Abstract
Abstract. Numerical simulations of the Vestas multi-rotor demonstrator (4R-V29) are compared with field measurements of power performance and remote sensing measurements of the wake deficit from a short-range WindScanner lidar system. The simulations predict a gain of 0 %–2 % in power due to the rotor interaction at below rated wind speeds. The power curve measurements also show that the rotor interaction increases the power performance below the rated wind speed by 1.8 %, which can result in a 1.5 % increase in the annual energy production. The wake measurements and numerical simulations show four distinct wake deficits in the near wake, which merge into a single-wake structure further downstream. Numerical simulations also show that the wake recovery distance of a simplified 4R-V29 wind turbine is 1.03–1.44 Deq shorter than for an equivalent single-rotor wind turbine with a rotor diameter Deq. In addition, the numerical simulations show that the added wake turbulence of the simplified 4R-V29 wind turbine is lower in the far wake compared with the equivalent single-rotor wind turbine. The faster wake recovery and lower far-wake turbulence of such a multi-rotor wind turbine has the potential to reduce the wind turbine spacing within a wind farm while providing the same production output.
Highlights
Over the past few decades, the rated power of wind turbines has been increased by upscaling the traditional concept of a horizontal axis wind turbine with a single three-bladed rotor
The power curve measurements show that the rotor interaction increases the power performance below the rated wind speed by 1.8 %, which can result in a 1.5 % increase in the annual energy production
A comparison of the V29 rotor models from EllipSys3D Reynolds-averaged Navier–Stokes (RANS)-actuator discs (AD) and FLEX5 is made with a HAWC2 model of the V29 provided by Vestas Wind System A/S
Summary
Over the past few decades, the rated power of wind turbines has been increased by upscaling the traditional concept of a horizontal axis wind turbine with a single three-bladed rotor. An alternative way to increase the power output of a wind turbine is the multi-rotor concept, where a single wind turbine is equipped with multiple rotors. From a cost point of view, it can be cheaper to produce a multi-megawatt wind turbine with several rotors consisting of relatively small blades that are already mass produced compared with a single-rotor wind turbine with newly designed large blades (Jamieson et al, 2014). Multi-rotor wind turbines have disadvantages; for example, a more complex tower is required and the number of components is higher compared with single-rotor wind turbines
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