T 2.1 - Aerodynamic concepts for high speed, low solidity offshore rotors

This task explores and analyses aerodynamic rotor designs that until now were not possible because of size limitation, the presence of typically onshore design limitations and the lack of detailed aerodynamic knowledge which has substantially increased. The absence of noise requirements either allows a high rotational speed resulting in a low solidity rotor or favors the development towards two-bladed rotors. This will be further combined with variable chord- and tip shape concepts, multi-element airfoils and new and non-conventional airfoil shapes designed for this purpose. Furthermore downwind flexible rotors, bi-plane rotors and combinations of stall- and pitch control will be explored. The task is divided in the following three subtasks:

Subtask 2.1.1.

New aerodynamic blade designs. The tip speed will be higher than for existing turbines, allowing very slender blades, or changing of the optimum to two-bladed rotors. New blade lay-outs (e.g. curved blades) will be investigated. Targets for airfoil performance will be set.

Subtask 2.1.2.

New aerofoil design. The high tip speed will lead to high local velocities along the blade surface, so that compressibility effects need to be accounted for in the airfoil- and blade design process. A new tip airfoil section will be designed. Furthermore, multi-element and flat-back airfoils will be developed and applied as well for the blade designs of 2.1.1.

Subtask 2.1.3.

Validation by experiments. The aerodynamic performance of high tip speed rotors and new airfoils will be tested in wind tunnel in a scaled rotor experiment under realistic turbulent, intermittent inflow conditions, and as 2D wind tunnel measurements as well as in full scale rotating conditions. A new MEXICO experiment for high Reynolds number and high tip speed flow will be conducted at the DNW high speed wind tunnel facility.

21 JANUARY 2019