A study on the numerical prediction of propellers cavitating tip vortex

The problem of the tip vortex cavitation inception is a matter of increasing interest. Main reason for this is that, despite being, generally, not erosive and not influent on the propeller mechanical characteristics, the cavitating vortex dynamics may play a significant role in the propeller radiated noise. In the present work, a thorough analysis of the capability of a commercial RANS solver in conjunction with the Schnerr-Sauer cavitation model to predict the tip and the tip leakage vortex cavitation (with particular attention to their inception) for a conventional and two ducted propellers respectively, is presented. Considering at first a conventional CP propeller, a comprehensive analysis of the effect of the various parameters (e.g. mesh characteristics, number and size of nuclei in the numerical calculations) on the computed results is reported, together with a comparison with the experimental measurements carried out in a cavitation tunnel. This analysis allows to stress the capabilities of RANS computations to correctly predict tip phenomena and to provide guidelines in order to obtain reliable numerical results, having in mind the necessity of a compromise between calculation accuracy and computational time, essential in the case of a systematic application of the presented approach for design purposes. Furthermore the calculations are repeated also for two propellers in decelerating duct and the satisfactory results obtained demonstrate the capability of the proposed approach to correctly rank two slightly different geometries also for this more complex and challenging case. (C) 2014 Elsevier Ltd. All rights reserved.