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This paper focuses on flow control on wind turbine blades. A rod vortex generator (RVG) is proposed. Previous experimental and numerical results obtained for channels and blade sections proved RVGs to effectively enhance the streamwise shear stresses and reduce flow separation. The benefits of application of RVGs to control and decrease the flow separation on horizontal axis wind turbine rotor blades are assessed and presented in the paper. The numerical investigation was conducted with the FINE/Turbo solver from Numeca International, which solves the 3D Reynoldsaveraged Navier-Stokes equations. The validation of the numerical model for the clean case is based on phase VI of the Unsteady Aerodynamics Experiment. At selected operating conditions, flow control devices have proven to reattach the flow locally to the wall and improve the aerodynamic performance of the wind turbine. Additionally, the local implementation of RVGs shows strong effect on flow structure and interaction with the main flow to create a "shielding" effect, preventing further penetration of separation towards blade tip. As a consequence, the positive effect of RVGs exists outside the blade span covered by devices. The obtained aerodynamic improvement shows that RVGs may be used as an alternative to traditional flow control devices applied on wind energy turbines. KEYWORDS flow control, flow separation, NREL phase VI, vortex generator, wind energy 1 | INTRODUCTIONSince the industrial revolution, the world demand for energy has grown at a much faster rate than in all previous human history. As a consequence, man's dependency on fossil fuels and green house gasses emissions has risen ever since. In this context, wind energy is seen as one of the most promising solutions to man's ever-increasing demands of a clean source of energy. 1 The main drawback of wind energy compared with nonrenewable energy sources is the cost of energy (COE). The COE may be reduced by increasing the annual energy production (AEP) or decreasing the operation and maintenance cost. This increase of AEP may be achieved through higher availability of the system, thereby reducing the downtime.Nevertheless, the average availability of the onshore horizontal axis wind turbines ranges from 96% to 99%, which indicates slight scope for improvement. 2 The AEP may be also enhanced by increasing wind turbine and rotor sizes. A larger turbine can capture more energy through its lifetime, decreasing the relative COE per megawatt. The last decades development in the material science, control, and aerodynamics have allowed this growth of wind turbines sizes and a continuous reduction in COE. 3 At the end of 1989, a 300-kW wind turbine with 30-m rotor diameter was state of the art; nowadays, turbines with rotor diameters of up to 160 m (Vestas V164-8MW or V164-9.5MW) have been developed, and the current trend of increasing sizes is expected to continue in the future. 4,5 Presence of flow separation on wind turbine blades leads to increased aerodynamic losses, noise generation, and fatigue ...

Purpose The purpose of this paper is to describe numerical investigations focused on the reduction of separation and the aerodynamic enhancement of wind turbine blades by a rod vortex generator (RVG). Design/methodology/approach A flow modelling approach through the use of a Reynolds-averaged Navier–Stokes solver is used. The numerical tools are validated with experimental data for the NREL Phase VI rotor and the S809 aerofoil. The effect of rod vortex generator’s (RVG) configuration on aerofoil aerodynamic performance, flow structure and separation is analysed. RVGs’ chordwise locations and spanwise distance are considered, and the optimum configuration of the RVG is applied to the wind turbine rotor. Findings Results show that streamwise vortices created by RVGs lead to modification of flow structure in boundary layer. As a result, the implementation of RVGs on aerofoil has proven to decrease the flow separation and enhance the aerodynamic performance of aerofoils. The effect on flow structure and aerodynamic performance has shown to be dependent on dimensions, chordwise location and spanwise distribution of rods. The implementation of devices with the optimum configuration has shown to increase aerodynamic performance and to significantly reduce separation for selected conditions. Application of rods to the wind turbine rotor has proven to avoid the spanwise penetration of flow separation where applied, leading to reduction of flow separation and to aerodynamic enhancement. Originality/value The proposed RVGs have shown potential to enhance the aerodynamic performance of wind turbine rotors and profiles, making devices an alternative solution to the classical vortex generators for wind turbine applications.

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