HAWT dynamic stall response asymmetries under yawed flow conditions

Schreck, S.; Robinson, Michael C.; Hand, M.; Simms, D.

doi:10.1002/we.40

Cited by 35 publications

(16 citation statements)

References 19 publications

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“…On the other hand, dynamic stall has also been observed on wind turbine blades [8e11], where it leads to increased fatigue damage accumulation at the rotor-hub joint due to large excursion in lift [12] as well as increased noise generation due to blade-vortex interaction [13]. In wind turbines, dynamic stall is caused by rapid variations of wind speed and direction [8,14,15] and is, therefore, more unpredictable compared to the rotor blades of helicopters. Furthermore, due to operation in the wake of other turbines, which consists of large-scale vortical structures of high turbulence intensity and velocity deficits [9,16e18], the problem of dynamic stall is considerably aggravated for downstream wind turbines [9].…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

Methods to control dynamic stall for wind turbine applications

2016

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“…These measurements formed a basis for further understanding 3D flow effects and dynamic stall in a rotating environment, which is crucial for improving engineering modelling tools. Schreck et al [3] analyzed the experimental surface pressures and normal force histories to characterize the dynamic stall vortex kinematics and normal force amplification for a rotating blade observed in the NREL Phase IV Unsteady Aerodynamics Experiment. Stall vortex convection was found to vary along the blade, leading to rapid deformation of the vortex and amplification of normal forces.…”

Section: Introductionmentioning

confidence: 99%

Combining Unsteady Blade Pressure Measurements and a Free-Wake Vortex Model to Investigate the Cycle-to-Cycle Variations in Wind Turbine Aerodynamic Blade Loads in Yaw

Elgammi

Sant

2016

Energies

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Prediction of the unsteady aerodynamic flow phenomenon on wind turbines is challenging and still subject to considerable uncertainty. Under yawed rotor conditions, the wind turbine blades are subjected to unsteady flow conditions as a result of the blade advancing and retreating effect and the development of a skewed vortical wake created downstream of the rotor plane. Blade surface pressure measurements conducted on the NREL Phase VI rotor in yawed conditions have shown that dynamic stall causes the wind turbine blades to experience significant cycle-to-cycle variations in aerodynamic loading. These effects were observed even though the rotor was subjected to a fixed speed and a uniform and steady wind flow. This phenomenon is not normally predicted by existing dynamic stall models integrated in wind turbine design codes. This paper couples blade pressure measurements from the NREL Phase VI rotor to a free-wake vortex model to derive the angle of attack time series at the different blade sections over multiple rotor rotations and three different yaw angles. Through the adopted approach it was possible to investigate how the rotor self-induced aerodynamic load fluctuations influence the unsteady variations in the blade angles of attack and induced velocities. The hysteresis loops for the normal and tangential load coefficients plotted against the angle of attack were plotted over multiple rotor revolutions. Although cycle-to-cycle variations in the angles of attack at the different blade radial locations and azimuth positions are found to be relatively small, the corresponding variations in the normal and tangential load coefficients may be significant. Following a statistical analysis, it was concluded that the load coefficients follow a normal distribution at the majority of blade azimuth angles and radial locations. The results of this study provide further insight on how existing engineering models for dynamic stall may be improved through the integration of stochastic models to be able to account for the cycle-to-cycle variability in the unsteady wind turbine blade loads under yawed conditions.

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“…Schreck (see [36,37]) investigated the 3D dynamic stall processes on the NREL UAE Phase VI rotor through the analysis of blade surface pressure data and the local inflow angle when operating under yawed conditions. In the EU project 'Dynamic stall and 3D effects' coordinated by FFA, it was attempted to use the IEA Annex XVIII measurement to understand dynamic stall effects.…”

Section: Unsteady Aerofoil Aerodynamicsmentioning

confidence: 99%

A Review of Wind Turbine Yaw Aerodynamics

Micallef¹,

Sant²

2016

Wind Turbines - Design, Control and Applications

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The fundamental physics of HAWT aerodynamics in yaw is reviewed with reference to some of the latest scientific research covering both measurements and numerical modelling. The purpose of this chapter is to enable a concise overview of this important subject in rotor aerodynamics. This will provide the student, researcher or industry professional a quick reference. Detailed references are included for those who need to delve deeper into the subject. The chapter is also restricted to the aerodynamics of single rotors and their wake characteristics. Far wake and wind turbine to turbine effects experienced in wind farms are excluded from this review. Finally, a future outlook is provided in order to inspire further research in yawed aerodynamics.

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HAWT dynamic stall response asymmetries under yawed flow conditions

Cited by 35 publications

References 19 publications

Methods to control dynamic stall for wind turbine applications

Methods to control dynamic stall for wind turbine applications

Combining Unsteady Blade Pressure Measurements and a Free-Wake Vortex Model to Investigate the Cycle-to-Cycle Variations in Wind Turbine Aerodynamic Blade Loads in Yaw

A Review of Wind Turbine Yaw Aerodynamics

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