Experimental and Numerical Investigation of Propeller Loads in Off-Design Conditions

Abstract

The understanding of the performance of a propeller in realistic operative conditions is nowadays a key issue for improving design techniques, guaranteeing safety and continuity of operation at sea, and reducing maintenance costs. In this paper, a summary of the recent research carried out at CNR-INSEAN devoted to the analysis of propeller loads in realistic operative scenarios, with particular emphasis on the in-plane loads, is presented. In particular, the experimental results carried out on a free running maneuvering model equipped with a novel force transducer are discussed and supported by CFD (Computational Fluid Dynamics) analysis and the use of a simplified propeller model, based on Blade Element Momentum Theory, with the aim of achieving a deeper understanding of the mechanisms that govern the functioning of the propeller in off-design. Moreover, the analysis includes the scaling factors that can be used to obtain a prediction from model measurements, the propeller radial force being the primary cause of failures of the shaft bearings. In particular, the analysis highlighted that cavitation at full scale can cause the increment of in-plane loads by about 20% with respect to a non-cavitating case, that that in-plane loads could be more sensitive to cavitation than thrust and torque, and that Reynolds number effect is negligible. For the analysis of cavitation, an alternative version of the BEMT solver, improved with cavitation linear theory, was developed.

Numerical Prediction of Cavitation Fatigue Life and Hydrodynamic Performance of Marine Propellers

“…As a propeller operates underwater, it experiences periodic bubble generation and collapse on its blades, resulting in impact loads on the blade surface [10]. The rotation process of the propeller generates periodic unsteady dynamic loads on the blade surface [11], causing significant variations in surface load distribution in different media such as gas and liquid. Additionally, at higher propeller speeds, the frequency of alternating changes in blade stress becomes too rapid.…”

Experimental investigation on the effect of Leading Edge Tubercles on the Performance of Marine Propellers in fully wet condition

“…During maneuvers or motion in waves, the blades, optimized for the inflow in ideal condition (straight ahead advancement in calm water), are subjected to a different angle of attack. As a consequence, the mean loads and their fluctuation as well as the onset, development and features of the cavitation pattern can be altered (Ortolani and Dubbioso, 2019b,a), affecting the structural reliability of the propulsive components (Ortolani et al, 2018; or emitted noise . Moreover, unmanned autonomous vehicles are rapidly expanding for various mission profile at sea (as well as land and air).…”

Multi-Degree of Freedom Propeller Force Models Based on a Neural Network and Regression

“…Common ways of modeling a discretized propeller are with the overset method or sliding mesh methods [1][2][3][4]. The cost can be prohibitive for CFD of a maneuvering vessel, especially in waves and at full scale [5]. Maintaining the accuracy of a viscous CFD method while decreasing the computational cost is desirable.…”

“…The body force can be applied to the flow and to the vessel equations of motion. This approach can be used with a constant body force [6], a database driven model [7], Boundary Element Models [8], semi-empirical methods [9,10], or by using Blade Element Momentum Theory [5,[11][12][13]. Methods that ignore viscous effects may not be as accurate as modeling a fully discretized propeller with CFD in off design conditions.…”