A comprehensive design method is applied to design of counter-rotating propellers (CRP). A numerical nonlinear optimization algorithm is first used for design of each propeller. This approach represents a blade by B-spline geometry and the design variables at the location of the vertices of the B-spline polygon determine the optimal blade shape. The nonlinear optimization method aims at minimizing the torque for a given target thrust with constraints, e.g. the minimum pressure constraint for a fully wetted propeller or maximum allowed cavity area for a cavitating propeller. Then the interaction of the designed propellers and a given pod including the viscous flow field around the two propellers is analyzed by coupling a vortex-lattice method (VLM) with a Reynolds-Averaged Navier-Stokes (RANS) solver. The analysis determines a new inflow for a new design of propellers. The procedure of the design and interaction analysis finishes when the propeller thrust converges within a certain tolerance. Finally, the designed propellers are compared with the original propellers.

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