D34.1 - Report on BEM model improvement

The results of the development and validation of a hydrodynamics model for the computational analysis of marine propellers are presented. The activity is performed in the framework of WP34 of the STREAMLINE Project and the present report is written in fulfilment of Deliverable D34.1. Aim of the work is to enhance the accuracy and the range of applicability of an existing inviscid-flow propeller model based on a Boundary Element Method (BEM). Model improvements primarily include (i) the capability to describe trailing vorticity shedding and the resulting induced velocity field, (ii) the inclusion of suitable models to capture viscosity effects on blade loading as well as on global propeller performances, and (iii) the prediction of blade cavitation and its harmful consequences. Next, the generalization of a BEM for single propellers to analyse complex configurations where a bladed screw hydrodynamically interacts with surrounding bodies is addressed. The proposed approach is valid to analyse configurations like propeller-rudder, podded propellers and contra-rotating propellers. Theoretical and computational aspects of the proposed models are briefly described, whereas details of verification and validation studies are presented. Numerical results of single propeller flow calculations are carried on by considering two test cases: the INSEAN E779A model propeller, and the STREAMLINE WP21 baseline propeller. Next, validation studies of the BEM model for multi-body configurations are performed by considering the SSPA P1356/P1357 contra-rotating propeller system. In all case studies addressed, numerical results from the present BEM model are compared with available experimental and computational data. As a result of verification and validation studies it may be concluded that the proposed BEM model provides a useful computational tool to provide propeller hydrodynamics predictions characterised by an appealing trade-off between accuracy and computational costs. Hence, the hydrodynamics model by BEM is adequate to be applied to design and numerical optimization tasks planned in the STREAMLINE project.