Performance analysis of ducted marine propellers. Part II - Accelerating duct

This paper completes the work presented in the companion paper [Bontempo et al., Appl. Ocean Res., 58 (2016) 322-330] by presenting the investigation of the flow around a propeller ducted with a so-called accelerating duct. To this aim, both the axial momentum theory and a nonlinear actuator disk method are used. The straightforward application of the first approach reveals that if the duct and rotor thrusts are concordant, then a beneficial effect on the propulsive efficiency can be readily obtained by enclosing a propeller in an accelerating duct. When the more advanced nonliner actuator disk method is applied to verify the outcomes of the axial momentum theory additional information on the performance of the device are obtained. Moreover, the nonlinear actuator disk method is also employed to investigate, through experimental design techniques, the effect of the key geometrical parameters of the duct onto the efficiency and robustness of this kind of propulsive system. In particular, it has been found that a propulsive efficiency gain can be achieved through a duct thickness, camber and chord increase, and through an incidence decrease.