Abstract
This paper concludes a series on the formation and development of the near-wake of a model horizontal-axis wind. The three-dimensional mean velocity and turbulence fields were obtained at six axial locations within two chord lengths of the blades for three operating conditions: stalled flow over the blades, close to optimum performance, and approaching runaway. Here we concentrate on the tip and hub vortices. For the second and third conditions, the hub vortex quickly becomes a sheet of vorticity spread over the cylindrical centrebody. It is suggested that the ‘trailing vorticity’ at the hub is formed by the skewing of the circumferential vorticity in the upstream boundary layer as it encounters the blades, so that the ‘bound’ vorticity of the blades simply passes through the centrebody surface. The tip vortices, which were shown in Part 2 to contain increasing amounts of angular momentum as the tip speed ratio increases, are associated with large variations in all velocity components and high levels of turbulence. The pitch of the helical tip vortices decreases with increasing tip speed ratio.
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