Atmospheric turbulence modelling, synthesis, and simulation

Abstract

The starting point of wind turbine operation is the incoming wind. Wind turbines are positioned in the atmospheric boundary layer (ABL), the lower approximately 1 km of the atmosphere; here the wind tends to be dominated by turbulent structures generated through the transfer of momentum and heat with the Earth's surface, as well as interaction with the free atmosphere above governed by large-scale motion. In this chapter, we will look at the turbulence affecting wind turbines from a turbulence -simulation point of view. This means that the focus will be on the properties of atmospheric turbulence which directly affect the performance and operation of wind turbines. In the ABL, turbulence is produced by mean wind shear and enhanced or destructed by buoyancy effects. This results in profiles of the various turbulence quantities across wind turbine rotors. Examples include the mean wind speed itself; second order moments, like variances and stresses; and turning of the mean wind speed and even length scales of turbulence. The degree to which a wind turbine will be affected by the turbulence in the ABL depends on its size such as rotor diameter and hub height, its power generating properties such as thrust coefficient, as well as on the applied controller which ultimately decides the operation window of the turbine. Simulations of atmospheric turbulence can guide us in quantifying the effects.