The location of the laminar-turbulent transition has a direct effect on the performance of an airfoil. Thermography has been a valuable tool for boundary layer visualisation for several years in both wind tunnels and other applications. The use of high-speed and high sensitivity thermal imaging systems in combination with long focal length lenses allows applying this method to megawatt (MW) range wind turbines in operation, in which the investigated rotorblade and the measurement position are several hundred meters apart. Preliminary measurements deliver qualitative information regarding the transition location along the rotorblade, and allow comparisons between different operational states and conditions. In this article first results for a thermographic boundary layer visualisation of wind turbine rotorblades in operation are presented. The measurements were performed on a 2 MW AN-Bonus wind turbine and the research wind turbine of the University of Bremen, Germany (REpower~a 3.4 M104 with 128 hub-height).
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