A DPIV study of the trailing vortex elements from the blades of a horizontal axis wind turbine in yaw

Digital particle image velocimetry (DPIV) has been used in a wind tunnel study to measure the velocity field of the trailing vortices from the blades of a horizontal axis wind-turbine (HWAT) in yaw. The creation of the trailing vortex circulation is shown to vary as a function of the phase angle of the rotor and the angle of yaw between the wind and turbine rotor. The strength of the convecting vorticity was also shown to vary with time. The initial formation of the vortex is shown determined by the flow expansion angle while in yawed flows the developing vortex is then influenced by the vortex sheet shed from the inboard blade trailing edge. This interaction is shown to significantly affect the roll up of the tip vortex.