Experimental investigation of propeller wake evolution by means of LDV andflow visualizations

An experimental investigation of the propeller wake has been performed in a cavitation tunnel using LDV and flow visualizations. The objective is the hydrodynamic and geometrical characterization of the wake flow field and it s downstream evolution features. Implications of the physical aspects for w ake modeling are also highlighted. The viscous blade wake, originating in t he boundary layer on the blade surfaces, the trailing vortex sheets, due to the radial gradient of the bound circulation, as well as the turbulence di stribution are identified at the trailing edge and followed. The near-wake geometry is quantitatively determined describing the progressive bending of the blade wake sheers, the slipstream contraction and the tip vortex traje ctory. Furthermore, the effects of turbulent diffusion and viscous dissipat ion, which cause a rapid space-broadening of the velocity gradients in the trailing-edge wake, are examined. Insights into the viscous interaction bet ween blade flow and roll-up process in the tip region are also proposed. Fi nally, the onset and development of the slipstream instability leading to t he breakdown of the vortices system in the far wake are studied also by mea ns of visualizations in incipient cavitating flow conditions.