Combined effect of passive vortex generators and leading-edge roughness on dynamic stall of the wind turbine airfoil

Passive vortex generators (VGs) have been widely applied on wind turbines to boost the aerodynamic performance. Although VGs can delay the onset of static stall, the effect of VGs on dynamic stall is still incompletely understood. Therefore, this paper aims at investigating the deep dynamic stall of NREL S809 airfoil controlled by single-row and double-row VGs. The URANS method with VGs fully resolved is used to simulate the unsteady airfoil flow. Firstly, both single-row and double-row VGs effectively suppress the flow separation and reduce the fluctuations in aerodynamic forces when the airfoil pitches up. The maximum lift coefficient is therefore increased beyond 40%, and the onset of deep dynamic stall is also delayed. This suggests that deep dynamic-stall behaviors can be properly controlled by VGs. Secondly, there is a great difference in aerodynamic performance between single-row and double-row VGs when the airfoil pitches down. Single-row VGs severely reduce the aerodynamic pitch damping by 64%, thereby undermining the torsional aeroelastic stability of airfoil. Double-row VGs quickly restore the decreased aerodynamic efficiency near the maximum angle of attack, and also significantly accelerate the flow reattachment. The second-row VGs can help the near-wall flow to withstand the adverse pressure gradient and then suppress the trailing-edge flow separation, particularly during the downstroke process. Generally, double-row VGs are better than single-row VGs concerning controlling deep dynamic stall. This work also gives a performance assessment of VGs in controlling the highly unsteady aerodynamic forces of a wind turbine airfoil.

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Numerical Investigation of Passive Vortex Generators on a Wind Turbine Airfoil Undergoing Pitch Oscillations

Energies ◽

10.3390/en12040654 ◽

2019 ◽

Vol 12 (4) ◽

pp. 654 ◽

Cited By ~ 5

Author(s):

Chengyong Zhu ◽

Tongguang Wang ◽

Jianghai Wu

Keyword(s):

Wind Turbine ◽

Stokes Equations ◽

Turbine Blades ◽

Operating Conditions ◽

Vortex Generators ◽

Dynamic Stall ◽

Wind Turbine Blades ◽

Unsteady Aerodynamic ◽

Wind Turbine Airfoil ◽

Airfoil Flow

Passive vortex generators (VGs) are widely used to suppress the flow separation of wind turbine blades, and hence, to improve rotor performance. VGs have been extensively investigated on stationary airfoils; however, their influence on unsteady airfoil flow remains unclear. Thus, we evaluated the unsteady aerodynamic responses of the DU-97-W300 airfoil with and without VGs undergoing pitch oscillations, which is a typical motion of the turbine unsteady operating conditions. The airfoil flow is simulated by numerically solving the unsteady Reynolds-averaged Navier-Stokes equations with fully resolved VGs. Numerical modelling is validated by good agreement between the calculated and experimental data with respect to the unsteady-uncontrolled flow under pitch oscillations, and the steady-controlled flow with VGs. The dynamic stall of the airfoil was found to be effectively suppressed by VGs. The lift hysteresis intensity is greatly decreased, i.e., by 72.7%, at moderate unsteadiness, and its sensitivity to the reduced frequency is favorably reduced. The influences of vane height and chordwise installation are investigated on the unsteady aerodynamic responses as well. In a no-stall flow regime, decreasing vane height and positioning VGs further downstream can lead to relatively high effectiveness. Compared with the baseline VG geometry, the smaller VGs can decrease the decay exponent of nondimensionalized peak vorticity by almost 0.02, and installation further downstream can increase the aerodynamic pitch damping by 0.0278. The obtained results are helpful to understand the dynamic stall control by means of conventional VGs and to develop more effective VG designs for both steady and unsteady wind turbine airfoil flow.

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Dynamic stall control of the wind turbine airfoil via single-row and double-row passive vortex generators

Energy ◽

10.1016/j.energy.2019.116272 ◽

2019 ◽

Vol 189 ◽

pp. 116272 ◽

Cited By ~ 5

Author(s):

Chengyong Zhu ◽

Jie Chen ◽

Jianghai Wu ◽

Tongguang Wang

Keyword(s):

Wind Turbine ◽

Vortex Generators ◽

Dynamic Stall ◽

Double Row ◽

Single Row ◽

Wind Turbine Airfoil ◽

Stall Control

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Flow control on wind turbine airfoil affected by the surface roughness using leading-edge protuberance

Journal of Renewable and Sustainable Energy ◽

10.1063/1.5116414 ◽

2019 ◽

Vol 11 (6) ◽

pp. 063304 ◽

Cited By ~ 3

Author(s):

Yinan Zhang ◽

Mingming Zhang ◽

Chang Cai

Keyword(s):

Surface Roughness ◽

Flow Control ◽

Wind Turbine ◽

Leading Edge ◽

Wind Turbine Airfoil

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Aerodynamic Analysis of an Airfoil With Leading Edge Pitting Erosion

Journal of Solar Energy Engineering ◽

10.1115/1.4037380 ◽

2017 ◽

Vol 139 (6) ◽

Cited By ~ 2

Author(s):

Yan Wang ◽

Ruifeng Hu ◽

Xiaojing Zheng

Keyword(s):

Wind Turbine ◽

Indirect Effects ◽

Leading Edge ◽

Aerodynamic Performance ◽

Navier Stokes ◽

Distribution Area ◽

Navier Stokes Equation ◽

Turbine Performance ◽

Wind Turbine Airfoil ◽

Cfd Method

Leading edge erosion is a considerable threat to wind turbine performance and blade maintenance, and it is very imperative to accurately predict the influence of various degrees of erosion on wind turbine performance. In the present study, an attempt to investigate the effects of leading edge erosion on the aerodynamics of wind turbine airfoil is undertaken by using computational fluid dynamics (CFD) method. A new pitting erosion model is proposed and semicircle cavities were used to represent the erosion pits in the simulation. Two-dimensional incompressible Reynolds-averaged Navier–Stokes equation and shear stress transport (SST) k–ω turbulence model are adopted to compute the aerodynamics of a S809 airfoil with leading edge pitting erosions, where the influences of pits depth, densities, distribution area, and locations are considered. The results indicate that pitting erosion has remarkably undesirable influences on the aerodynamic performance of the airfoil, and the critical pits depth, density, and distribution area degrade the airfoil aerodynamic performance mostly were obtained. In addition, the dominant parameters are determined by the correlation coefficient path analysis method, results showed that all parameters have non-negligible effects on the aerodynamics of S809 airfoil, and the Reynolds number is of the most important, followed by pits density, pits depth, and pits distribution area. Meanwhile, the direct and indirect effects of these factors are analyzed, and it is found that the indirect effects are very small and the parameters can be considered to be independent with each other.

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Aerodynamic Performance of Wind Turbine Airfoil DU 91-W2-250 under Dynamic Stall

Applied Sciences ◽

10.3390/app8071111 ◽

2018 ◽

Vol 8 (7) ◽

pp. 1111 ◽

Cited By ~ 6

Author(s):

Shuang Li ◽

Lei Zhang ◽

Ke Yang ◽

Jin Xu ◽

Xue Li

Keyword(s):

Wind Turbine ◽

Aerodynamic Performance ◽

Dynamic Stall ◽

Wind Turbine Airfoil

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Parametric exploration on the airfoil design space by numerical design of experiment methodology and multiple regression model

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650919850426 ◽

2019 ◽

Vol 234 (1) ◽

pp. 3-18 ◽

Cited By ~ 1

Author(s):

Xingxing Li ◽

Ke Yang

Keyword(s):

Regression Model ◽

Wind Turbine ◽

Multiple Regression ◽

Design Space ◽

Leading Edge ◽

Multiple Regression Model ◽

Highly Nonlinear ◽

Numerical Design ◽

Wind Turbine Airfoil ◽

The Cost

Robust airfoil design is crucial to efficient, stable, and safe operation for modern wind turbines. However, even for deterministic wind turbine airfoil design, the problem is complex regarding to aerodynamic, acoustic, and structural requirements of wind turbine blades. Therefore, this study aims to assess the design variable impact, identify significant variables, and obtain the correlation with the airfoil responses, to reduce the cost of the airfoil robust optimization. In this paper, the optimal hypercube design method was applied to an airfoil designed by the National Advisory Committee for Aeronautics, NACA 63-421, which is commonly employed in the outboard modern wind turbine blade, to perform the numerical design of experiments. Then, a parametric exploration on the characteristics of airfoil design space by the multiple regression model and statistical analysis method were conducted. It was identified that in regular design space, the variations of aerodynamic and structural parameters are dominated by the airfoil camber and radius of leading edge. Meanwhile, the chord-wise position of the maximum thickness also has strong impacts on the airfoil performance. In further, the overall design spaces are explored to be highly nonlinear in aerodynamic and acoustic responses because of the nonlinear effects of the airfoil chord-wise position of the maximum camber and radius of leading edge. Strong but undesirable correlations were demonstrated between the maximum lift-to-drag ratio and the total sound pressure level. These findings could serve as a valuable guidance for wind turbine airfoil robust design to screen the stochastic design variables, simplify the design space, and reduce the cost.

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