Experimental validation of cross-sectional modelling for Bend-Twist Coupled wind turbine blades

When assessing the future competitiveness of wind energy, both on- and off-shore, scaling up current rotor technology has been identified as one of the main challenges faced by industry. Up until this point, the cost of wind energy has continued to decrease as wind turbines increased in size. Larger rotors provide access to higher wind speeds at higher altitudes and greater total energy capture from the increased area swept by the blades. Increased blade lengths and higher wind speeds, however, also result in significantly increased loads, on the blades themselves and, subsequently, all other components of the turbine. Specifically, gust loads and cyclical fatigue loads are of concern as they directly threaten the potential lifetime of a turbine and hence its profitability.
To reduce the impact of increased loads and allow further upscaling of turbines, load alleviation techniques have seen significant interest in both academia and industry. Various authors have put forward both active and passive solutions that allow a reduction in the load sustained by the blades. One contestant in the passive category is the implementation of Bend-Twist Coupling (BTC). The introduction of BTC can be achieved by sweeping the blade, by using the anisotropic material properties of composites through unbalanced lay-ups, or through a combination of the two. It has been observed that, when BTC is used to induce twist towards feather under flap-wise bending, the maximum gust and fatigue bending loads are drastically reduced. This, in turn, reduces wear of the blades as well as other components of the turbine, as shown in literature.
While these advantages of BTC have been heavily studied in various design and optimization studies found in the literature, the underlying modelling approaches are still mostly unvalidated. Thus far, researchers have used a variety of modelling methods and analysis tools to asses the behaviour of BTC sections, beams, and blades. Comparative studies have shown frequent disagreement regarding the elastic properties and coupling behaviour especially of more realistic blade cross-sections. The uncertainty in actual BTC behaviour is critical due to the high sensitivity of aerodynamic loads to twist. Without consensus on the actual performance of coupled blade designs, specifically the amount of coupling achieved by these designs, claiming advantages and improvements remains a speculative exercise. As such, validation of the modelling tools and assumptions is required, especially for those typically used in the early stages of blade design, where different solutions will compete against one another and major investment decisions are made.
In the current work, validation and cross-verification of cross-sectional modellers BECAS and VABS alongside 3D finite element models using shell and solid elements in ABAQUS is carried out. To this end, a series of prismatic BTC beams of different cross-sections are manufactured and experimentally tested for their elastic behaviour under cantilever conditions. The performance of the manufactured beams is then compared against the predictions of the chosen modelling approaches to assess their ability to accurately capture the coupled behaviour.