» Back to overview
Proposing Institution

Institut für Aerodynamik und Gasdynamik, Uni Stuttgart
Project Manager

Dr. Thorsten Lutz
Pfaffenwaldring 21
70569 Stuttgart
The limited quantity of fossil fuels calls for new alternative energy sources. For sustainable energy economics innovative and highly efficient systems which provide clean and renewable energy are required. Only in this way, conventional power plants can be replaced. The energy share provided by wind turbines is increasing and promises to reach one of the highest percentages compared to other renewable energy sources. In order to support this development the amount of converted energy per site has to be increased so that each turbine gets as profitable as possible. Also the overall number of erected turbines is kept to a minimum and disturbance of residents in the neighbourhood is reduced. This can be achieved on the one hand by increasing turbine efficiency and on the other hand by larger rotor diameters. As turbines are growing bigger, structural issues become severe and the design reliable blades with limited weight and costs is challenging. Load reduction becomes more important because of increasing inertial and dynamic forces which are generated by atmospheric gusts and especially the tower dam. One perspective to reduce such loads is to equip the blades with controllable flaps balancing out load variations caused by inhomogeneous inflow. In case of the tower dam this is perfectly feasible because of its periodic occurrence. That could lead to more efficient structural approaches by decreasing the turbine's dynamic loads especially regarding fatigue mechanisms.Another effect of growing diameters is the coincidental growth of the Reynolds number due to higher circumferential speeds at the tip and also growing chord lengths. In addition the tip Mach number is increased. These factors affect the figure of merit in different ways as follows. Up-to-date wind turbine blades are equipped with low drag laminar airfoils which lead to delayed boundary layer transition and thereby to enhanced lift-to-drag ratios because of lower friction losses and lower friction induced pressure drag. However, counteracting this, high Reynolds numbers (in wind turbine terms 3 to 15 million) increase the amplification of disturbances in the boundary layer resulting in earlier laminar to turbulent transition.To understand these upcoming effects in detail also in combination with atmospheric inflow conditions which are relevant in the end is mandatory for providing sustainable applications of wind turbines in future. In the framework of the projects AVATAR and AssiSt the necessary investigation are being conducted. Because of the complex geometry and the necessary fine discretisation of blade and ground boundary layers CFD simulation are getting more ambitious while being more flexible and cheaper than wind tunnel tests if they are even possible. Therefor those calculations have to be conducted on high-performance computers which are capable to handle large computational setups.

Impressum, Conny Wendler