Visualizing turbulent flows with Particle Image Velocimetry (PIV)
How does the wind flow around the rotor blade of a wind turbine? What does this flow look like when a gust hits the blade? To answer these and other questions, ForWind scientists carry out experiments in the large Oldenburg wind tunnel. Tiny particles are added to the inflowing air and illuminated by laser light, and high-speed cameras record the movements of the particle streams. With this method, known as particle image velocimetry (PIV), the particles of an entire flow field are photographed, and the flow direction and velocity are calculated from the change in their position from one photo to the next. The cameras take up to 12,000 images per second, which gives the results a very high temporal and spatial resolution. A further advantage of the PIV method is that the optical measuring method itself does not influence the flow. Now it has been possible to use this measurement method in the large wind tunnel with turbulent flows on a rotating model wind turbine. The results show how the wind flows around the moving rotor blade (see figure and video). Of particular interest is when and how the flow detaches from the rotating blade and which wind situations lead to the largest impacts and thus to the greatest dynamic loads on the components of the wind turbine. With this knowledge, measures to reduce these loads can be improved, which extends the service life of the rotor blades and the other components of the wind turbine.
In the research project TurbuMetric, the PIV measurement method is combined with other measurement techniques in order to record the turbulent flow and the deformation of the rotor blades simultaneously.