*WINNER* Wind farm yaw control: Why positive yaw angles can enhance the production, while negative angles lead to an overall loss of power?

Abstract

The aerodynamic interactions of wind turbines within a wind farm cause major energy losses. While these unavoidable interactions are minimized via layout optimizations prior to the construction of the wind farm, some active treatments can be carried out to further tackle this issue during the operation of the plant. Among all, yaw control has appeared to be the most promising strategy. Studying the impact of intentional yaw misalignment on the wake characteristics and the performance of wind farms has led to the conclusion that proper positive yaw misalignment can lead to an overall increase in the annual energy production of a wind farm, while any negative misalignment always reduces the energy production. Two unverified reasons are proposed for this: (i) clockwise rotation of the turbine blades and (ii) the Coriolis effect. This paper investigates these two potential explanations by conducting six large-eddy simulations of flow through a wind farm of 10 turbines. Results indicate that the Coriolis force and the direction of rotation of the blades both contribute to the significant inconsistency between the impact of positive and negative yaws on the net power production. The Coriolis force, however, was found to be more influential at the studied hub height. For the studied case, the difference between applying a positive and a negative yaw angle to the front-row turbine was found to be approximately 17%. This difference was reduced to almost 7% when the Coriolis force was relaxed, and to approximately 11% when the turbines were set to rotate counterclockwise.