Performance increase and improvement of the fatigue strength of vertical axis water turbines through active blade adjustment

• Applicants: Professor Dr.-Ing. Roberto Leidhold; Professor Dr. Dominique Thévenin
• Subject Area: Fluid Mechanics ; Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 457325924

Darrieus turbines are lift driven vertical axis cross flow wind and water turbines (VAWT). The turbine’s best operation range is in a tip-speed-ratio between 2 and 5 (ratio between the tangential blade to flow speed). They can become an interesting solution for electrical power generation from renewable energy sources like wind, river, ocean or tidal energy. They also offer a significant higher efficiency in the area exploitation, compared to horizontal axis based systems. Their functionality is independent of the flow direction; they can easily be conceived as a modular system, which is economically promising. However, the flow in the turbine is very complex. Until now there exists no satisfying analytical model for its aerodynamical behavior, which would allow a simple design comparable to horizontal axis turbines (HAWT). The angle of incidence, the relative speed, and thus the turbulence properties change with the rotation angle of the rotor. This leads to dynamic stall during a noticeable part of each revolution. By actively pitching the angle of attack, the efficiency can be significantly raised, as well as the self-starting capability, due to the inhibition of deep stalling. In contrast to HAWT, the pitch function is not only depending on the tip-speed-ratio, but also on the rotation angle.This requires a highly dynamical control system, with control response times depending of the revolution speed. In an interdisciplinary project, involving the fields of fluid mechanics and electrical drive systems, the following objectives will be achieved in two years, implementing three work packages with experimental focus:1. Improving the turbine’s efficiency2. Improving the fatigue resistance by minimizing the load variations3. Getting a better knowledge of the fluid mechanics in VAWT, in particular concerning dynamic stall.4. Experimental-based design of an optimization algorithm to estimate the optimized trajectory for the active pitch control5. Development of a new class of Limited-Angle Torque Motor with a thin and long format allowing the integration of the pitch actuators in the rotor blades. The decentralized mounted actuators should allow a higher degree of freedom for the improvement of the turbine efficiency.6. Design of a high dynamic trajectory control with minimal energy cost for the torque motors.

• DFG Programme: Research Grants