Integrated design of asymmetric aftbody and propeller to maximize energy efficiency
Author Rueda, L. and Dang, J.
Title Integrated design of asymmetric aftbody and propeller to maximize energy efficiency
Conference/Journal RINA Energy Efficient Ships, Rotterdam, The Netherlands
Month November
Year 2015

Summary
With the implementation of the EEDI, energy saving and emission reduction of ships, especially merchant ships, become more and more important. To achieve high efficiency and low emissions, recently Energy Saving Devices (ESDs) have been re-studied and installed to many ships, both new buildings and also retrofits. Due to the fact that most ESDs are fitted in the wake field however, the performance of the ESDs is influenced by scale effects.

Distinguished from the ESDs where extra ‘appendages’ have to be added in front of and/or behind a propeller, a ship with asymmetric aftbody can also change the flow towards the propeller, however without appendages. The wake with pre-swirl generated by an asymmetric aftbody is in general more uniform than that by an ESD and with almost no penalty on the ship’s resistance.
In this paper, the optimization procedure to improve the total propulsive efficiency of a ship with asymmetric aftbody is discussed first. CFD RANS-BEM coupling technique is elaborated thereafter to evaluate the powering performance of the optimised symmetric and asymmetric ships.

Furthermore, comparative model tests for both designs have been carried out to verify CFD results. Finally, this paper has discussed the scale effects on the propulsive performance of the asymmetric ship, which confirms that more than 6% extra gain in efficiency can be obtained by using asymmetric aftbody at full scale.

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