Abstract
During maneuvers, propellers’ operation differs from their design due to strong modification of the wake field with respect to the straight-ahead motion. The consequent modification of the loads overstresses the mechanical components of the shaftline, exacerbates propeller side effects and worsens overall efficiency. Therefore, the analysis of these situations in the early design phase is pivotal to increase the operation capabilities and safety at sea. This task relies on novel tools capable to accurately predict the complex flow field that develops past the hull and the propeller loads. Since the solution of the fully coupled problem with the rotating propeller by viscous flow solver is impractical for routine applications, hybrid approaches are a viable alternative. In this paper, an interactive RANSE/BEM methodology is presented, where the propeller is replaced by rotating body forces that map the actual loading state of the blades, allowing a fully unsteady analysis of hull–propeller interaction. The methodology is applied to the straight ahead and 8.4° pure drift motions of a twin screw propulsive configuration. Last, but not least, the study presents a validation study with accurate experimental data of the nominal wake field and single blade loads.
Highlights
Propeller performance is strongly influenced by the working conditions during the manoeuvres
The interactive procedure steps dedicated to the velocity prediction by RANS, the correction of the boundary element method (BEM) boundary conditions from the effective inflow, the BEM prediction of the blade pressure distribution and the body–force distribution in the torus block are sketched in Figure 1
Results of the un-propelled hull are shown in terms of velocity field at the transverse plane in the propeller region, starboard side, by PIV measurements and hybrid RANS/BEM predictions (Figures 4–6), in case of straight-ahead motion
Summary
Propeller performance is strongly influenced by the working conditions during the manoeuvres. Since the blades have to be represented the body forces are usually predicted by BEM models in the context of ship propulsion [14,15,16,17], the simpler BEMT models, enhanced with a priori corrections obtained by viscous flow computations, can be a computationally cheaper alternative [18] In this regard, a preliminary validation study showed that BEMT and BEM provided comparable results for the same test case studied in [2] in terms of maneuvering loads [19]. The local phenomena are analyzed with the support of the pressure distribution on key sections over the blade revolution
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