Hydrodynamic Optimazation Design And Nosie Analysis Of Ducted Contra-rotating Propeller

Energy conservation and environmental protection are two essential concepts in green ship design, and propellers as the major energy and noise source of the ships have been paid more and more attention of researchers. Ducted contra-rotating propeller(DCRP) is an effective combination of ducted propeller and contra-rotating propeller with the advantage of higher efficiency, larger thrust and lower noise, few studies on which have been conducted. On the basis of a conventional 19A/Ka4-55 ducted propeller model, an optimization design method of DCRP is achieved according to cascade theory in this paper. The hydrodynamic performance of the DCRP is predicted with viscous CFD-based software CFX, and noise analysis is conducted using Actran, based on Lighthill analogy variational formulation FEM method. Comparisons with single-rotor ducted propeller(DSRP) on hydrodynamic and noise performance are also made.Firstly, several practical configurations of DCRP are presented in this paper. For the lack of research on DCRP, respective features of ducted propeller and contra-rotating propeller are introduced, along with the studying methods of hydrodynamic performance and the development tendency. Noise prediction technique of marine propeller is also summarized here.Secondly, the open water performance of a 19A/Ka4-55 DSRP model is obtained using viscous CFD method whose validity is tested by being compared with the experiment results. Sharing similarity with turbine on the configuration and internal flow pattern, a DCRP is initially designed based on cascade theory as well as a DSRP model, with which the hydrodynamic performance is contrasted.Thirdly, this paper determines the cause of the unsatisfactory performance of initially designed DCRP. Pitch compatibility between the forward propeller and the aft one is studied with two approaches of equal tangential induced velocity at exit and equal work ratio, using rotational speed adjustment. The periodical phase change between the forward and the aft propeller result s in large amplitude of force and torque fluctuation, namely large exciting force, and base upon which the influence of different blade number is studied.Finally, non-cavitation noise performances of both DCRP and DSRP with uniform and non-uniform inflow are respectively analyzed using Lighthill analogy variational formulation FEM method. The frequency-domain acoustic source is obtained using FFT technique on time-domain velocity field from unsteady computation. The characteristics of sound pressure level(SPL) frequency spectrum, noise attenuation with distance and advanced coefficient, SPL directivity, acoustic source are studied.A hydrodynamic design method of a new-type propulsor is presented in this paper as well as its noise performance analysis, shedding light on the further research in this area.