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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 [...]