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Atmospheric boundary layer impacts on wind farms

Atmospheric boundary layer impacts on wind farms
Jonathan Stephen Pennells

2018

School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UNITED KINGDOM.

ABSTRACT

Increasing demand for renewable energy sources has meant that wind power is becoming a more crucial source of energy, leading to larger wind farms. It is currently unknown whether wind farms impact the boundary layer. This thesis aims to improve our understanding of the impact from wind farms. To do this, numerical simulations are carried out in BLASIUS and WRF with an existing Wind Farm Parametrisation (WFP) being implemented in BLASIUS. Neutral boundary layer simulations are carried out in BLASIUS, with different velocities, height and capping inversion strengths. It is found that decreases in boundary layer height increase the impact from the wind farm, where the height is between 715 m and 992 m for turbines with a hub height of 95 m. Increases in velocity increase the vertical advection of horizontal momentum upstream of the turbines and greater deceleration of momentum in the wind farm. Non-dimensional analysis found jumps in the inversion layer above the wind farm for Fr < 1, and increases in the pressure perturbations for low Z flows. Comparisons are made between BLASIUS and a linear model for wind farms in neutral boundary layers. The drag term in the linear model is overestimated and should be modified to account for the logarithmic velocity profile near the surface. The assumptions made in the linear model do not inhibit its representation of the velocity and pressure perturbations within the boundary layer. The impact of a wind farm on a sea breeze is investigated using WRF simulations. It is found that a wind farm at the coast does not impact the propagation of the sea breeze but does impact the land breeze. This is due to the turbulent boundary layer which the wake is in, causing a fast decay of the wake. The land breeze propagates through the wind farms and is directly impacted.