The Relationship Between Vortex Pairings and Velocity Deficit Recovery in a Wind Turbine Wake

The rapid recovery of a velocity deficit in a wind turbine wake was studied using unsteady simulations of Navier-Stokes equations. The results indicate that as the tip speed ratio (TSR) increased, the velocity deficit in the far-wake region was reduced while the deficit in the near-wake increased. This was caused in part by the difference of tip vortex behaviors; as the TSR increases, the distance between vortices narrows. This narrow interval can accelerate the pairing of vortex sheets, producing larger structures and accelerating the recovery of the velocity deficit.