The interaction of helical tip and root vortices in a wind turbine wake

Michael Sherry (1) , Andras Nemes (1) , David Lo Jacono (2) , Hugh M. Blackburn (1) , John Sheridan (1)

1 Department of Mechanical and Aerospace Engineering [Victoria]]
2 IMFT - Institut de mécanique des fluides de Toulouse

Analysis of the helical vortices measured behind a model wind turbine in a water channel are reported. Phase-locked measurements using planar particle image ve- locimetry are taken behind a Glauert rotor to investigate the evolution and breakdown of the helical vortex structures. Existing linear stability theory predicts helical vortex filaments to be susceptible to three unstable modes. The current work presents tip and root vortex evolution in the wake for varying tip speed ratio and shows a breaking of the helical symmetry and merging of the vortices due to mutual inductance between the vortical filaments. The merging of the vortices is shown to be steady with rotor phase, however, small-scale non-periodic meander of the vortex positions is also ob- served. The generation of the helical wake is demonstrated to be closely coupled with the blade aerodynamics, strongly influencing the vortex properties which are shown to agree with theoretical predictions of the circulation shed into the wake by the blades. The mutual inductance of the helices is shown to occur at the same non-dimensional wake distance.

Mots clés: Wind turbine; Vortices; Wake

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]

Michael Sherry, Andras Nemes, David Lo Jacono, Hugh M. Blackburn, John Sheridan. The interaction of helical tip and root vortices in a wind turbine wake. Physics of Fluids, 2013, vol. 25, pp.1-16. ⟨10.1063/1.4824734⟩. ⟨hal-00913622⟩