Propeller-Hull Interaction Effects in Calm Water and Regular Head Waves

Doctoral thesis, 2024

In order to design fuel-efficient ships and install compatible propulsion systems, ship and propeller designers need to know the potential effects of the interactions between different ship components, e.g., hull, propeller, appendages and machinery, on the ship performance at sea. Neglecting the interaction effects may result in unbalanced powering which adversely affects the energy/fuel consumption, hence increasing ships operational cost and environmental impact. Developing accurate and reliable engineering methods that can predict the ships required power considering the interaction effects, can be an important contribution to achieve the aforementioned needs of the shipping industry.

Traditionally, power prediction has been carried out for ships operating in calm water rather than more realistic environmental conditions. However, waves can play a crucial role on the ship performance at sea. The interactions between waves, hull and the propulsion system of a ship may significantly affect the ship motions, resistance, wake, speed and propeller/engine load in comparison to calm water operational conditions. Nonetheless, it is practically impossible to take all of the entailed interactions between different ship components into consideration within the process of power prediction in all possible operational and environmental conditions, hence a series of assumptions and simplifications are often introduced.

In this thesis, as a step towards the ship power prediction in more realistic environmental conditions, the propeller-hull interaction effects in a range of selective operational conditions in calm water and regular head waves are considered in model-scale. The main objective is to perform numerical investigations of the ship performance in these conditions, aiming at understanding the involved flow physics in the propeller-hull interaction effects on the ship behavior and its propulsion characteristics. The investigations in both calm water and regular head waves are carried out in three distinctive steps: only the bare hull consideration, only the propeller consideration known as propeller open water (POW) and finally, for the self-propelled hull. The bare hull investigations incorporate employing two computational methods: a Fully Nonlinear Potential Flow (FNPF) panel method and a state-of-the-art Computational Fluid Dynamics (CFD) method using a Reynolds-Averaged Navier-Stokes (RANS) approach. However, for the POW and self-propulsion studies only the RANS approach is employed. A formal verification and validation (V&V) procedure is applied to understand and control the numerical and modeling errors in the RANS computations.

Overall, the results of the employed numerical methods were in good agreement with the experimental data. The analysis of the results provided valuable insight into the ship and propeller hydrodynamic performance in terms of the ship motions, resistance, wake, propeller characteristics and the correlations between them. The ship hydrodynamics analyses from this thesis can shed more light onto the propeller-hull interaction effects in waves and help the ship/propeller designers optimize their designs for more realistic conditions than only calm water.