• Title/Summary/Keyword: Flow attack angle

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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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    • 2009.11a
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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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The Variation of Flow Field and Hydrodynamic Coefficients of Submarine by Changes of Angle of Attack and Yaw Angle (유동 방향 변화에 따른 잠수함 주위의 유동 특성과 유체동역학적 계수의 변화)

  • Jang Jin-Ho;Park Warn-Gyu
    • Journal of the Society of Naval Architects of Korea
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    • v.43 no.4 s.148
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    • pp.460-466
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    • 2006
  • The three-dimensional RANS equations were applied to analyze the flow field of a submarine. To validate the code, the DARPA SUBOFF bare hull and an eliipsoid at angles of attack of $10^{\circ}\;and\;30^{\circ}$ were simulated and good agreement with experiments was obtained. After the code validation, the flows over the full configuration of DARPA SUBOFF model having a fairwater and four stern appendages were simulated at four angles of attack $(0^{\circ},\;10^{\circ},\;20^{\circ},\;30^{\circ})$ and three yaw angles $(10^{\circ},\;20^{\circ},\;30^{\circ})$ Specifically, the pressure contours and streamlines of fairwater and stern appendage were compared as the angle of attack and yaw angle changed. The variations of hydrodynamic forces were also calculated.

Unsteady galloping of sharp-edged bluff bodies: experimental observations on the effect of the wind angle of attack

  • Chen, Cong;Dai, Bingyu;Wieczorek, Niccolo;Unglaub, Julian;Thiele, Klaus
    • Wind and Structures
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    • v.35 no.4
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    • pp.255-268
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    • 2022
  • Light-weight or low-damped structures may encounter the unsteady galloping instability that occurs at low reduced wind speeds, where the classical quasi-steady assumption is invalid. Although this unsteady phenomenon has been widely studied for rectangular cross sections with one side perpendicular to the incidence flow, the effect of the mean wind angle of attack has not been paid enough attention yet. With four sectional models of different side ratios and geometric shapes, the presented research focuses on the effect of the wind angle of attack on unsteady galloping instability. In static tests, comparatively strong vortex shedding force was noticed in the middle of the range of flow incidence where the lift coefficient shows a negative slope. In aeroelastic tests with a low Scruton number, the typical unsteady galloping, which is due to an interaction with vortex-induced vibration and results in unrestricted oscillation initiating at the Kármán vortex resonance wind speed, was observed for the wind angles of attack that characterize relatively strong vortex shedding force. In contrast, for the wind angles of attack with relatively weak shedding force, an "atypical" unsteady galloping was found to occur at a reduced wind speed clearly higher than the Kármán-vortex resonance one. These observations are valid for all four wind tunnel models. One of the wind tunnel models (with a bridge deck cross section) was also tested in a turbulent flow with an intensity about 9%, showing only the atypical unsteady galloping. However, the wind angle of attack with the comparatively strong vortex shedding force remains the most unfavorable one with respect to the instability threshold in low Scruton number conditions.

Flow Characteristics around a NACA0012 Airfoil by PIV (PIV에 의한 NACA0012 익 주변의 유동특성)

  • Choi, M.S.;Cho, D.H.;Lee, Y.H.
    • Journal of Power System Engineering
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    • v.3 no.1
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    • pp.29-37
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    • 1999
  • The flow characteristics of a NACA0012 airfoil was investigated in rectangular water circulating channel. The flow patterns around an airfoil at various angles of attack between $0^{\circ}\;and\;30^{\circ}\;at\;Re=1.91{\times}104$ were visualized and measured with 2-D PIV system and laser sheet illumination. Flow behaviors such as velocity distribution, kinetic energy and flow separation etc. around an airfoil were obtained by means of 2-D PIV system. The behaviors show the difference of flow pattern clearly and separation phenomena become more active with increasing angle of attack.

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A Study on Flow Induced Vibration of Cantilever Plate with Angle of Attack (받음각을 갖는 평판보의 유동 여기진동에 관한 연구)

  • 이기백;손창민;김봉환
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.6
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    • pp.1919-1932
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    • 1991
  • Experimental studies are conducted to investigate the Flow-Induced Vibration mechanism for cantilever plate model with the angle of attack (.alpha.=10.deg., 20.deg., 30.deg.). Research is divided into two parts. First, the flow fields around two dimensional flat plate model are investigated using LDV system. Second, the vortex shedding frequency and response spectra of cantilever plate are obtained experimentally using gap sensor and hot wire anemometer. Finite element method program was used in order to predict the flow field and pressure field around thin flat plate. And some predicted results were compared with the experimental data. The aspect ration of test model is d/t=25 (d; width, t; thickness). From the measurement of the flow field it was found that in the case of small inclined (.alpha.=10.deg., 20.deg.) relatively, the separated boundary layer at sharp leading edge developed smoothly downstream. With increasing the angle of attack of the plate, stagnation region was appeared on the back side of the plate and separated boundary layer was extended downstream. These trends are a good agreement with the computational results. It was found by analysis of response spectra of cantilever plate that the influences of vortex shedding frequency were important at the large of attack (.alpha.=30.deg.), and two peak values appear in entire test model at 24Hz, 150Hz.

Interaction between Turbulent Boundary Layer and Wake behind an Elliptic Cylinder at Incidence (앙각을 가진 타원형 실린더 후류와 평판 경계층의 상호작용에 대한 연구)

  • Choi, Jae-Ho;Lee, Sang-Joon
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.465-471
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    • 2000
  • The flow characteristics around an elliptic cylinder with axis ratio of AR=2 located near a flat plate were investigated experimentally to study the interaction between the cylinder wake and the turbulent boundary layer. The pressure distributions on the cylinder surface and on the flat plate were measured with varying the angle of attack of the cylinder. In addition, the velocity profiles of wake behind the cylinder were measured using a hot-wire anemometry As the angle of attack increases, the location of peak pressure on the windward and leeward surfaces of the cylinder moves toward the rear and front of the cylinder, respectively. At positive angles of attack, the position of the minimum pressure on the flat plate surface is moved downstream, but it is moved upstream at negative angles of attack. With increasing the angle of attack, the vortex shedding frequency is gradually decreased and the critical angel of attack exists in terms of the gap ratio. By installing the elliptic cylinder at negative angle of attack, the turbulent boundary layer over the flat plate is disturbed more than that at positive incidence. This may be attributed to the shift of separation point on the lower surface of the cylinder according to the direction of the angle of attack.

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Vortex Interaction Characteristics of a Delta Wing/LEX (삼각날개/LEX에서의 와류 상호작용 특성)

  • 이기영;손명환
    • Journal of the Korea Institute of Military Science and Technology
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    • v.5 no.3
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    • pp.77-86
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    • 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.

Interaction between Turbulent Boundary Layer and Wake Behind an Elliptic Cylinder at Incidence (앙각을 가진 타원형 실린더 후류와 평판경계층의 상호작용에 대한 연구)

  • Choi, Jae-Ho;Lee, Sang-Joon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.7
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    • pp.976-983
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    • 2000
  • The flow characteristics around an elliptic cylinder with axis ratio of AR=2 located near a flat plate were investigated experimentally to study the interaction between the cylinder wake and the turbulent boundary layer. The pressure distributions on the cylinder surface and on the flat plate were measured with varying the angle of attack of the cylinder. In addition, the velocity profiles of wake behind the cylinder were measured using a hot-wire anemometry As the angle of attack increases, the location of peak pressure on the windward and leeward surfaces of the cylinder moves toward the rear and front of the cylinder, respectively. At positive angles of attack, the position of the minimum pressure on the flat plate surface is moved downstream, but it is moved upstream at negative angles of attack. With increasing the angle of attack, the vortex shedding frequency is gradually decreased and the critical angle of attack exists in terms of the gap ratio. By installing the elliptic cylinder at negative angle of attack, the turbulent boundary layer over the flat plate is disturbed more than that at positive incidence. This may be attributed to the shift of separation point on the lower surface of the cylinder due to the presence of a ground plate nearby.

Heat Transfer and Frictions in the Convergent/divergent Channel with Λ/V-shaped Ribs on Two Walls

  • Kim, Beom-soo;Lee, Myung-sung;Ahn, Soo-whan
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.3
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    • pp.395-402
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    • 2017
  • The local heat transfer and total pressure drops of developed turbulent flows in the ribbed rectangular convergent/divergent channels with ${\Lambda}/V-shaped$ ribs have been investigated experimentally. The channels have the exit hydraulic diameter ($D_{ho}$) to inlet hydraulic diameter ($D_{hi}$) ratios of 0.67 for convergence and 1.49 for divergence, respectively. The ${\Lambda}/V-shaped$ ribs with three different flow attack angles of $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$ are manufactured with a fixed rib height (e) of 10 mm and the ratio of rib spacing (S) to height (e) of 10 on the walls. Thermal performances of the ribbed rectangular convergent/divergent channels are compared with the smooth straight tube under identical pumping power. The results show that the flow attack angle of $45^{\circ}$ with ${\Lambda}-shaped$ rib has the greatest thermal performance at all the Reynolds numbers studied in the convergent channel; whereas, the flow attack angle of $60^{\circ}$ with V-shaped rib has the greatest thermal performance over Reynolds number of 30,000 in the divergent channel.

A Study of the Flow Pattern and the PIV Analysis around a Flap Foil (플랩을 갖는 익 주변의 유동 특성과 PIV 해석에 관한 연구)

  • Choi, Hee-Jong;Lee, Gyoung-Woo;Oh, Kyoung-Gun;Jo, Dae-Hwan;Lee, Seung-Keon
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • v.29 no.1
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    • pp.35-40
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    • 2005
  • Maneuverability of ships has been receiving a great deal of attention both concerning navigation safety and the prediction of ship maneuvering characteristics, to improve it. high-lift device could be applied to design of rudder at design stage. Now, we carried out the flow visualization and investigation of flow field around a flap rudder(trailing-edge flap). Flow visualization results of flap defection shown as the flow around a NACA0020 Flap Rudder will be conducted in a Circulating Water Channel. The purpose of this investigation will be to investigate the development of the separation region on the flap rudder with the variation of the angle of attack and determine the angle of attack at which the flow separates and reattaches.

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