  Wind farm control using dynamic concepts is a research topic that is
receiving an increasing amount of interest. The main concept of this approach
is that dynamic variations of the wind turbine control settings lead to higher
wake turbulence, and subsequently faster wake recovery due to increased mixing.
As a result, downstream turbines experience higher wind speeds, thus increasing
their energy capture. The current state of the art in dynamic wind farm control
is to vary the magnitude of the thrust force of an upstream turbine. Although
very effective, this approach also leads to increased power and thrust
variations, negatively impacting energy quality and fatigue loading. In this
paper, a novel approach for the dynamic control of wind turbines in a wind farm
is proposed: using individual pitch control, the fixed-frame tilt and yaw
moments on the turbine are varied, thus dynamically manipulating the wake. This
strategy is named the helix approach since the resulting wake has a helical
shape. Large eddy simulations of a two-turbine wind farm show that the helix
approach leads to enhanced wake mixing with minimal power and thrust
variations.
