The Stall Flag Method

The most critical flow property of a wind turbine rotor is whether the blades are stalled. With stall flag diagnostics, this can be determined quickly, dynamically, and non-intrusively, even on full-scale wind turbines with diameters of up to 300 meters. The precise stalled area becomes clearly visible as a function of key operational parameters such as wind speed, rotor speed, and pitch angle. Once the stalling behavior is measured, it can be corrected using Corten Vortex Generators, resulting in higher energy yield.

The Stall Flag Method has been applied to approximately 30 different wind turbines. Initially developed to improve and better understand stall-controlled wind turbines, it has also been widely used for pitch-controlled turbines. In every case, it has led to an increase in energy output. In some extreme cases, yield improvements of 12% and even 20% were observed. For modern large wind turbines, a typical yield increase ranges between 1% and 3%.

CortEnergy recommends installing stall flags on the rotor blades from the outset of a new prototype of a wind turbine. This allows for immediate diagnosis of stalling behavior, enabling corrections within a few months. As a result, when the first power curve measurements are taken, the turbine operates at optimal performance right away. This can save a year of trouble shooting time.