Influence of Spatially Varying Flow on the Dynamic Response of a Waterjet inside an SES

Michael R Motley,Brant R Savander,Yin L Young

doi:10.1155/2014/275916

Abstract

Surface Effect Ships (SES) are a promising fuel-efficient ship technology that typically carry most of their weight on an air cushion. To accommodate its shallow draft and slender side hulls and to absorb the high thrust and power required for high-speed applications, waterjets are typically used as the primary propulsion system. A waterjet typically has a flush mounted inlet and operates under complex three-dimensional flow conditions that result in highly nonuniform flows. The objectives of this work are to quantify the flow nonuniformity and the influence of unsteady cavitation on the response of an SES-waterjet system and to investigate the effect of flow nonuniformity and cavitation on the dynamic hydroelastic response of the rotor and stator blades. The results showed that as the flow advances through the pump, the ingested boundary layer from the bottom of the side hulls becomes increasingly nonuniform, particularly between the rotor and stator. The flow nonuniformity was shown to result in hydrodynamic load fluctuations and high side forces on the rotor and stator blades. The unbalanced blade loads lead to the generation of net upward forces on the pump casing and shaft. Flow nonuniformity also leads to unsteady cavitation and unsteady blade stresses and deformations.

Highlights

The Surface Effect Ship (SES) is a promising fuel-efficient advanced ship technology that typically carries approximately 80% of its weight on an air cushion
Failure to properly account for flow nonuniformity and unsteady cavitation can lead to under-conservative estimates of the pump performance and hydroelastic response
Validation of the computational fluid dynamics (CFD) predictions with model-scale experimental studies of cavitation tunnel studies of the axial flow waterjet Ax-WJ2 in uniform flow conditions is shown, followed by full-scale simulation of the T-Craft propelled by two Ax-WJ2 waterjets

Summary

Introduction

The Surface Effect Ship (SES) is a promising fuel-efficient advanced ship technology that typically carries approximately 80% of its weight on an air cushion. By lifting most of the vessel above the water, the wetted area and frictional resistance are drastically reduced at high speeds. To accommodate the shallow draft and slender side hulls of an SES and to absorb the high thrust and power required for high-speed applications, waterjets are typically used as the primary propulsion system. Waterjets offer many advantages, the low draft of an SES and interactions with the air cushion may lead to problematic air ingestion, especially when operating in high sea states. Other design trade-offs include reduced efficiency at low forward speeds (caused by increased wetted surface area and higher rotational speeds) and at off-design conditions (e.g., near the hump speed)

Objectives

Results

Conclusion