A new insight in the propeller wake by means of PIV

A propeller wake investigation is carried out in a cavitation tunnel using PIV technique. A multigrid adaptive cross-correlation algorithm is used for the image analysis to obtain high spatial resolution The contributions of the viscous wake, originated by the boundary layers on the blades, of the trailing vortex sheets, as well as of the vorticity distribution, are resolved and discussed for different revolution blade angles. The near wake flow is characterised by strong deformations, due to the bending of the blade wake sheets, to the contraction of the slipstream and to the trajectory of the tip vortex. Furthermore secondary tip vortex structures are pointed out while the turbulent diffusion and the viscous dissipation rapidly lead to broadening and decay of the trailing edge wake.