Abstract
Flow separation is the source of several problems in a wind turbine including load fluctuations, lift losses, and vibrations. Vortex generators (VGs) are passive flow control devices used to delay flow separation, but their implementation may produce overload drag at the blade section where they are placed. In the current work, a computational model of different geometries of vortex generators placed on a flat plate has been carried out throughout fully meshed computational simulations using Reynolds Averaged Navier-Stokes (RANS) equations performed at a Reynolds number of R e θ = 2600 based on local boundary layer (BL) momentum thickness θ = 2.4 mm. A flow characterization of the wake behind the vortex generator has been done with the aim of evaluating the performance of three vortex generator geometries, namely Rectangular VG, Triangular VG, and Symmetrical VG NACA0012. The location of the primary vortex has been evaluated by the vertical and lateral trajectories and it has been found that for all analyzed VG geometries the primary vortex is developed below the boundary layer thickness δ = 20 mm for a similar vorticity level ( w x m a x ). Two innovative parameters have been developed in the present work for evaluating the vortex size and the vortex strength: Half-Life Surface S 05 and Mean Positive Circulation Γ 05 + . As a result, an assessment of the VG performance has been carried out by all analyzed parameters and the symmetrical vortex generator NACA0012 has provided good efficiency in energy transfer compared with the Rectangular VG.
Highlights
Flow control devices are gaining ground in the wind energy field since they are used for solving existing problems of operational damage to wind turbines and challenging upcoming designs
The experiment on a 2.5 MW wind turbine made by Sullivan [7] for testing the effects of Vortex generators (VGs) on the power conversion performance presented an increase of 11% in the annual energy production (AEP)
The boundary layer is modified by the vortex generator vane, so it must be well modelled in numerical simulations
Summary
Flow control devices are gaining ground in the wind energy field since they are used for solving existing problems of operational damage to wind turbines and challenging upcoming designs. Vortex generators (VGs) are passive flow control devices usually placed in pairs with an array configuration on the blade surface of interest, with the aim of modifying the airfoil pressure distribution and delaying the flow separation on it. The aspect ratio (AR) defined by the relationship between the height and device length (H/L) was kept constant It was concluded throughout CFD computations on a negligible adverse pressure gradient flat plate that the lower the device height is, the lower vortex strength level is reached, but the lower the drag penalty appears. The importance of the angle marked by a Rectangular VG and the flow direction was studied by Urkiola [14] using Reynolds Averaged Navier-Stokes (RANS)-based computations with a negligible adverse pressure gradient flat plate.
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