• Title/Summary/Keyword: stall delay

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Effect of stall delay characteristics of symmetrical aerofoil using lateral circular ridges

  • Raatan, V.S.;Ramaswami, S.;Mano, S.;Pillai, S. Nadaraja
    • Wind and Structures
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    • v.34 no.4
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    • pp.385-394
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    • 2022
  • Global Warming has been driven majorly by the consumption of fossil fuels. Harnessing energy from wind is viable solution towards reducing carbon footprint created due to burning such fuels, However, wind turbines have their problems of flow separation and aerodynamic stall to tackle with. In an attempt to delay the stall angle and improve the aerodynamic characteristics of the NACA 0015 symmetrical aerofoil, lateral cylindrical ridges were attached to its suction surface, at chord positions ranging from 0.1c to 0.5c. The characteristics of the original and ridged aerofoils were obtained using simultaneous pressure readings taken in a wind tunnel, at a free stream Reynolds number of Re = 2.81 × 105 for a wide range of free stream angles of attack ranging from -45° to 45°. Depending on the ridge size, a delay in stall angle varying from 5° to 20° was achieved together with the maximum increase in lift in the post-stall phases. Additionally, efforts were made to identify the optimum position for each ridge.

Thrust Generation on Flapping-Aifoil by Dynamic Stall (동적 실속을 이용한 Flapping-Airfoil의 추력 발생)

  • Lee Jung Sang;Kim Chongam;Rho Oh-Hyun
    • 한국전산유체공학회:학술대회논문집
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    • 2002.10a
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    • pp.35-40
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    • 2002
  • This paper deals with a thrust generation on flapping-airfoil by dynamic stall. Dynamic stall refers to a series of complicated aerodynamic phenomena accompanied by a stall delay in unsteady motion. In most cases, once it occurs, the dynamic stall may lead to an abrupt fluctuation of aerodynamic forces. An inverse $k\acute{a}rm\acute{a}n$ vortex has been considered as a main reason for a thrust generation. In this paper, however, we have found out that a thrust is closely related to reduced frequency and leading edge vortex in addition to inverse Karman vortex. In order to certify our opinion, picking and plunging motions were calculated with the parameter of amplitude and frequency by using the unsteady, incompressible Navier-Stokes flow solver with a two-equation turbulence model. For more efficient computation, it is parallelized by MPI programming method.

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Flow Characteristics of a Paraglider Canopy with Leading-edge Tubercles (선단돌기가 적용된 패러글라이더 캐노피의 유동특성 연구)

  • Shin, Jeonghan;Chae, Seokbong;Shin, Yisu;Park, Jungmok;Song, Ginseok;Kim, Jooha
    • Journal of the Korean Society of Visualization
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    • v.19 no.3
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    • pp.106-114
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    • 2021
  • In the present study, we investigate the flow characteristics of a paraglider canopy with leading-edge tubercles by performing force measurement and surface flow visualizations. The experiment is conducted at Re = 3.3×105 in a wind tunnel, where Re is the Reynolds number based on the mean chord length and the free-stream velocity. The canopy model with leading-edge tubercles has flow characteristics of a two-step stall, showing an earlier onset of the first stall than the canopy model without leading-edge tubercles. However, the main stall angle of the tubercled model is much larger than that of the canopy model without tubercles, resulting in a higher aerodynamic performance at high angles of attack. The delay in the main stall is ascribed to the suppression of separation bubble collapse around the wingtip at high angles of attack.

Application of stall delay model to wind turbine blade (블레이드 성능예측을 위한 실속지연 모델 적용)

  • Shin, Hyung-Ki;Park, Ji-Woong;Kim, Ho-Geon;Lee, Soo-Gab;Kim, Seok-Woo
    • 한국신재생에너지학회:학술대회논문집
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    • 2006.11a
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    • pp.253-256
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    • 2006
  • BEMT나 wake method와 같이 2-D 에어포일의 데이터를 성능과 하중 해석에 이용하는 기법의 경우 에어포일 데이터의 정확도는 전체 결과에 큰 영향을 미친다. 풍력 블레이드와 같은 회정익에서는 2-D 에어포일 데이터를 실험 등을 통하여 정확히 얻어서 적용 시키더라도 예측 결과는 실제값과 큰 차이를 보이는 경우가 많다. 이는 회전익의 유동 특성에 의해 발생하는 실속 지연의 효과로 인한 것이며 이것은 입력에 사용되는 에어포일 데이터에는 반영되지 않으므로 자체적인 보정이 필요하다. 본 연구에서는 이러한 문제를 해결하기 위해 현재 제시되어 있는 실속 지연 모델을 살펴보고 이를 불레이드의 성능과 하중 해석에 저용시켜 보아 그 유효성에 대하여 살펴보았다.

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Numerical Analysis of Stall Characteristics for Turboprop Aircraft (터보프롭 항공기의 실속 특성 수치해석)

  • Park, Young Min;Chung, Jin Deog
    • Aerospace Engineering and Technology
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    • v.11 no.2
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    • pp.65-72
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    • 2012
  • Numerical simulations were performed to study the stall characteristics of turboprop aircraft. Stall characteristics were qualitatively investigated using the computational results of various configurations based on the combinations of propeller and high lift device. For the analysis of stall characteristics, three-dimensional Navier-Stokes solver with Spalart-Allmaras turbulence model was used and the relative motion between propeller and wing was simulated using sliding mesh technique. For the cruise configurations, major flow separation was occurred at the fuselage/wing fairing and the separation was reduced under propeller slipstream condition. For the high lift device configuration without propeller, major flow separation was occurred at the outboard side of nacelle. With rotating propeller, early stall onset due to low relative velocity and high effective angle of attack was observed on the outboard wing section. Regarding rotating direction of propeller, inboard-down direction was preferred due to the stall delay effect of propeller slipstream.

An Analysis of Delayed Voltage Recovery Phenomenon according to the Characteristics of Motor Load in Korean Power System (모터부하 특성에 따른 국내 전력계통의 전압 지연 회복 현상 분석)

  • Lee, Yun-Hwan
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.65 no.3
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    • pp.178-182
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    • 2016
  • FIDVR(Fault Induced Delayed Voltage Recovery) is a phenomenon that recovery of the system voltage level delays after the fault. Cause of FIDVR phenomenon is motor load characteristic about voltage and reactive power. In low voltage condition, the motor go to stall state that consume large amount of reactive power. As a result, the voltage recovery problem is that of repeated occurrences of sustained low voltage following faults on the system. In this paper, analysis the characteristics of the motor load. And using the korean power system actual data, perform a case studies to voltage delay recovery phenomenon alleviation method. Change of each parameters by analyzing the effect on system and selecting an influence parameter. In addition, dynamic characteristic analysis of the resulting difference in the proportion by the motor load in power systems, considering the effect on the voltage stability.

Effect of trailing-edge modification over aerodynamic characteristics of NACA 0020 airfoil

  • Ethiraj, Livya;Pillai, Subramania Nadaraja
    • Wind and Structures
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    • v.33 no.6
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    • pp.463-470
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    • 2021
  • This study investigates the aerodynamic characteristics of NACA series airfoil by altering the trailing edge in the form of extended and serrated sections. This contemporary advent examined NACA 0020 airfoil experimentally at the angle of attack ranging from 0° to 45° and for the Reynolds number of 2.46 × 105. To figure out the flow behaviour, the standard average pressure distribution over the airfoil surface is estimated with 50 pressure taps. The time series surface pressure is recorded for 700 Hz of sampling frequency. The extended trailing edge of 0.1 c, 0.2 c and 0.3 c are attached to the base airfoil. Further, the triangular serration is introduced with the base length of 2 cm, 4 cm and 6 cm. Each base length with three different amplitudes of 0.1 c, 0.2 c and 0.3 c were designed and equipped with the baseline case at the trailing edge and tested. The aerodynamic force coefficient, as well as pressure coefficient are presented. The obtained data advises that modification in the trailing edge will reflect the aerodynamic characteristics and the flow behaviour over the section of a wing. Resultantly, the extended trailing edge as a thin elongated surface attached to a base airfoil without revising the main airfoil favors good lift increment. The serrated trailing edge acts as a flow control device by altering the flow pattern results to delay the stall phenomenon. Besides it, improves lift co-efficient with less amount of additional drag. This extended and serrated trailing edge approach can support for designing the future smart airfoil.

Numerical analysis of the effect of V-angle on flying wing aerodynamics

  • Zahir Amine;Omer Elsayed
    • Advances in aircraft and spacecraft science
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    • v.10 no.2
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    • pp.141-158
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    • 2023
  • In current research work, the aerodynamics performance of a newly designed large flying V aircraft is numerically investigated. Three Flying V configurations, with V-angles of 50°, 70° and 90° that represent the minimum, moderate, and maximum configurations respectively, were designed and modeled to assess their aerodynamic performance at cruise flight conditions. The unstructured mesh was developed using ICEM CFD and Ansys-Fluent was used as an aerodynamic solver. The developed models were numerically simulated at cruise flight conditions with a Mach number equal to 0.15. K-ω SST turbulence model was chosen to account for flow turbulence.The authors performed steady flow simulations.The results obtained from the experimentation reveal that the maximum main angle configuration of 90° had the highest CLmax value of 0.46 compared to other configurations. While the drag coefficient remained the same for all three configurations, the 50° V-angle configuration achieved the maximum stall angle of 35°. With limited stall delay benefits, the flying V possesses no sufficient stability, due to the flow separation detected at whole elevon and winglet suction side areas at AoA equal and higher than 30°.

New Free Wake Method Development for Unsteady Aerodynamic Load on HAWT Blade and Experimental Analysis (풍력블레이드 비정상 공력하중 해석을 위한 자유후류기법 개발 및 실험적 연구)

  • Shin Hyungki;Park Jiwoong;Kim Hogeon;Lee Soogab
    • 한국신재생에너지학회:학술대회논문집
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    • 2005.06a
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    • pp.33-36
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    • 2005
  • A critical issue in the field of the rotor aerodynamics is the treatment of the wake. The wake is of primary importance in determining overall aerodynamic behavior, especially, a wind turbine blade includes the unsteady air loads problem. In this study, the wake generated by blades are depicted by a free wake model to analyse unsteady loading on blade and a new free wake model named Finite Vortex Element(FVE hereafter) is devised in order to include a wake-tower interact ion. In this new free wake model, blade-wake-tower interaction is described by cutting a vortex filament when the filament collides with a tower. This FVE model is compared with a conventional free wake model and verified by a comparison with NREL and SNU wind tunnel model. A comparison with NREL and SNU data shows validity and effectiveness of devised FVE free wake model and an efficient.

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Development of a new free wake model considering a waketower interaction for a horizontal axis wind turbine (후류와 타워의 영향을 고려한 수평축 풍력발전기 블레이드의 비정상 하중 예측을 위한 새로운 자유후류기법의 연구)

  • Shin Hyungki;Park Jiwoong;Lee Soongab;Kim Jueon
    • New & Renewable Energy
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    • v.1 no.1 s.1
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    • pp.54-63
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    • 2005
  • A critical issue in the field of the rotor aerodynamics is the treatment of the wake. The wake is of primary importance in determining overall aerodynamic behavior, especially, a wind turbine blade includes the unsteady airloads problem. In this study, the wake generated by blades are depicted by a free wake model to analyse unsteady loading on blade and a new free wake model named Finite Vortex Element(FVE hereafter) is devised in order to include a wake-tower interaction. In this new free wake model, blade-wake-tower interaction is described by cutting a vortex filament when the filament collides with a tower. This FVE model is compared with a conventional free wake model and verified by a comparison with NRELand SNU wind tunnel model. A comparison with NREL and SNU data shows validity and effectiveness of devised FVE free wake model and an efficient.

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