Lagrangian particle tracking in a high Reynolds number wind turbine wake

Wind turbines operate at high diameter-based Reynolds numbers which leads to wakes dominated by highly turbulent flows. As these turbulent wakes have a direct impact on the performances of the downstream wind turbines, understanding their evolution process is important. The wakes of wind turbines are characterized by the presence of coherent structures like tip vortices that affect mixing phenomena at the wake-freestream interface. Studying the wake dynamic from a Lagrangian perspective gives insight into the transport characteristics and mixing characteristics directly related to the wake recovery. 

Here, we present Lagrangian Particle Tracking (LPT) [1,2] measurements of a wind turbine wake. LPT allows for volumetric measurements of highly turbulent flows by following tracer particles within a predefined volume over an extended period of time. The LPT setup has been developed in the Variable Density Turbulence Tunnel (VDTT) [3] at the Max Planck Institute for Dynamics and Self-Organization. This wind tunnel uses pressurized SF6 to achieve full-scale Reynolds numbers on a small-scale turbine. To obtain turbulent inflow conditions, the velocity fluctuations are modified using an active grid. Illumination is provided by a 300W laser, while high temporal resolution is achieved using four Phantom high-speed cameras. As such, the experimental setup presented here allows spatial and temporal investigation of wind turbine wakes in real-world flow conditions.