Some Experimental Results of Tests of a Low-Speed, Waterjet Propulsion System

Abstract

Experimental data for static and dynamic performance of a 16J-in.-diam prototype waterjet propulsion system are presented. This system is designed for propulsion of a hydrofoil craft to operate in displacement mode at 9 knots, 175 hp, and be direct-driven at 2500 rpm. These specifications dictate low head and high throughflow pump characteristics and corresponding specific speeds and suction specific speeds exceeding 26,000 and 21,000, respectively. The single-stage axial-flow pump designed to perform this task required particular attention to correlation of pump parameters with cavitation criteria to override some of the limitations of current axial-flow pump technology. Performance results of the prototype unit indicate that useful thrust is not difficult to attain, but that the flow-choking and head-reducing influence of cavitation phenomena rapidly decreases over-all system efficiency. Evidently more sophisticated hydrodynamic theory to rationalize the balance between bladiiig losses and blading total static pressure rise is required to maintain better efficiency levels. Preliminary observations and performance data presented here indicate some of the problems associated with the design of waterjet propulsion systems in which achievement of useful propulsive efficiency is dependent 011 the ability of the propulsor to operate with high axial velocities.