}$ and $20^{\circ}$. This experimental results for the vertical-axis wind turbine can be applied to the preliminary design of turbine output curve based on the wind characteristics at the proposed site by controlling its aerodynamic performance given as a priori.

• 대한기계학회논문집
• /
• 제18권10호
• /
• pp.2664-2674
• /
• 1994

Drag, lift, and pitching moment measurements have been made on a range of slanted-base ogive cylinders, using the KANOMAX wind tunnel and balance system. Test Reynolds numbers(based on model maximum diameter) varied from $0.54{\times}10^{5}{\;}to{\;}1.56{\times}10^{5}$. Crossflow velocity maesurement was conducted by 5-hole pitot tube at $Re_{D}=1.46{\times}10^{5}$. For two base angle $({\theta}=30$ and 45 deg.), aerodynamic forces and moment were measured with increasing angle of attack(0~30 deg.). Two types of wake flow were observed, a quasisymetric turbulent closure or a longitudinal vortex flow. Aerodynamic characteristics differ dramatically between the two wake types. It was found that the drag, lift and pitching moment coefficients increased with increasing angle of attack.

• Wind and Structures
• /
• 제28권4호
• /
• pp.255-270
• /
• 2019

Aerodynamic configurations of bridge decks have significant effects on the aerostatic torsional divergence and flutter forsuper long-span bridges, which are onset for selection of suitable bridge decksfor those bridges. Based on a cable-stayed bridge with double main spans of 1500 m, considering typical twin-box, stiffening truss and closed-box section, which are the most commonly used form of bridge decks and assumed that the rigidity of those section is completely equivalent, are utilized to investigate the effects of aerodynamic configurations of bridge decks on aerodynamic instability performance comprised of the aerostatic torsional divergence and flutter, by means of wind tunnel tests and numerical calculations, including three-dimensional (3D) multimode flutter analysis and nonlinear aerostatic analysis. Regarding the aerostatic torsional divergence, the results obtained in this study show twin-box section is the best, closed-box section the second-best, and the stiffening truss section the worst. Regarding the flutter, the flutter stability of the twin-box section is far better than that of the stiffening truss and closed-box section. Furthermore, wind-resistance design depends on the torsional divergence for the twin-box and stiffening truss section. However, there are obvious competitive relationships between the aerostatic torsional divergence and flutter for the closed-box section. Flutter occur before aerostatic instability at initial attack angle of $+3^{\circ}$ and $0^{\circ}$, while the aerostatic torsional divergence occur before flutter at initial attack angle of $-3^{\circ}$. The twin-box section is the best in terms of both aerostatic and flutter stability among those bridge decks. Then mechanisms of aerostatic torsional divergence are revealed by tracking the cable forces synchronous with deformation of the bridge decksin the instability process. It was also found that the onset wind velocities of these bridge decks are very similar at attack angle of $-3^{\circ}$. This indicatesthat a stable triangular structure made up of the cable planes, the tower, and the bridge deck greatly improves the aerostatic stability of the structure, while the aerodynamic effects associated with the aerodynamic configurations of the bridge decks have little effects on the aerostatic stability at initial attack angle of $-3^{\circ}$. In addition, instability patterns of the bridge depend on both the initial attack angles and aerodynamic configurations of the bridge decks. This study is helpful in determining bridge decksfor super long-span bridges in future.

• Wind and Structures
• /
• 제4권5호
• /
• pp.367-382
• /
• 2001

Wind tunnel tests were conducted on a model of deck section from the Ting Kau cable stayed bridge. The purpose of the tests was to determine the set of aerodynamic derivatives conventionally used to describe the motion-induced forces arising from the wind flow, and to investigate the stability of the deck under different conditions of turbulence and angle of attack. The study shows that except for large negative angles of attack the deck section itself is stable up to a high wind speed, and that when instability does occur it is essentially a single degree of freedom (torsional) flutter.

• Wind and Structures
• /
• 제30권6호
• /
• pp.547-558
• /
• 2020

With the development of economy and construction technology, more and more bridges are built in complex mountainous areas. Accurate assessment of wind parameters is important in bridge construction at complex terrain. In order to investigate the wind characteristics in the high-altitude difference area, a complex mountain terrain model with the scale of 1:2000 was built. By using the method of wind tunnel tests, the study of wind characteristics including mean wind characteristics and turbulence characteristics was carried out. The results show: The wind direction is affected significant by the topography, the dominant wind direction is usually parallel to the river. Due to the sheltering effect of the mountain near the bridge, the wind speed and wind attack angle along the bridge are both uneven which is different from that at flat terrain. In addition, different from flat terrain, the wind attack angle is mostly negative. The wind profiles obey exponential law and logarithmic law. And the fitting coefficient is consistent with the code which means that it is feasible to use the method of wind tunnel test to simulate complex terrain. As for turbulence characteristics, the turbulence intensity is also related to the topography. Increases sheltering effect of mountain increases the degree of breaking up the large-scale vortices, thereby increasing the turbulence intensity. Also, the value of turbulence intensity ratio is different from the recommended values in the code. The conclusions of this study can provide basis for further wind resistance design of the bridge.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2011년 춘계학술대회논문집
• /
• pp.434-440
• /
• 2011

Oscillating airfoil haw been challenged for the dynamic stalls of airfoil am wind turbines at high angle of attach. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance am safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed for the oscillating airfoil at high angle of attack around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.2 and Reynolds number of $1.2{\times}10^4$. The lift, drag, pressure distribution, etc. are analyzed according to the pitching oscillation. Unsteady velocity field, periodic vortex shedding, the unsteady pressure distribution, and the acoustic fields are analyzed. The effects of these unsteady characteristics in the aerodynamic coefficients are analyzed.

• Wind and Structures
• /
• 제13권2호
• /
• pp.127-144
• /
• 2010

Pressure measurements on static and autorotating flat plates have been recently reported by Lin et al. (2006), Holmes, et al. (2006), and Richards, et al. (2008), amongst others. In general, the variation of the normal force with respect to the angle of attack appears to stall in the mid attack angle range with a large scale separation in the wake. To date however, no surface pressures have been measured on auto-rotating plates that are typical of a certain class of debris. This paper presents the results of an experiment to measure the aerodynamic forces on a flat plate held stationary at different angles to the flow and allowing the plate to auto-rotate. The forces were determined through the measurement of differential pressures on either side of the plate with internally mounted pressure transducers and data logging systems. Results are presented for surface pressure distributions and overall integrated forces and moments on the plates in coefficient form. Computed static force coefficients show the stall effect at the mid range angle of attack and some variation for different Reynolds numbers. Normal forces determined from autorotational experiments are higher than the static values at most pitch angles over a cycle. The resulting moment coefficient does not compare well with current analytical formulations which suggest the existence of a flow mechanism that cannot be completely described through static tests.

• Wind and Structures
• /
• 제35권1호
• /
• pp.67-81
• /
• 2022

While the aerodynamics of solid bluff bodies is reasonably well-understood and methodologies for their reliable numerical simulation are available, the aerodynamics of porous bluff bodies formed by assembling perforated plates has received less attention. The topic is nevertheless of great technical interest, due to their ubiquitous presence in applications (fences, windbreaks and double skin facades to name a few). This work follows previous investigations by the authors, aimed at verifying the consistency of numerical simulations based on the explicit modelling of the perforated plates geometry and their representation by means of pressure-jumps. In this work we further expand such investigations and, contextually, we provide insight into the flow arrangement and its sensitivity to important modelling and setup configurations. To this purpose, Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Large-Eddy Simulations (LES) are performed for a 5:1 rectangular cylinder at null angle of attack. Then, using URANS, porosity and attack angle are simultaneously varied. To the authors' knowledge this is the first time in which LES are used to model a porous bluff body and compare results obtained using the explicit modelling approach to those obtained relying on pressure-jumps. Despite the flow organization often shows noticeable differences, good agreement is found between the two modelling strategies in terms of drag force.

• 대한공업교육학회지
• /
• 제32권1호
• /
• pp.117-133
• /
• 2007

이 연구는 중등학교 학생들에게 비행의 원리를 이해하고 항공 기술 분야에 흥미를 가질 수 있도록 하기 위해 학교 현장에 적용 가능한 교수-학습 자료인 학습용 풍동의 힘 측정 장치를 개발하였다. 연구의 내용은 학습용 풍동의 힘 측정 장치 개발과 실험으로 이루어져 있다. 이 연구에서 얻은 주요 결과를 정리하면 다음과 같다. 공과대학 기계계열 학과나 항공연구소 등에서 사용하는 고가의 Load cell을 이용한 장치 대신에 지렛대 원리를 활용한 간단한 구조이다. 종합된 하나의 장치로 양력, 항력 및 유체 저항 비교 실험이 가능하다. 에어포일 받음각에 따른 양력 계수는 실험값과 이론값이 전체적으로 비슷한 경향성을 갖으며, 실속 현상은 실험값이 이론값보다 더 큰 받음각에서 나타났다. 에어포일 받음각에 따른 항력 계수는 실험값과 이론값이 전체적으로 비슷한 경향성을 갖으며, 실험값은 이론값에 비해 항력 계수의 증가 비율이 완만하게 증가하였다.