A Stereo-PIV Investigation of a Propeller's Wake behind a Ship Model in a Large Free-surface Tunnel

Abstract

An experimental investigation of a five blade MAU propeller wake behind a Series 60 Cb=0.6 ship model has been performed using Stereo Particle Image Velocimetry (Stereo-PIV) in a large free-surface cavitation tunnel. The investigation of the wake and its evolution during propeller revolution and at different longitudinal stations has pointed out the capability of Stereo-PIV in resolving the complex flow field with great accuracy. As a first step of this investigation, a systematic measurement analysis has been done to find the best angle between the two cameras. The blade viscous wake, developing from the blade surface boundary layers; the trailing vortex sheets, due to the radial gradient of the bound circulation; and the velocity fluctuation distributions are identified and discussed. The complex interaction between the hull wake and propeller is described through the evolution of the mean velocity components and the vorticity fields. 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. Comparison with LDV measurements shows a substantial agreement between the two techniques.