Numerical investigation of unsteady aerodynamics of a Horizontal‐axis wind turbine under yawed flow conditions

Abstract

In the present study, unsteady flow features and the blade aerodynamic loading of the National Renewable Energy Laboratory phase VI wind turbine rotor, under yawed flow conditions, were numerically investigated by using a three‐dimensional incompressible flow solver based on unstructured overset meshes. The effect of turbulence, including laminar‐turbulent transition, was accounted for by using a correlation‐based transition turbulence model. The calculations were made for an upwind configuration at wind speeds of 7, 10 and 15 m/sec when the turbine rotor was at 30° and 60° yaw angles. The results were compared with measurements in terms of the blade surface pressure and the normal and tangential forces at selected blade radial locations. It was found that under the yawed flow conditions, the blade aerodynamic loading is significantly reduced. Also, because of the wind velocity component aligned tangent to the rotor disk plane, the periodic fluctuation of blade loading is obtained with lower magnitudes at the advancing blade side and higher magnitudes at the retreating side. This tendency is further magnified as the yaw angle becomes larger. At 7 m/sec wind speed, the sectional angle of attack is relatively small, and the flow remains mostly attached to the blade surface. At 10 m/sec wind speed, leading‐edge flow separation and strong radial flow are observed at the inboard portion of the retreating blade. As the wind speed is further increased, the flow separation and the radial flow become more pronounced. It was demonstrated that these highly unsteady three‐dimensional aerodynamic features are well‐captured by the present method. Copyright © 2012 John Wiley & Sons, Ltd.

Harmonic balance Navier‐Stokes aerodynamic analysis of horizontal axis wind turbines in yawed wind

“…Tsalicoglou et al conducted yawed flow CFD analyses of the MEXICO wind turbine and reported a good agreement between their NS CFD and experimental data. Yu et al studied the yawed rotor flow of the NREL Phase VI turbine using overset grid NS CFD simulations and a zonal laminar‐to‐turbulent transition model. They highlighted that blade loading is significantly reduced in yawed conditions and obtained an overall good agreement of computed and measured data for all considered wind speeds and yaw angles.…”

A new stall delay algorithm for predicting the aerodynamics loads on wind turbine blades for axial and yawed conditions

“…(4))], the proposed modified tip speed ratio [equation (13)] and the proposed condition [equation (11)], respectively, while Figure 6(g)-(i) illustrates the corresponding measured normal force coefficients derived by the iterative approach (Section 3) with the same threshold radii given in Figure 6 When the yaw angle increases, the flow separation factor becomes more pronounced at the inboard area of the rotor disc of the retreating blade as shown in Figure 6(a)-(c) and in the work of Yu et al 28 Since the periodic changes in the local angle of attack, because of the aligned wind speed components to the rotor disc, are evident, the advancing blade experiences lower angle of attack distributions than those at the retreating blade. Yu et al 28 stated that the flow field at the advancing side of the blade of the NREL wind phase VI rotor at 15 m s À1 and two yaw angles of 30°and 60°is attached to the blade surface up to approximately the mid-chord followed by a separation without downstream reattachment, while the retreating blade experiences stall up to the blade tip (fully separation from the leading edge) with a radial flow dominated over the blade span. The predictions shown in Figure 6 relatively match those observed in the work of Yu et al 28 It should also be noted that the retreating side of the rotor is impacted by the root vortices mainly New stall delay model for axial and yawed flow conditions at around (30°< Ψ < 150°) as shown in Figure 6.…”

“…Yu et al 28 stated that the flow field at the advancing side of the blade of the NREL wind phase VI rotor at 15 m s À1 and two yaw angles of 30°and 60°is attached to the blade surface up to approximately the mid-chord followed by a separation without downstream reattachment, while the retreating blade experiences stall up to the blade tip (fully separation from the leading edge) with a radial flow dominated over the blade span. The predictions shown in Figure 6 relatively match those observed in the work of Yu et al 28 It should also be noted that the retreating side of the rotor is impacted by the root vortices mainly New stall delay model for axial and yawed flow conditions at around (30°< Ψ < 150°) as shown in Figure 6. This is because the shedding tip vortices at Ψ = 270°are close to the blade, affecting the radial velocity components, while they move away from the rotor plane at the 90°azimuth blade position.…”

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

“…Figure 4a,b show grids in the three different zones of the turbine (far-field, yaw cylinder, and rotation) generated using the ICEM software. The NREL 5-MW rotor was modeled including the hub (without the tower) [31]. The grid number for the far-field was 3.35 million, which is enough to transition from the inflow condition to the internal zone.…”