Analysis of the influence of an upstream rudder over the wake features of a submarine propeller

Large-Eddy Simulation is utilized to analyze the effect of an upstream rudder on the wake features of a submarine propeller. Three incidence conditions of the rudder, relative to the free-stream, are considered. Results are also compared with the solution generated in open-water conditions. The overall approach on the same propeller was validated by an earlier study on the open-water configuration and the same advance coefficient, via comparisons with Particle Image Velocimetry experiments of the wake flow and dynamometric measurements on the parameters of global performance. Results reported in this work demonstrate that the disturbance at the inflow of the propeller does not change substantially the topology of the largest coherent structures within the near wake (the tip and hub vortices). In addition, as long as the flow over the rudder keeps attached, the levels of fluctuations downstream of the propeller are only slightly increased and thus the perturbation of the inflow keeps small. However, at the largest simulated incidence condition the separation occurring over the suction side of the hydrofoil causes instead more substantial changes on wake turbulence, although also in that case the near wake coherence of tip and hub vortices is almost unchanged. At the same condition, downstream of the instability of the wake system, the interaction with the structures shed from the ends of the hydrofoil further increases the unsteady nature of the wake flow and the extent of the flow region affected by large values of turbulent fluctuations.