Effects of a Terrestrial Wind Farm on Planetary Boundary Layer Meteorology

The impact of a terrestrial wind farm on the planetary boundary layer is explored utilizing the wind farm parameterization for the Weather Research and Forecasting- Advanced Research model (WRF-ARW v3.4.1). Emphasis is on the development and cause of a secondary circulation that exists along the boundaries of the wake extending downstream of the wind farm. This circulation may impact vertical mass flux out of the boundary layer into the free atmosphere and may also impact surface conditions in and near the wake. Values of horizontal divergence, horizontal vorticity, and vertical velocity are analyzed to determine the structure and magnitude of this secondary circulation. Additionally, the sensitivity of this secondary circulation to wind farm size, turbine density, wind speed and direction, as well as vertical wind shear in the planetary boundary layer is tested to explore the impact of the wind farm configuration and boundary layer environment on the circulation. Simulations reveal a standing wave generated as a consequence of flow deceleration within the farm. The impacts of this standing wave on the wake and secondary circulation are explored. Simulations also reveal a correlation between increasing wind speed and increasing vertical motion and divergence/convergence associated with the circulation. This examination of the impact of the secondary circulation on the mass flux into the free atmosphere and on the surface conditions and the potential role of the standing wave on the secondary circulation should lead to a better understanding of the development and structure of the downstream wake. This understanding is particularly important for the siting and configuration of future wind farms.