On the Design and Analysis of Pre-Swirl Stators for Single and Twin Screw Ships

Fuel saving and emission reduction are main drivers for the current strong developments in the improvement of Marine Propulsor Technology. For this reason, and because of improved design and analysis tools, we see a renewed interest in Energy Saving Devices (ESDs).
This paper focuses on the pre-swirl stator device providing the possibility to reduce the rotational losses incurred by the propeller. The pre-swirl stator gives only a portion of the total gain to be attained, however. Additional features could be employed, particularly in high-block ships, such as a rational Van Lammeren L-J duct.
The general mechanism of pre-swirl stators to reduce fuel consumption is explained and the design problem is stated. Subsequently, the tools deployed for analysis and design of pre-stator – propeller configurations are discussed with special attention for viscous effects.
An example of a pre-swirl stator for a single screw container vessel is worked out using lifting line theory. A full viscous analysis is illustrated with our RANS code ReFRESCO. The use of a potential flow BEM code is then illustrated for a first assessment of propeller-stator performance. Estimates are also made in the paper of the energy saving potential of pre-swirl stators applied to twin screw ships.