Measurements of the rudder inflow affecting the rudder cavitation

The main objective of present study is to examine the characteristics of the complex rudder inflow(propeller slipstream) against the rudder cavitation using visualization technique. The rotating propeller of 6 blades and the semi-spade rudder are set in a medium-size cavitaion tunnel with a uniform flow condition. The rudder distorts the angle-of-attack (AoA) or incident angle to the leading edge of the rudder blade. Several methods such as uniform stream line, time-averaged velocity field and locally sampled area are proposed to analyze the AoA and show similar AoA values of 5–7° at the region of no rudder and no propeller trailing vorticity effects. However, it increases to 20° by those effects as the inflow comes to the rudder. From the AoA analysis the cavitation durability is found to be about 7° in terms of the rudder angle. Cautious access is additionally necessary to introduce a reasonable safety against those cavitation phenomena that would significantly influence the durability of the movable part.

► The rudder inflow between propeller and rudder is successfully measured with PIV technique.
► Three kinds of methods are introduced in analyzing rudder incident angle.
► The rudder incident angel is 5–7° in the region of no propeller trailing vorticity and no rudder effects.
► Rudder cavitation durability is discussed in terms of the rudder incident angle.