Investigation of dynamic stall onset

Geißler, W.; Haselmeyer, Hartmut

doi:10.1016/j.ast.2006.05.001

Cited by 44 publications

(23 citation statements)

References 9 publications

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“…The concept at first might appear similar to Vortex-Induced-Vibration (VIV) of elastically mounted cylinders [55,56] and can be perceived to cause structural issues for a turbine blade. However, the upstream cylindrical wire in the current case is less than 1%c and, therefore, the shed vorticity is approximately of a similar scale as the boundary layer thickness during the dynamic stall process [57]. Such an arrangement will, hence, not induce the large-scale vibrations that are conventionally observed during the VIV process.…”

Section: Elevated Wirementioning

confidence: 93%

Methods to control dynamic stall for wind turbine applications

2016

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a b s t r a c tDynamic stall (DS) on a wind turbine is encountered when the sectional angles of attack of the blade rapidly exceeds the steady-state stall angle of attack due to in-flow turbulence, gusts and yawmisalignment. The process is considered as a primary source of unsteady loads on wind turbine blades and negatively influences the performance and fatigue life of a turbine. In the present article, the control requirements for DS have been outlined for wind turbines based on an in-depth analysis of the process. Three passive control methodologies have been investigated for dynamic stall control: (1) streamwise vortices generated using vortex generators (VGs), (2) spanwise vortices generated using a novel concept of an elevated wire (EW), and (3) a cavity to act as a reservoir for the reverse flow accumulation. The methods were observed to delay the onset of DS by several degrees as well as reduce the increased lift and drag forces that are associated with the DSV. However, only the VG and the EW were observed to improve the post-stall characteristics of the airfoil.

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Section: Elevated Wirementioning

confidence: 93%

Methods to control dynamic stall for wind turbine applications

2016

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“…Numerical and experimental investigations have shown that boundary layer transition can affect the dynamic stall characteristics of rotor blade airfoils (Ref. 31). Therefore, when aiming for an improved numerical prediction of dynamic stall, boundary layer transition must not be neglected.…”

Section: Influence Of Transition Predictionmentioning

confidence: 99%

Improved Two-Dimensional Dynamic Stall Prediction with Structured and Hybrid Numerical Methods

Richter¹,

Pape²,

Knopp³

et al. 2011

j am helicopter soc

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A joint comprehensive validation activity on the structured numerical method elsA and the hybrid numerical method TAU was conducted with respect to dynamic stall applications. To improve two-dimensional prediction, the influence of several factors on the dynamic stall prediction was investigated. The validation was performed for three deep dynamic stall test cases of the rotor blade airfoil OA209 against experimental data from two-dimensional pitching airfoil experiments, covering low-speed and high-speed conditions. The requirements for spatial discretization and for temporal resolution in elsA and TAU are shown. The impact of turbulence modeling is discussed for a variety of turbulence models ranging from one-equation Spalart-Allmaras-type models to state-of-the-art, seven-equation Reynolds stress models. The influence of the prediction of laminar/turbulent boundary layer transition on the numerical dynamic stall simulation is described. Results of both numerical methods are compared to allow conclusions to be drawn with respect to an improved prediction of dynamic stall. Nomenclatureb span, m c chord, m c d , c d drag coefficient, difference in drag coefficient c l , c l lift coefficient, difference in lift coefficient c m , c m pitching moment coefficient, difference in pitching moment coefficient f frequency, Hz M Mach number r radius, m Re Reynolds number s, s LE , s max cell size, cell size at airfoil leading-edge, maximum cell size, m T period, s v ∞ freestream velocity, m/s x, y coordinates, m y + normalized wall distance α, α angle of attack, difference in angle of attack, deg t timestep, s ω * reduced frequency, ω * = 2πfc/v ∞

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“…Dynamic stall consists of a separation of the boundary layer from the suction-side surface of the blade and subsequent roll-up into a leading edge vortex, which can introduce excessive structural vibrations, reduce efficiency, and produce unwanted noise. Although dynamic stall is a dominating feature of vertical axis wind turbine flows, it has been studied extensively in many other contexts (McCroskey, 1976;Leishman and Beddoes, 1986;Carr, 1988;Geissler and Haselmeyer, 2006;Buchner et al, 2012;. On horizontal axis wind turbines, for example, even mild stall decreases performance and increases noise production significantly (Hibbs, 1986;Loratro et al, 2014), and similar effects are experienced to a greater magnitude by vertical axis turbines (Allet and Paraschivoiu, 1995;Scheurich and Brown, 2011).…”

Section: Introductionmentioning

confidence: 96%