Practically applicable devices for blocking the gap flow of a horn rudder to reduce rudder cavitation and their verification through numerical simulations

Abstract

Rudder cavitation causes serious damage to the rudder and affects the safety and cost-effectiveness of a ship. In recent applications, a semicircular prismatic bar protruding beyond the concave surface of the horn facing the gap, located along the center-plane of the rudder, has been used to lessen the gap flow between the horn and the movable portion of the rudder system. Previous numerical studies with this single bar indicate that it can noticeably reduce rudder cavitation. In the present study, a pair of bars for blocking the vertical gaps, which are attached symmetrically to the center-plane on opposite convex surfaces of the movable portion, is suggested for circumventing the difficulties that arise in the practical application of single centre bars. Placed near the outer edges of the gap, the bars are are easily accessible at the maximum rudder angle to allow simple installation during routine ship maintenance. An additional blocking disk is inserted on top of the pintle block, blocking the horizontal gaps. Threedimensional computations are conducted with these combined devices and the results show that the devices are remarkably efficacious in reducing rudder gap cavitation.

A numerical simulation for reduction of rudder cavitation with gap flow blocking bars

“…A substantial reduction in gap clearance can raise serious technical difficulties in the rudder installation processes and studies have been done to moderate the gap cavitation by other means. Rhee and Kim (2008) suggested a cam device for gap flow blocking and Paik, et al(2008), Rhee, Lee, Lee and Oh (2010), and Seo, Lee, Kim and Oh (2012) demonstrated that the device can suppress the gap cavitation through model experiments and computations. Seo, Lee, Oh and Kim (2010) showed that the jet blowing system devised for a high-lift rudder can be utilized in order to mitigate the gap cavitation of a rudder with a small amount of flow injection in the reverse direction.…”