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Within the framework of the fourth phase of the International Energy Agency (IEA) Wind Task 29, a large comparison exercise between measurements and aeroelastic simulations has been carried out featuring three simulation cases in axial, sheared and yawed inflow conditions. Results were obtained from more than 19 simulation tools originating from 12 institutes, ranging in fidelity from blade element momentum (BEM) to computational fluid dynamics (CFDs) and compared to state-of-the-art field measurements from the 2 MW DanAero turbine. More than 15 different variable types ranging from lifting-line variables to blade surface pressures, loads and velocities have been compared for the different conditions, resulting in over 250 comparison plots. The result is a unique insight into the current status and accuracy of rotor aerodynamic modeling. For axial flow conditions, a good agreement was found between the various code types, where a dedicated grid sensitivity study was necessary for the CFD simulations. However, compared to wind tunnel experiments on rotors featuring controlled conditions, it remains a challenge to achieve good agreement of absolute levels between simulations and measurements in the field. For sheared inflow conditions, uncertainties due to rotational and unsteady effects on airfoil data result in the CFD predictions standing out above the codes that need input of sectional airfoil data. However, it was demonstrated that using CFD-synthesized airfoil data is an effective means to bypass this shortcoming. For yawed flow conditions, it was observed that modeling of the skewed wake effect is still problematic for BEM codes where CFD and free vortex wake codes inherently model the underlying physics correctly. The next step is a comparison in turbulent inflow conditions, which is featured in IEA Wind Task 47. Doing this analysis in cooperation under the auspices of the IEA Wind Technology Collaboration Program (TCP) has led to many mutual benefits for the

The development of renewable energy is an inevitable response to the dual challenges of the energy crisis and global warming. In many countries, wind energy has become the most cost effective renewable energy relative to other energy sources. In order to reduce the cost of electricity, modern wind turbines are increasing in rotor size and unit power. The big wind turbines currently in the market are reaching 15 MW rated power and will be possibly increased to 20 MW in a few years. In such a scenario, the continued development in wind energy has led to large rotors that are much lighter and cheaper per kilowatt than before. The main innovations include higher tip speed, higher lift and thicker airfoils, resulting in more slender and lighter blades. In the meanwhile, the coupled effects of aeroelastic and aeroacoustic behaviour and modelling have become the key research challenges. Therefore, research in many aspects of wind energy innovation is important, such that the overall objectives of low cost of energy, high system reliability and environmental-friendliness can be achieved. Several rotor design concepts have emerged to satisfy the up-scale trend, but a crucial problem is managing the large inertial loads and aeroelastic response while retaining high aerodynamic efficiency. Further utilizations of wind energy research meet the critical challenge to continuously grow in size and continuously decrease in price per kilowatt.

To alleviate global warming and reduce air pollution, the world needs to rapidly shift towards renewable energy [...]

The size of wind turbine rotors is still rapidly increasing, though many technical challenges emerge. Novel rotor designs emerge to satisfy this up-scale trend, such as downwind load-aligned concepts, which orients the loads along the blade spanwise to greatly decrease the bending moments at the root. As the studies on the aerodynamics of these rotor concepts using 3D body-fitted mesh are very limited, this paper establishes different cone configurations based on the DTU 10 MW reference rotor and conducts a series of simulations. It is found that the cone angle and the distance from the blade section to the tip vortex are two deterministic factors on conning. Upwind rotors have larger power output, less thrust, smaller wake deficit, and smaller influencing area than downwind rotors of the same size, which provides superior aerodynamic priority and benefits wind farm design. The largest upwind cone angle of 14.03 degrees, among the cases studied, leads to the highest torque to thrust ratio which is 3.63% higher than the baseline rotor. The downwind load-aligned rotor, designed to reduce the blade root bending moments at large wind speed, performs worse at the present simulation conditions than an upwind rotor of the same size.

Noise generated from wind turbines is a big challenge for the wind energy industry to develop further onshore wind energy. The traditional way of reducing noise is to design low noise wind turbine airfoils and blades. A wind turbine operating under wind shear and in yaw produces periodic changes of blade loading, which intensifies the amplitude modulation (AM) of the generated noise, and thus can give more annoyance to the people living nearby. In this paper, the noise emission from a wind turbine under wind shear and yaw is modelled with an advanced fluid-structure-acoustics framework, and then controlled with a pitch control strategy. The numerical tool used in this study is the coupled Navier–Stokes/Actuator Line model ElliSys3D/AL, structure model FLEX5, and noise prediction model (Brooks, Pope and Marcolini: BPM) framework. All simulations and tests were made on the NM80 wind turbine equipped with three blades made by LM Wind Power. The coupled code was first validated against field load measurements under wind shear and yaw, and a fairly good agreement was obtained. The coupled code was then used to study the noise source control of the turbine under wind shear and yaw. Results show that in the case of a moderate wind shear with a shear exponent of 0.3, the pitch control strategy can reduce the mean noise emission about 0.4 dB and reduce slightly the modulation depth that mainly occurs in the low-frequency region.