The objective of this task is to define and assess innovative structural concepts for achieving lightweight rotor blades with adequate stiffness and strength, but also new requirements for the implementation of smart/adaptive rotor blade concepts.For the assessment of the concepts, the new blade structural designs should pass all set criteria defined in WP1 of stiffness, stability and fatigue strength. All alternative structural concepts will be evaluated against current manufacturing capabilities and limitations, as well as projections on near future potential. Research will focus on different solutions for the structural part: use of hybrid composites (DTU), variable angle tow composites (U-Bristol), use of ribs & space frames (Fraunhofer, CRES and U-Patras), use of grid reinforcement (TUD), use of ribs / stiffeners (CRES and U-Patras), bend twist coupling for load alleviation (PoliMilano, CENER and DTU), application of structural coupling for 2-bladed wind turbines (DTU), explosive passive response of flaps to wind loading (PoliMilano), light weight structural design and light thickness skins (Gamesa and CENER), flexible structures (WMC), structural analysis for new aerodynamic concepts (Univ of Stuttgart), new smart rotor solutions (Univ of Stuttgart, Fraunhofer) structural solutions to support necessary actuator for smart blade concept (Suzlon), structural analysis tools/lighter designs (U-Patras), structural analysis simulations (CENER) A benchmark of the various tools will be performed at the initial stages of the project which support providing
targets that should be set for the proposed concepts/designs. 'Structural concept developers/modellers' will be provided with the necessary input for a comparison run, upon definition of the reference blade. Output will be compared in terms of weight, stiffness, deflection, strength & stability and fatigue strength. Three subtasks are conducted:
Subtask 2.2.1.
New design methods: The new airfoils and aerodynamic blade lay-outs depend largely on the integrity of the structural lay-out. The integration of both in a consistent design method is a prerequisite for the design of an optimized rotor. A benchmarking of existing methods will be conducted in this subtask leading to integrated aerodynamic/structural optimization tools and optimal blade designs.
Subtask 2.2.2.
New structural concepts. A series of structural concepts and designs with potentially low blade masses and favourable adaptive and aeroelastic characteristics will be developed:
- New internal blade structures resulting in higher stiffness/weight and strength/weight blade sections, compared to current blade design (box-beam with composite girders/shear webs and unstiffened composite skin), will be investigated and designed. These include: Blade sections with load carrying grid-stiffened and/or rib-stiffened skins; blades with internal space truss structures instead of a box beam; and blades with built-in bending-torsion or bending-camber coupling through tailored fibre directions or internal geometry configurations.
- Blade sections with variable geometry airfoils using morphing leading and trailing edge segments, and expandable cords will be investigated and designed. The manufacturing process will be part of the design constraints.
Subtask 2.2.3.
Scaled manufacturing and laboratory testing. Since the structural design depends on the manufacturing method, scaled blades or parts of the new designs will be manufactured and tested in the laboratory in combination with computations, with respect to both structural and structural dynamic characteristics.