Propeller nozzles design using viscous codes and optimization algorithms

Marine propellers design requirements are always more pressing and the application of unusual propulsive configurations, like ducted propellers with decelerating nozzles, may represent a valuable alternative to fulfil stringent design constraints. If accelerating duct configurations were realized mainly to increase the propeller efficiency in highly-loaded conditions, decelerating nozzles sustains the postponing of the cavitating phenomena that reflects into reduction of vibrations and radiated noise. The design of decelerating nozzle, unfortunately, is still challenging. No extensive systematic series are available and the design relies on few measurements. On the other hand, viscous flow solvers appear as reliable and accurate tools for the prediction of complex flow fields. Hence, in the present paper the opportunity to use CFD as a part of a design procedure based on optimization, by combining a parametric description of the geometry, the OpenFOAM solver and a genetic type algorithm in the ModeFrontier environment, is investigated. Design improvements for both accelerating and decelerating ducts are measured by comparing the performance of the optimized geometries with those of conventional shapes available in literature.