A2 - Dynamic flow separation on large reactive rotor blades of wind energy megastructures.

The increase in power output of today's wind turbines (WTs) demanded as part of the expansion of wind energy leads to an increase in the rotor diameter of future WTs, as the power output of a WT increases quadratically with its rotor diameter. The long, slender and flexible rotor blades of such megastructures will be more susceptible to vibrations than today's rotor blades. They will be excited to vibrate, for example, by cyclical pitch control, rotor-tower interaction, cyclically changing inflow conditions due to different wind speeds during a rotor revolution in the atmospheric ground boundary layer or by turbulence-induced noise. On the rotor blade itself, vibration-induced velocities or turbulence fluctuations lead to strong, transient changes in the angle of attack, which can cause the flow on the profile to enter the range of dynamic flow separation. In addition, the flow around the profile and its separation behavior at future megastructures will be influenced by turbulence intensities varying over the height, which did not have to be taken into account for plants of the previous size. In the area of dynamic flow separation, excessive transient loads occur, which excite transient, aeroelastic interactions between flow and rotor blade. This additional excitation introduces mechanical fatigue loads that, in the case of resonance, can lead to the destruction of the rotor blade. The consideration of these loads and the associated aeroelastic stability of the rotor blade is therefore a decisive factor in the design of future wind turbine megastructures.

The working hypothesis of this sub-project is that dynamic flow separation must already be taken into account during the design of rotor blades of future wind turbine megastructures in order to minimize aeroelastic interactions. Previous models are not applicable here, as these are based on empirical data that must be determined experimentally for the respective profile geometry.

With this second model, it will be possible to systematically investigate the influence of various profile design parameters on the profile loads during dynamic flow separation on wind turbine profiles. Insights will then be drawn from this to develop a reduced-order model of dynamic flow separation for use in blade element momentum (BEM) simulations. This model is then applicable in an iterative design process. An optimized airfoil geometry will be developed during the first funding period and a direct integration of the dynamic flow separation model into the digital twin is targeted for a possible second funding period. In addition, an evaluation of the aeroelastic stability of the rotor blade is taking place within the framework of this sub-project in order to be able to make any necessary adjustments to the overall system design in the digital twin.