Development of an optimisation process for pre-swirl stator designs

A pre-swirl stator can reduce a ship's propulsion power up to 7%, saving $84.000 and 540 MT CO2 a year for an average cargo ship. The pre-swirl stator changes the wake field, which allows for the propeller to generate the same thrust at a lower rotation rate. This reduces rotational kinetic energy losses in the wake. An interface was developed to optimise the stator geometry, operating in axial inflow. A Single Objective Genetic Algorithm was tested with two sets of design parameters, for different generation sizes and number of generations. The stator and propeller were simulated separately with a Boundary Element Method flow solver and coupled using local wake fields. Optimal designs showed a power reduction of 5.3-6.5\%. The main design parameters were the pitch and the chord at the hub. Comparison of the flow field of a propeller with and without pre-swirl stator showed a difference in both tangential and axial forces, which increased over a large part of the propeller blade, while the pressure distribution was changed mainly at lower radial sections. Comparison with a viscous flow solver showed similar results, differences were found in the prediction of the friction force and the power.