In this paper, a systematic method to design marine ducted propellers is presented for a given duct shape and design conditions to achieve the highest efficiency while avoiding cavitation. The duct is solved by the 2D-axisymmetric Reynolds-Averaged Navier-Stokes (RANS) method and the propeller is designed and analyzed by potential flow methods (lifting line method and vortex lattice method). The initial propeller is designed based on the optimal loading from the RANS/lifting line model interaction method. A nonlinear numerical optimization method is used to refine the propeller in the effective wake (defined as the difference between the total velocity and the propeller induced velocity), with constraints to avoid cavitation for a given cavitation number. Each design is analyzed in a previously-developed and validated RANS/vortex lattice method interaction model to check if the optimization objective is achieved.


In the past, different methods have been developed to analyze the complex flow interaction between the propeller and the duct. Kerwin et al. (1987) applied the vortex lattice method (VLM) on the propeller and the boundary element method (BEM, more commonly known as the panel method) on the duct. Lee and Kinnas (2006) applied the panel method on both propeller and the duct, which was improved by Kinnas et al. (2015) and Kim et al. (2018) by including the duct-induced velocities in a pseudounsteady wake alignment scheme (full wake alignment scheme, or FWA). Du and Kinnas (2019) applied a flow separation model with the panel method on a ducted propeller with a blunt trailing edge duct. Hoekstra (2006) and Majdfar et al. (2017) conducted the full-blown Reynolds-Averaged Navier-Stokes (RANS) simulations on ducted propellers. Tian et al. (2014) and Bosschers et al. (2015) used a hybrid RANS/potential flow method to calculate the open water characteristics of ducted propellers, in which the propellers are represented as distributed body forces in the RANS simulation and the strength of the body force is either from the vortex lattice method or from the panel method. In Tian et al. (2014), the effect of the duct on the propeller is considered through an effective inflow, namely the effective wake, which is defined as the difference between the total velocity and the propeller-induced velocity. Open water tests of a four-blade propeller with a square tip operating with a duct with sharp trailing edge (propeller Ka4–70 and Duct 19Am, as shown in Fig. 1) were carried out by Bosschers and van der Veeken (2008) to provide valuable experimental data to validate several numerical models mentioned above.

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