In situ and remotely-sensed mean and turbulence characteristics of wind turbine wakes

With increasing deployment of wind turbines around the world, understanding how turbines extract energy from the wind is critical for estimating any limits to wind energy production and in understanding downstream impacts. High-resolution measurements of wind speed, temperature, and turbulence across the entire turbine rotor disk are essential to evaluate the effects of shear, stratification, and turbulence on turbine power performance. Energy dissipation rate measurements are also required for insight into wake dissipation processes. These data are lacking from current measurement practices, thereby limiting our understanding of atmosphere-turbine interactions and wake dynamics.

The CIRES Tethered Lifting System (TLS) is a unique state-of-the-art tethersonde, proven in numerous boundary-layer field experiments to be able to measure turbulence kinetic energy dissipation rates. In Fall 2012, two TLS will be deployed at NREL's National Wind Technology Center to collect simultaneous measurements of the inflow and outflow characteristics around the DOE 1.5 MW turbine. These measurements will enable us to study the effects of shear, stratification, and turbulence on turbine power production and wake dynamics, and compare our results with other measurement systems and wake models. In addition to these in situ measurements, the experimental design requires accurate and timely information on the location of the turbine wake, which will be provided by a Leosphere 200S scanning lidar deployed nearby. This presentation will highlight some of the observations from this field campaign on wake wind speed deficits (observed with both in situ and remotely sensed instrumentation), turbulence enhancement (observed with the remote sensing instruments), and turbulent kinetic energy dissipation rate (observed with the in situ instruments).