Experimental Investigation of the Propeller Wake at Different Loading Conditions by Particle Image Velocimetry

An experimental investigation of the propeller wake in a cavitation tunnel has been performed using particle image velocimetry (PIV). A PIV image analysis algorithm implementing iterative window offset and stretching has been adopted. The main characteristics of the propeller wake at different loading conditions have been pointed out by using phase sampling techniques. Longitudinal evolution of the blade viscous wake, developing from the blade surface boundary layers, of the trailing vortex sheets, due to the radial gradient of the bound circulation, is discussed up to 1 diameter downstream. In the near field the effects of turbulent diffusion and viscous dissipation, which cause a rapid space broadening of the velocity gradients in the trailing edge wake, are also examined. In the far wake the development of the slipstream instability and the breakdown of the hub and tip vortices are outlined.