Flow Improving Devices For Marine Propulsers. Concept Design Study

Abstract

Flow-improving devices (FIDs) are used the most effectively for the reduction of noise and vibration induced by a propulsor. These devices may also increase the efficiency of a propulsor and in some cases should be considered and designed as a part of an Integrated Propulsor, for example, non-axis symmetrical ducts. The FIDs may be naturally subdivided into two types: active and passive. The active ones are powered, such as the devices for local suction and injection of water, air, or polymer solutions, devices for local heating, etc. Passive FIDs are the ones that, generally speaking, use the power of inflow. Sometimes the power is lost unless not used for flow improvement, this is how the energy saving is achieved. Many passive FIDs are based on the effect of longitudinal vortices working in a boundary layer of a hull. The traversal velocities induced by these vortices redistribute the longitudinal velocities in a boundary layer of a hull and thus affect the circumferential non-uniformity of a propeller's inflow. The core of several new solutions of FIDs proposed in this document is a non-axis-symmetrical ring wing placed upstream of the propeller between the propeller and the appendages. Several arrangements are considered in which the Ring Wing functions differently but always delivers a positive effect on the Propulsor.