Design of PBCF energy saving devices using optimization strategies: A step towards a complete viscous design approach

The need of improving propulsive efficiency continuously encourages the development of energy saving devices, the understanding of their underlying principles and the validation of their effectiveness. In this work, a design by optimization of Propeller Boss Cap Fin (PBCF) devices is carried out using Computational Fluid Dynamics analyses. RANS Equations, solved by using the OpenFOAM library, are applied in an automatic design approach involving a parametric description of the main characteristics of PBCFs and an optimization algorithm. The optimization is carried out with multiple purposes: identify a reliable design strategy necessary to customize the PBCF geometry based on the propeller functioning and, by exploiting the systematic calculations carried out in the framework of the optimization, evaluate the influence of alternative configurations and of main geometrical parameters in achieving higher efficiency. The use of high-fidelity RANS calculations allows confirming the decrease of the hub vortex strength, the reduction of the net torque and the influence of the additional fins on blades performance as the major contributors to the increase of efficiency. Results of detailed analyses of optimal PBCF configurations show model scale increases of efficiency of about 1%, which can reach the outstanding value of 4% in the case of a rather unrefined propeller design.