DESC0023785

Wind turbine blade lengths continue to increase, up over 150% in length from 1999 to 2021, with the largest rotors on the market today exceeding lengths of over 110 meters. In addition, the expansion of onshore and offshore wind projects into lower wind speed sites require the development of low specific power products with ever increasing blade length. The net result of the rotor growth leads directly to increased variability in blade loading, which in turn increases the weight and cost of the blade and turbine components. In addition, many low wind speed sites are also subject to extreme wind conditions associated with hurricanes and tropical storms. This increase in blade loading variability necessitates the need for the development of novel advanced load control techniques. Current approaches used to address this problem have focused on a variety of active aerodynamic features that can manipulate the blade airfoil cross section to reduce the loading generated by the blade. The challenges associated with prior approaches either consist of complex actuation mechanisms that are ill-suited to the operational environment of modern wind blades or require the integration of sensing and control mechanisms to sense, activate and deploy the aerodynamic feature. To overcome these challenges, a passive loadshedding airfoil construction will be designed in Phase I by refining the development of a novel internal web structure such that the aft 10 to 20% of the airfoil deflect sufficiently to reduce the peak airfoil lift coefficient by 25% under gust loading. During the Phase I program the concept will be reduced to a working conceptual and demonstration model. An aerodynamic model will be constructed for the 30% thick airfoil on a 15 mega-watt reference turbine, providing both aerodynamic loading for the structural model development and assessment as well as the required input to assess the blade level impact during peak loading events. Semi-empirical models for the deformation of the trailing edge assembly will be constructed and tested. The response of key architectural features will be validated, including the construction of a sub-article test. The project will seek to demonstrate the deformation of the structure subject to the expected load and return to the nominal power producing configuration after removal of the load. The impact of the passive loadshedding trailing edge to enable the design of a longer blade will be demonstrated analytically. By taking advantage passive loadshedding technology, manufacturers can increase blade length by 7 to 10%, allowing the turbine to produce up to 4% additional annual energy production with the existing platform.