A Lagrangian Tracer System Using Balloons to Study Wind Farm – Atmospheric Boundary Layer Interactions

Understanding wind farm interactions with the atmospheric boundary layer (ABL) is essential for predicting wind farm performance and optimizing layout. Key processes such as wake formation, farm-to-farm interactions, and vertical momentum entrainment are strongly influenced by atmospheric stability, which affects turbulence, mixing, and thus wake recovery. Numerical and laboratory-based experimental approaches often struggle to replicate these processes due to the high Reynolds numbers and limited domain sizes, making field experiments crucial.

We present a novel Lagrangian tracer system using helium-filled biodegradable balloons equipped with lightweight radiosondes that record 3D trajectories and meteorological data. With lifetimes of up to 1.5 hours and ranges over 40 km, this system enables observations of large-scale transport and dispersion mechanisms. Balloons can be deployed via a drone to study (1) turbine wake evolution, (2) inter-farm wake interactions, and (3) vertical entrainment from the ABL. We demonstrate a proof-of-concept through deployment at a test site in Germany. Preliminary data shows how the system captures flow structures and provides insight into how dispersion, mixing, and wake behaviour vary with atmospheric stability. In parallel, we will perform synthetic balloon releases using the diurnal wind turbine dataset from the Johns Hopkins turbulence database to simulate particle trajectories and complement field observations under controlled atmospheric conditions.