Pre- and post-swirl fins design for improved propulsive performances

Pre- and post-swirl fins-based energy-saving devices (ESD) are designed to improve the propulsive performances of a twin-screw ship. To this aim, BEM and RANSE calculations are employed. Depending on the application, a simple actuator disc model (post-swirl) with radially varying load or a combined BEM/RANSE method for self-propulsion prediction (pre-swirl) are required. Both the approaches are included in a framework for a design by optimization, where systematic variations of the ESD geometry are used to explore the design space and maximize the energy-saving effect of the devices. Considering the particularity of the case selected for the study, results show encouraging improvements that reach a promising 5% in the case of the combined action of both devices.