Towing Tank Model Tests for Propulsive Performance Analysis of a Waterjet-Propelled Amphibious Vehicle

Abstract

The present study concerns a series of model tests in a towing tank on waterjet propulsive performance. The test model was an armored vehicle consisting of a box-shaped hull, two waterjets, a bow flap, and a trim tab. As per the powering prediction procedure of high-speed vessels, resistance tests, waterjet system tests, and self-propulsion tests were performed. The Froude number based on the characteristic length and advance speed for the model tests ranged from .981 to 1.178. Bollard pull tests were also conducted to investigate the interaction between the hull and two installed waterjets and to validate the flow rate estimation. In the self-propulsion condition, the dry transom and nozzle end modification changed the interaction efficiency. The waterjet reduced the vehicle trim in the self-propulsion condition, owing to the nozzle exit flow onto the trim tab. Introduction Waterjet propulsion systems have been widely used in marine vessels, thanks to its advantages of low cavitation in high loading, safe operation in shallow water, and good maneuverability at low advance speed (Allison 1993). However, the propulsive performance of waterjets is a complicated problem and hard to analyze. The extrapolation method for the powering performance prediction of waterjet-propelled vessel is suggested by the International Towing Tank Conference (ITTC) (ITTC 2011), but it is less comprehensive than that of the conventional ship with screw propellers (ITTC 2017a), as test institutions for waterjet-propelled vessels are scarce and test methodology is not standardized (Altosole et al. 2012).