Field-Scale Lagrangian Particle Tracking Using Soap Bubbles in Wind Turbine Wakes

Capturing the wake dynamics behind wind turbines in the field remains challenging due to the spatial and temporal scales involved. Conventional field measurement techniques such as LIDAR and sonic anemometers are not sufficient to fully resolve small scale structures such as tip vortices, which dominate the evolution of the near wake. However, Lagrangian Particle Tracking offers a promising alternative by providing time-resolved, three-dimensional velocity data. Lagrangian Particle Tracking has primarily been used in laboratory settings, its application to field scales only emerging recently due to significant practical challenges.

We present a field experiment designed to perform large-scale 3D Lagrangian particle tracking in the wake of a mid-sized wind turbine. The setup uses neutrally buoyant soap bubbles as tracers, imaged by four high-speed Phantom cameras capturing a measurement volume of about 8m x 6m x 10m at 900Hz. This allows us to resolve the evolution of tip vortices and their interaction with the surrounding flow. The long-term goal of this work is to image the largest possible field of view in order to study the flow behind wind turbines and other large-scale structures.