Optimum Propeller Positioning and Sizing for Underwater Vehicles

The study investigates the influence of the propeller diameter and longitudinal position on the overall propulsion efficiency of axial-symmetric underwater vehicles, by means of high-fidelity viscous flow simulations. Firstly, we augment the classical problem of choosing the optimum propeller diameter, including the variable longitudinal clearance between the propeller and the tail of the hull. Secondly, we further generalized the problem, allowing for the variation of self-propulsion coefficients, namely thrust deduction, wake fraction and relative-rotative efficiency. A different nominal wake would generally lead to a different propeller designs, adapted to that wake, with a different open water efficiency. The overall propulsion efficiency, combining the hull efficiency with the open water propeller efficiency, is a result of both changes. For the first time the propeller-hull interaction has been systematically analyzed by means of virtual tests, using RANSE solvers with transitional turbulence models and the effect of the interaction has been propagated all the way down to the optimum propeller selection to estimate the overall propulsion efficiency.