Passive vane–type vortex generators (VGs) are commonly used on wind turbine blades to mitigate the effects of flow separation. However, significant uncertainty surrounds VG design guidelines. Understanding the influence of VG parameters on airfoil performance requires a systematic approach targeting wind energy‐specific airfoils. Thus, the 30%‐thick DU97‐W‐300 airfoil was equipped with numerous VG designs, and its performance was evaluated in the Delft University Low Turbulence Wind Tunnel at a chord‐based Reynolds number of 2×106. Oil‐flow visualizations confirmed the suppression of separation as a result of the vortex‐induced mixing. Further investigation of the oil streaks demonstrated a method to determine the vortex strength. The airfoil performance sensitivity to 41 different VG designs was explored by analysing model and wake pressures. The chordwise positioning, array configuration, and vane height were of prime importance. The sensitivity to vane length, inclination angle, vane shape, and array packing density proved secondary. The VGs were also able to delay stall with simulated airfoil surface roughness. The use of the VG mounting strip was detrimental to the airfoil's performance, highlighting the aerodynamic cost of the commonly used mounting technique. Time‐averaged pressure distributions and the lift standard deviation revealed that the presence of VGs increases load fluctuations in the stalling regime, compared with the uncontrolled case.

Two new engineering models are presented for the aerodynamic induction of a wind turbine under dynamic thrust. The models are developed using the differential form of Duhamel integrals of indicial responses of actuator disc type vortex models. The time constants of the indicial functions are obtained by the indicial responses of a linear and a nonlinear actuator disc model. The new dynamic‐inflow engineering models are verified against the results of a Computational Fluid Dynamics (CFD) model and compared against the dynamic‐inflow engineering models of Pitt‐Peters, Øye, and Energy Research Center of the Netherlands (ECN), for several load cases. Comparisons of all models show that two time constants are necessary to predict the dynamic induction. The amplitude and phase delay of the velocity distribution shows a strong radial dependency. Verifying the models against results from the CFD model shows that the model based on the linear actuator disc vortex model predicts a similar performance as the Øye model. The model based on the nonlinear actuator disc vortex model predicts the dynamic induction better than the other models concerning both phase delay and amplitude, especially at high load.

No abstract

No abstract

To advance the design of a multimegawatt vertical‐axis wind turbine (VAWT), application‐specific airfoils need to be developed. In this research, airfoils are tailored for a VAWT with variable pitch. A genetic algorithm is used to optimise the airfoil shape considering a balance between the aerodynamic and structural performance of airfoils. At rotor scale, the aerodynamic objective aims to create the required optimal loading while minimising losses. The structural objective focusses on maximising the bending stiffness. Three airfoils from the Pareto front are selected and analysed using the actuator cylinder model and a prescribed‐wake vortex code. The optimal pitch schedule is determined, and the loadings and power performance are studied for different tip‐speed ratios and solidities. The comparison of the optimised airfoils with similar airfoils from the first generation shows a significant improvement in performance, and this proves the necessity to properly select the airfoil shape.

To assess and optimize vortex generators (VGs) for flow separation control, the effect of these devices should be modelled in a cost and time efficient way. Therefore, it is of interest to extend integral boundary layer models to analyse the effect of VGs on airfoil performance. In this work, the turbulent boundary layer formulation is modified using a source term approach. An additional term is added to the shear-lag equation, to account for the increased dissipation due to streamwise vortex action in the boundary layer, forcing transition at the VG leading edge where applicable. The source term is calibrated and a semi-empirical relation is set up and implemented in XFOIL. The modified code is capable of addressing the effect of the VG height, length, inflow angle, and chordwise position on the airfoil's aerodynamic properties. The predicted polars for airfoils with VGs show a good agreement with reference data, and the code robustness is demonstrated by assessing different airfoil families at a wide range of Reynolds numbers. KEYWORDSintegral boundary layer, separation control, source term, vortex generator, Xfoil INTRODUCTIONFor the next generation of wind turbines, manufacturers aim to design multimegawatt rotors to improve the competitiveness of wind energy technology. To up-scale wind turbines, novel technologies are required and new design challenges will appear. One such aerodynamic challenge is the management of separated flow. Preventing or at least delaying separation over the blades can positively affect the annual energy production (AEP).On top of that, the magnitude and severe variations of the aerodynamic loads associated with separating flows can be reduced, mitigating structural fatigue issues. In the wind energy industry, separation control is often realized by using passive vortex generators (VGs).Vortex generators improve the resistance of a boundary layer against flow separation by re-energizing the flow close to the surface. The streamwise vortices shed from the free tips of the VGs enhance mixing between the high-energy flow in the outer part of the boundary layer with the low-energy regions near the walls (see Schubauer and Spangenberg. 1 ) The physics involved is nontrivial and poses a number of modelling challenges.To achieve a cost-effective scale up of current turbines, it will become necessary to evolve towards a multidisciplinary design process where VGs are already incorporated early in the design phase. To assess and optimize the use of VGs, there will be a need to effectively model these devices in a cost and time efficient manner. BackgroundNumerous VG modelling techniques have been explored in literature, most of which use computational fluid dynamics (CFD). The most direct and intuitive approach is to model the effect of VGs by including them as a local geometrical protrusion in the domain. This approach requires a fully . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...

In this paper, the actuator‐in‐actuator cylinder (AC‐squared) model is presented. This model is an extension of the original actuator cylinder model of Madsen and is capable of modelling the effect of a two concentric actuation surfaces in 2D. The induced velocity at every point in the 2D field is affected by the force field acting on the two actuator cylinders. The equations are derived, and a model verification is performed using analytical solutions of flows, proof of flow equivalence, and using OpenFOAM calculations. Finally, the model is applied to different case studies, and the results are compared with a time‐dependent free wake vortex method.

Since the first commercial projects, the development of vertical-axis wind turbines (VAWTs) has been impeded by the limited understanding and inability to accurately model VAWTs. This paper investigates and compares different aerodynamic modelling techniques for VAWTs in 3D. All considered models are using the same blade-element characteristics but use different descriptions to determine the induced velocity field. The H-and Φ-rotor are studied with various aspect ratios and rotor loadings. Both instantaneous azimuthal parameters as well as integral parameters, such as the thrust and power are investigated. The paper concludes that capturing the 3D effects of VAWTs is challenging and the trends to be expected are not straightforward due to the complex vortex system created by VAWTs. All model assumptions affect the results both at the mid-plane of the rotor as well as at the blade tips.