Publications

Rapidly recovering wind turbine wakes with dynamic pitch and rotor speed control

Brown, Kenneth B.; Houck, Daniel; Maniaci, David C.; Westergaard, Carsten

Advances in wind plant control have often focused on more effectively balancing power between neighboring turbines. Wake steering is one such method that provides control-based improvements in a quasi-static way, but this fundamentally does not change the downstream wake deficit and thus, can only provide limited improvement. Another control paradigm is to leverage the turbine as a flow actuator to dynamically excite unstable modes in the wake, thereby producing accelerated wake breakdown and recovery. Taking a more applied approach than some studies in the wake instability area, this article investigates the use of dynamic wake control (DWC) from two existing turbine control vectors, blade pitch and rotor speed, to incite rapid breakdown of the tip vortex structures. Both control vectors can be dynamically manipulated to make a significant difference on the wake structure and breakdown. The mid-fidelity free-vortex wake method (FVWM) used below allows a thorough search of the parametric space while still capturing the essential physics of the mutual inductance instability. The parameters for investigation include the frequency, amplitude, and phase of the harmonic forcing for both control vectors. The output from the FVWM is the basis for a Fourier stability analysis, which is used to pinpoint and quantify candidate forcing strategies with the highest instability growth rates and shortest near-wake lengths. The strategies, including dynamic rotor speed, blade pitch, and a novel tandem configuration, work to augment the initial tip vortex instability magnitude, leading to near-wake length reductions of greater than 80%, though without considering inflow turbulence. Analysis is provided to interpret these predictions considering the presence of inflow turbulence in a real atmosphere.