Propeller Wake Evolution Analysis by LDV

A propeller wake investigation is carried out using LDV in a cavitation tunnel. The analysis is focused on the geometrical and hydrodynamic features of downstream wake evolution because the model arrangement in the test section enables slipstream to evolve freely for many diameters. The viscous blade wake, originated by the boundary layer on the blade surfaces, the trailing vortex sheets, due to the radial gradient of the bound circulation, as well as the turbulence distribution are resolved in the trailing edge flow and discussed The near wake geometry is characterized by marked deformation processes, due to the bending of the blade wake sheets, the contraction of the slipstream and the trajectory of the tip vortex. Furthermore, the turbulent diffusion and the viscous dissipation lead rapidly to marked broadening and decay of the trailing edge wake. The roll-up and viscous effects in the spiraling process are also pointed out. Finally, the slipstream instability and the breakdown of the hub and tip vortices system are outlined also by means of flow visualizations.