Design of retrofit devices using CFD, validated with wind tunnel tests

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Description/Abstract

The energy efficiency design index (EEDI) currently under development will lead to high emission ships being taxed heavily in the future. As a result, many possible design solutions to increase the efficiency of high powered ships are currently being investigated. However, existing ships must rely on engine room systems upgrade or the use of retro-fit devices.

The aim was to seek a low cost approach to solve the challenge of how to improve the energy efficiency of existing ships. To demonstrate this approach a specific oil tanker hull form was studied and future novel methods of achieving a gain in propulsive efficiency were considered.

Wind tunnel and towing tank testing are used, in conjunction with opensource computational fluid dynamics modelling, to analyse the wake field changes caused by the devices. Changes in efficiency are assessed using the propeller efficiency modelled with a blade element momentum code. A testing procedure, explained in terms of methodology with objective justification for improvements has been developed. This procedure successfully detects changes in propeller efficiency at model scale due to devices, and thus provides a route to evaluate a wide variety of devices.

Preliminary results suggest that gains in efficiency of at least 3% could be obtained with simple vanes and 2% for pre-swirl ducts. These values could be greatly increased through further optimisation of device size, geometry, position and angle of attack.