CPP propeller cavitation and noise optimization at different pitches with panel code

D. Bertetta, S.Brizzolara, S.Gaggero, M.Viviani (Genoa University), L.Savio (Norwegian University of Science and Technology)

The propeller design has evolved significantly in the last years, with the introduction of numerical methods which can provide an ever improving assessment of the propeller characteristics, considering the propeller on-stationary functioning and cavitating behavior, not only in correspondence to the usual design conditions, but also to off-design conditions, hardly captured by conventional design methods. Modern propellers design involves many different requirements, not limiting to the maximum efficiency, but extended also to the propeller cavitating behavior and, more and more, to its side effects, in terms of radiated noise and pressure pulses. This is evident with the ever increasing demand for improvement of comfort onboard and concerns about radiated noise problems, especially in proximity of protected areas.

In the present paper a multi-objective optimization, carried out in the framework of EU funded project SILENV—Ship-oriented Innovative solutions to reduce Noise & Vibrations, of an existing CPP propeller for a RO–RO ferry is presented. The optimization activity is particularly challenging since two very different working conditions (maximum speed and low speed) are contemporarily considered, in order to test the capabilities of the design procedure mentioned above. The optimization was carried out in modeFRONTIER with a genetic algorithm in order to obtain a new propeller geometry able to reduce back cavitation and face cavitation, keeping constant the numerically computed delivered thrust in both working conditions. Numerical results are validated by means of an experimental campaign, testing both the original and the optimized geometry in terms of cavitation extent and radiated noise. Experimental results confirm the numerical predictions, attesting the capability of the method to assess propeller functioning characteristics, thus representing a very useful tool for the designer in correspondence of challenging problems.