Combined Effect of Rotational Augmentation and Dynamic Stall on a Horizontal Axis Wind Turbine

Abstract

Rotational augmentation and dynamic stall have been extensively investigated on horizontal axis wind turbines (HAWTs), but usually as separate topics. Although these two aerodynamic phenomena mainly determine the unsteady loads and rotor performance, the combined effect of rotational augmentation and dynamic stall is still poorly understood and is challenging to model. We perform a comprehensive comparative analysis between the two-dimensional (2D) airfoil flow and three-dimensional (3D) blade flow to provide a deep understanding of the combined effect under yawed inflow conditions. The associated 2D aerodynamic characteristics are examined by the unsteady Reynolds-averaged Navier-Stokes Simulations, and are compared with the experimental data of NREL Phase VI rotor in three aspects: aerodynamic hysteresis, flow field development, and dynamic stall regimes. We find that the combined effect can dramatically reduce the sectional lift and drag hysteresis by almost 60% and 80% from the supposed definitions of hysteresis intensity, and further delay the onset of stall compared with either of rotational augmentation and dynamic stall. The flow field development analysis indicates that the 3D separated flow is greatly suppressed in the manner of changing the massive trailing-edge separation into the moderate leading-edge separation. Furthermore, the 3D dynamic stall regime indicates a different stall type and an opposite trend of the separated zone development, compared with the 2D dynamic stall regime. These findings suggest that the modelling of 3D unsteady aerodynamics should be based on the deep understanding of 3D unsteady blade flow rather than correcting the existing 2D dynamic stall models. This work is helpful to develop analytical models for unsteady load predictions of HAWTs.

Investigations on the Unsteady Aerodynamic Characteristics of a Horizontal-Axis Wind Turbine during Dynamic Yaw Processes

“…The torque value computed using the BEM method, with or without the Beddoes stall model, is higher than the value computed by CFD since the BEM computation does not consider flow separation and flow transient phenomena. Zhu [39] extensively investigated the combined effects of rotational augmentation and dynamic stall, and found that the hysteresis loop of aerodynamic load is much larger compared to 2D simulations. In fact, for the NREL 5-MW wind turbine and a wind speed of 11.4 m/s, flow separation and 3D radial flow mainly occur on the inner board region, resulting in a lower torque and lower thrust.…”

Sensitivity Study of the Influence of Blade Sectional Stiffness Parameters on the Aeroelastic Response of Wind Turbines

“…The second term at the right end of the formula is the quantity to be determined by the modified model. Both dynamic stall and three-dimensional rotation effects lead to stall delay, which is not a linear superposition relationship but a certain coupling relationship (Guntur et al, 2016;Elgammi and Sant, 2017;Zhu et al, 2019).…”

Comparative Study of Dynamic Stall between an Aircraft Airfoil and a Wind Turbine Airfoil in an Air–Particle Flow

“…Guntur et al [27] adopted the DDES SST k-ω model, which is combined with the laminar/turbulent transition modeled (the γ-Re θ model), to present the combined effects of dynamic stall and rotational augmentation in the inboard parts of wind turbine blades. A further investigation was implemented by Zhu et al [28]; they employed the transition SST model and found that these combined effects can dramatically reduce the sectional lift, drag hysteresis by almost 60% and 80%, and delay the onset of stall, compared to either the rotational augmentation and dynamic stall. Li et al [29,30] employed the plasma flow to optimize the performance of airfoil dynamic stall in the experiment and numerical calculation, respectively.…”