Comparison of different propeller boss cap fins design for improved propeller performances

The performances of different Propeller Boss Cap Fins devices, designed with the aid of a Simulation Based Design Optimization approach, are analysed and compared. A novel configuration, i.e., a PBCF inside a nozzle, is investigated in an effort to mitigate possible side effects of conventional Propeller Boss Cap Fins, such as secondary vortical structures from the fins tip, increased pressure pulses and radiated noise, without excessive worsening of the beneficial effects (increased propulsive efficiency) provided by this energy saving device. Detailed analyses reveal, instead, the destabilizing effect of the hub vortical structures on the blade tip vortex evolution, determining a substantial increase of the radiated noise of this type of propulsors.