Scale Effect on the Hydrodynamic Performance of a Ducted Propeller under Consideration of Flow Transition and Cavitation

Abstract

The paper presents a numerical investigation of the scale / Reynolds number effects on the hydrodynamic performance of a 4-bladed ducted propeller under open water test conditions. In the numerical simulations, the influences of flow transition and cavitation are taken into account. The RANS calculations are carried out using the ANSYS-CFX solver. For turbulence modelling, the Explicit Algebraic Reynolds Stress Model (EARSM) is applied in combination with the γ-Re θ transition model. The cavitation model employed is based on the Rayleigh-Plesset equation. In order to evaluate the various Reynolds number effects separately, different geometrical configurations are investigated. The first configuration is a 2D NACA66Amod hydrofoil. In this case, the investigation focuses on the laminar-turbulent flow-transition behaviour on the surface of the hydrofoil. In order to be able to study this behaviour on 3D geometries, a simplified blade geometry based on the hydrofoil mentioned above is developed and integrated in a neutral free-slip duct, which produces zero thrust. This configuration allows for investigating the flow transition at different regions of the rotating blade. Additionally, the flow on the Wageningen 19A duct is simulated in order to evaluate the scale effect on the hydrodynamic performance of the duct without considering scale influence induced by the propeller. In this case, the propeller flow is simulated using an actuator disc model. The final geometrical configuration is a ducted propeller that consists of a 4-bladed propeller in combination with the Wageningen 19A duct. The investigation of this configuration focuses on the change of the flow behaviour and the hydrodynamic characteristics over a wide range of Reynolds numbers. The influence of the Reynolds number on the thrust-torque ratio of the ducted propellers, particularly on the thrust breakdown behaviour at three propeller loads, is evaluated.