.

Abstract

The main objective of present study is to investigate the flow characteristics of complex flow around a marine propeller using a two-frame PIV (Particle Image Velocimetry) technique. The rotating propeller of 4 blades was tested in a cavitaion tunnel without any wake screen. For each of 9 different blade phases from 0o to 80o, one hundred and fifty instantaneous velocity fields are measured. They are ensemble averaged to study the spatial evolution and vortical behaviors of the propeller wake in the region ranging from the trailing edge to one propeller diameter (D) downstream location. The phase-averaged mean velocity shows that the trailing vorticity is related to radial velocity jump, and the viscous wake is affected by boundary layers developed on the blade surfaces and centrifugal force. Both Galilean decomposition method and vortex identification method using swirling strength calculation are very useful for the study of vortex behaviors in the propeller wake region. The slipstream contraction occurs in the near-wake region up to about X/D = 0.53 downstream. Thereafter, unstable oscillation occurs because of the reduction of interaction between the tip vortex and the wake sheet behind the maximum contraction point.