Design of pumpjet propulsors using RANS-based multi-objective optimization

The design of linear pumpjets is addressed through a simulation-based design optimization approach based on RANS analyses in the case of rotor/stator (i.e., post swirl) configurations, characterized by 5 rotor blades and 5 or 10 stator blades. The optimal geometries from a multi-objective optimization process aimed at maximizing the propulsive efficiency at the lowest possible cavitation inception index are compared to a reference ducted propeller with decelerating nozzle, which served as baseline during the activity. A significant increase of propulsive efficiency with a reduced risk of cavitation is observed. Fully unsteady cavitating analyses are used to assess the reliability of the design activity, which is necessary build upon some simplifying assumptions (i.e., rotor/stator coupling through a mixing plane) needed for an affordable numerical process. Detached Eddy Simulations (IDDES) are finally carried out to highlight, in addition to the performance improvements provided by the pumpjets, also the influence of the rotor/stator/nozzle interaction on the vortical structures shed by the propulsors.