Application of rod vortex generators for flow separation reduction on wind turbine rotor

Abstract

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 ...

Review of Flow-Control Devices for Wind-Turbine Performance Enhancement

“…A novel rod vortex generator (RVG) was proposed by Suarez et al, 2016 [183] for separation control. A feasibility analysis performed on S809 aerofoil exhibited 11% increment in glide ratio and separation suppression till the AOA of 12.2 • , and these RVGs were further installed on an NREL phase-VI rotor exhibiting 0.54 and 0.67% increments in torque and thrust values, respectively [184]. Meanwhile, aerodynamic-VGs based on CLARK-Y aerofoil (11.7% thickness) [185] demonstrated an increment of nearly 4% in the glide ratio (max) with the potential for up to 25% enhancement in the performance with variations in the flow incident angle (β).…”

Variable Size Twin-Rotor Wind Turbine

“…In the case of large output wind turbines HAWT the possibility of wind turbine improvement is much smaller. It is mostly small modifications involving the flow control that are developed and investigated [10][11][12][13][14].…”

A New Flow Control and Efficiency Enhancement Method for Horizontal Axis Wind Turbines Based on Segmented Prepositive Elliptical Wings

“…In contrast, it is easier to realize the passive methods to change the characteristics of the main flow by adding auxiliary components on the external surface and mixing the airflow of the components with the main flow. For example, tip winglets [7][8][9][10], bionic leading edges [11][12][13], Gurney flaps [14][15][16], vortex generators [17][18][19][20][21][22][23][24], and other components have been added to the blades to improve the wind turbine's aerodynamic performance. Nobari et al [7] studied a wind turbine equipped with flat winglets by the finite volume method, and the wind turbine power increased by 16% after optimization.…”