Vestas—Page 2

VestasVortex generators exist in different sizes and types. Counterrotating vortex generators are the most effective and are usually used for wind turbine applications. They comprise a pair of small delta fin wings, mounted equidistantly, opposite each other on the suction (leeward) side of the blade. The delta fin wings are inclined to the incoming flow to produce a pair of counter-rotating vortices that are swept downstream to re-energise local, low-momentum flows. Blades with large inner rotor separated flow regions can benefit strongly from vortex generators. However, vortex generators are less effective in blades with lower flow separation, such as the V90 and V100 blades. In this case we also employ gurney flap devices to improve energy yield . Typically, gurney flaps, named after American race car driver Dan Gurney, are small, flat plates fitted at a right angle to the windward side of the blade along the trailing edge. The gurney flap effectively changes the camber of the aerofoil near the trailing edge, which can increase lift substantially without significant drag penalty. The efficacy of a gurney flap depends on the height of the device and span-wise position along the length of the blade. The gurney flap’s dimensions must be chosen carefully to balance the increased load and performance of the blade. For wind turbine blade applications, gurney flaps are most effective on the inner part of the blade, where a relatively thick aerofoil section benefits from the additional lift provided by the flap. The gurney flap works best when operating in attached flow, where it combines beneficially with vortex generators. Our wind tunnel test measurements further helped optimise gurney flap geometry and performance. Figure 1 Example of a counter-rotating vortex generator The shed vortices help to suppress or delay blade flow separation, which enhances the blade segment’s power output and captures power previously lost through early flow separation and stall. Vestas has developed vortex generators through extensive wind tunnel testing and field measurements, examining a wide range of wind speeds to increase the wind turbine’s power output. Systematic testing under both controlled and field environments allowed us to verify predictions in flow separation and flow separation control. In turn, this assisted our delivery of cost-effective, durable, reliable and simple-to-install devices. Vestas 3D flow simulations also helped identify the best positioning of vortex generators near to the root of different blade types – taking into account their individual flow characteristics to improve upon. Figure 2 Example of gurney flaps on a wind turbine bladePage 1Page 3