• Title, Summary, Keyword: wind attack-angle

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Full-scale study of conical vortices and roof corner pressures

  • Wu, F.;Sarkar, P.P.;Mehta, K.C.
    • Wind and Structures
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    • v.4 no.2
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    • pp.131-146
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    • 2001
  • A full-scale synchronized data acquisition system was set up on the roof of the experimental building at the Texas Tech University Wind Engineering Research Field Laboratory to simultaneously collect approaching wind data, conical vortex images, and roof corner suction pressure data. One-second conditional sampling technique has been applied in the data analysis, which makes it possible to separately evaluate the influencing effects of the horizontal wind angle of attack, ${\theta}$, and the vertical wind angle of attack, ${\varphi}$. Results show a clear cause-and-effect relationship between the incident wind, conical vortices, and the induced roof-corner high-suction pressures. The horizontal wind angle of attack, ${\theta}$, is shown to be the most significant factor in influencing the overall vortex structure and the suction pressures beneath. It is further revealed that the vertical wind angle of attack, ${\varphi}$, plays a critical role in generating the instantaneous peak suction pressures near the roof corner.

Non-uniform wind environment in mountainous terrain and aerostatic stability of a bridge

  • Chen, Xingyu;Guo, Junjie;Tang, Haojun;Li, Yongle;Wang, Lei
    • Wind and Structures
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    • v.30 no.6
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    • pp.649-662
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    • 2020
  • The existence of a dam has potential effects on the surrounding wind environment especially when it is located in mountainous areas. In this situation, the long-span bridge over the reservoir can easily be exposed to non-uniform incoming flows, affecting its wind-resistance performance. This paper presents a study on the aerostatic stability of such a bridge. Wind tunnel tests were first carried out to investigate the wind environment above a mountainous reservoir. The results show that the angle of attack and the wind speed along the bridge axis show obvious non-uniform characteristics, which is related to the inflow direction. When winds come from the south where the river is winding, the angle of attack varies along the span direction significantly. The finite element model for the bridge was established using ANSYS software, and effects of non-uniform wind loads on the aerostatic stability were computed. Non-uniform angle of attack and wind speed are unfavorable to the aerostatic stability of the bridge, especially the former. When the combined action of non-uniform angle of attack and wind speed is considered, the critical wind speed of aerostatic instability is further reduced. Moreover, the aerostatic stability of the bridge is closely related to the dam height.

Study for Dynamic Stall Characteristics of Vertical Axis Wind Turbine Airfoil (수직형 풍력터빈 익형의 동특성 분석)

  • Kim, Cheol-Wan;Cho, Tae-Whan
    • 한국신재생에너지학회:학술대회논문집
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    • pp.478-481
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    • 2009
  • As a first step for aerodynamic analysis of vertical axis wind turbine, dynamic stall characteristics of airfoil was investigated. Dynamic stall of wind turbine airfoil is caused by severe variation of angle of attack and relative velocity of flow around airfoil. Angle of attack and relative velocity can be expressed with tip speed ratio. Variation of angle of attack is strongly dependent on the tip speed ratio. For tip speed ratio, 1.4 and free stream velocity, 15m/s, dynamic stall characteristics of wind turbine airfoil is compared with those of oscillating airfoil having same angle of attack variation.

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Wind Tunnel Test of Aerodynamic Forces and Wind Pressures Acting on Muilti-layer Radom in Active Phased Array Radar (풍동실험을 통한 능동위상배열레이더에서 다층레이돔에 작용하는 공기력과 풍압의 실험적 연구)

  • Yim, Sung-Hwan;Kang, Kwang-Hee;Choi, Ji-Ho;Lee, Seung-Ho;Kwon, Soon-Duck
    • Journal of the Korea Institute of Military Science and Technology
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    • v.17 no.1
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    • pp.149-157
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    • 2014
  • In this paper, we investigated the sensitivity of aerostatic force coefficients of multi-layer radom in the various wind speeds. The test was conducted in KOCED Wind Tunnel Center in Chonbuk National University, and wind speeds were in the range from 5 m/s to 26 m/s in order to determine the Reynolds number independence. The test results of present multi-layer radom were not affected by the Reynolds number, The maximum positive pressure coefficient was found to be 1.08 at the center of the front of the plane in angle of attack of 0 degree, the maximum negative pressure coefficient was -2.03 at the upper right corner in angle of attack of 120 degree, while maximum drag coefficient was 1.11 in angle of attack of 180 degree.

An Experimental Study on High Angle of Attack Static Stability Analysis For the Aerodynamic Design of Canard Type High Maneuver Aircraft (카나드 형상 고시동 항공기 공력설계를 우한 높은 받음각 정적 안정성 분석 실험 연구)

  • Chung, In-Jae
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.7
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    • pp.575-580
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    • 2007
  • During the conceptual design phase of a canard type high maneuverable aircraft, the low speed small scale wind tunnel test was conducted to investigate the high angle-of-attack static stability of the aircraft. In this study, 1/50th scale generic canard-body-wing model was used for the small scale wind tunnel test. For the analysis of static stability including high angle-of-attack nonlinear characteristics, the vertical tail effects were studied due to canard deflections. In addition, the nose chine effects were studied at high angle-of-attack. Based on the results obtained from the experimental study, the configuration change effects for canard type aircraft on high angle-of-attack static stability have been able to analyze.

Flow past a Square Cylinder with an Angle of Attack (기울어진 정방형 실린더에 작용하는 유체력)

  • Yoon, Dong-Hyeog;Yang, Kyung-Soo;Choi, Choon-Bum
    • Proceedings of the KSME Conference
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    • pp.2754-2758
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    • 2008
  • Numerical investigation has been carried out for laminar flow ($Re{\leq}150$) past a square cylinder in cross freestream with an angle of attack. This study would be the first step towards understanding flow-induced forces on cylindrical structures under a strong gust of wind from the viewpoint of wind hazards. Collecting all the numerical results obtained, we propose contour diagrams of drag/lift coefficients and Strouhal number (St) on an Re-Angle plane.

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Flow Characteristics around Archimedes Wind Turbine according to the Change of Angle of Attack (받음각 변화에 따른 아르키메데스 풍력발전 날개 주위의 유동장 변화)

  • Li, Qiang;Kim, Hyun Dong;Ji, Ho Seong;Kim, Kyung Chun
    • Journal of the Korean Society of Visualization
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    • v.11 no.1
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    • pp.28-33
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    • 2013
  • This paper describes aerodynamic characteristics of an Archimedes spiral wind turbine with various angles of attack. The range of angles was controlled from $-30^{\circ}$ (clockwise) to $+30^{\circ}$ (clockwise). The rotating speed of wind turbine at the same angle of attack in both directions was different. The reason why the-maximum rotational speed was observed at $15^{\circ}$ in clockwise direction can be explained based on angular momentum conservation. Quantitative flow visualization around Archimedes wind turbine blade was carried out between $-15^{\circ}$ (clockwise) and $+15^{\circ}$ (counter clockwise) using high resolution PIV method. The relationship between drag force and rotating speeds was discussed. From these results, optimum design on yawing system of Archimedes spiral wind turbine may provide high efficiency on small wind power system.

Flutter performance of central-slotted plate at large angles of attack

  • Tang, Haojun;Li, Yongle;Chen, Xinzhong;Shum, K.M.;Liao, Haili
    • Wind and Structures
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    • v.24 no.5
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    • pp.447-464
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    • 2017
  • The flutter instability is one of the most important themes need to be carefully investigated in the design of long-span bridges. This study takes the central-slotted ideal thin flat plate as an object, and examines the characteristics of unsteady surface pressures of stationary and vibrating cross sections based on computational fluid dynamics (CFD) simulations. The flutter derivatives are extracted from the surface pressure distribution and the critical flutter wind speed of a long span suspension bridge is then calculated. The influences of angle of attack and the slot ratio on the flutter performance of central-slotted plate are investigated. The results show that the critical flutter wind speed reduces with increase in angle of attack. At lower angles of attack where the plate shows the characteristics of a streamlined cross-section, the existence of central slot can improve the critical flutter wind speed. On the other hand, at larger angles of attack, where the plate becomes a bluff body, the existence of central slot further reduces the flutter performance.

Effects of corner cuts and angles of attack on the Strouhal number of rectangular cylinders

  • Choi, Chang-Koon;Kwon, Dae-Kun
    • Wind and Structures
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    • v.6 no.2
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    • pp.127-140
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    • 2003
  • An investigation into the effect of corner cuts on the Strouhal number of rectangular cylinders with various dimensional ratios and various angles of attack is described. The Strouhal number given as a function of corner cut size is obtained directly from the aerodynamic behavior of the body in a uniform flow through a series of wind-induced vibration tests. For a quick verification of the validity of the Strouhal numbers obtained in this way, they are compared with the approximated the Strouhal numbers based on Shiraishi's early research. The test results show that the Strouhal number of the model with various corner cuts has a fluctuating trend as the angle of attack changes. For each cutting ratio as the angle of attack increases at each cutting ratio above $15^{\circ}$, the Strouhal number decreases gradually, and these trends are more evident for larger corner cut sizes. However, a certain corner cut size which is effective in reducing the wind-induced vibration can be identified by larger Strouhal numbers than those of other corner cut sizes. Three distinct characteristics of Strouhal number variation can be identified in three regions which are termed as Region I, II, and III based on the general trend of the test results. It is also found that the corner cut is effective in one region (Region-II) and less effective in another one (Region-III) when only the vortex-induced vibration occurs.

Development of Servo Type Angle-of-Attack Sensor for UAV (무인항공기용 서보형 받음각센서 개발)

  • Park, Mi-Hyun;Kim, Sung-Su;Ryoo, Chang-Kyung;Choi, Kee-Young;Park, Choon-Bae
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.5
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    • pp.511-517
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    • 2009
  • A servo type angle of attack sensor using the null-seeking method is designed and its characteristics are analyzed in this study. Angle-of-attack in the null-seeking method is given by the probe rotation angle with respect to the body reference line when pressure difference measured in two holes on the probe becomes zero. This method provides highly accurate and uniform angle-of-attack measurements over all range. Hence, this kind of angle-of-attack sensor is adequate for unmanned aerial vehicles(UAVs). In this paper, we first analyze the requirements for developing angle-of-attack sensors. And the servo type angle-of-attack sensor is then designed and fabricated. The on-board angle-of-attack calculation algorithm is also developed. Finally, the characteristics of the developed angle-of-attack sensor are identified through MATLAB Simulink and wind tunnel tests.