LES study of the wake features of a propeller in presence of an upstream rudder

Large-Eddy Simulations were carried out on a notional submarine propeller in presence of a disturbance at the inflow, associated to the wake of an upstream hydrofoil, mimicking a rudder. Three orientations of the hydrofoil were simulated, equivalent to angles of incidence of alpha = 0 degrees, alpha = 10 degrees and alpha = 20 degrees, respectively. Results were also compared with the open-water configuration, featuring the same propeller in isolated conditions. Present computations demonstrate that the topology of the largest coherent structures, that are the tip vortices and the hub vortex, is practically unchanged across the three cases with different inflow perturbations. In the near wake, for alpha = 0 degrees and alpha = 10 degrees turbulent fluctuations within the propeller wake were increased only locally, at the azimuthal positions corresponding to the wake of the hydrofoil. In contrast, for alpha = 20 degrees. featuring separation over the suction side of the hydrofoil and thus a wider disturbance at the propeller inflow, turbulence within the core of the tip vortices was affected also at azimuthal positions away from the ingested perturbation. For the same condition also the wake axis demonstrated a stronger destabilization of the hub vortex, compared to the cases with milder disturbances, with about a four fold increase of turbulent kinetic energy, relative to the open-water condition. Downstream of the destabilization of the wake system, increasing values of turbulent kinetic energy were associated to growing incidence angles of the upstream hydrofoil. (C) 2019 Elsevier Ltd. All rights reserved.