Pre-swirl energy saving device in marine application

This paper covers topics of energy saving device (ESD) with application to marine propulsors. The form of ESD, considered in this paper, consists of fixed lifting foils mounted in front of the screw propeller (the pre-swirl stator/guide vanes). An algorithm for designing propulsion systems, consisting of guide vanes and screw propeller, is presented. The proposed method relies on hybrid lifting line (guide vanes)-lifting surface (screw propeller) vortex model. Additionally, an analysis method for such systems is also presented. It utilises lifting surface model for guide vanes as well as for screw propeller blades. Accuracy of the proposed method is notably lower in comparison with CFD calculations, however, the former is substantially faster and at the same time capable of providing accuracy sufficient for practical application. Further, the entire process of design and analysis is presented on the example of Nawigator XXI ship. The designed propulsion system, consisting of propeller CP753 and pre-swirl stator ST002, was manufactured and tested in model scale. Model tests revealed increased efficiency by 4% in the design point in comparison with with the Nawigator’s original propeller CP469. Finaly, model scale experimental results, conducted in Ship Hydrodynamics Division of CTO Gdansk, are compared with numerical predictions.