The paper “End effects in the wake of a hydrofoil working downstream of a propeller”, authored by Dr. Antonio Posa from CNR-INM, was selected in the Editor’s picks by the editorial board of Physics of Fluids and published on the home page of the journal.
Large Eddy Simulation was utilized to reproduce the flow physics of a system composed of a propeller working upstream of a hydrofoil, mimicking a rudder. A computational grid consisting of 3.8 billion points was adopted. Computations were carried out across a range of incidence angles of the hydrofoil and were compared against the results of an earlier study, dealing with a similar hydrofoil of infinite spanwise extent, with the purpose of shedding light onto the influence of the end effects on the flow physics.
The simulations demonstrated almost no changes between the two hydrofoil geometries at conditions of zero incidence. This was increasingly not the case for growing incidence angles. They resulted in the onset of large streamwise-oriented vortices from the tip of the hydrofoil. Meanwhile, the flow physics was complicated by the roll-up of the vortices shed from the tip of the propeller blades around those shed by the hydrofoil, where the highest turbulent stresses were produced. However, the momentum shifting from the pressure side towards the suction side of the hydrofoil through its bottom end prevented the onset of the massive separation phenomena observed on the suction side of the hydrofoil of infinite spanwise extent.
The results of this work highlight that the infinite approximation of the hydrofoil geometry, often adopted in studies dealing with the interaction of the propeller wake with downstream rudders, is accurate enough at conditions of no incidence. In contrast, it can lead to large errors for angles large enough to trigger separation on the suction side of the rudder.
More details can be found at:
https://doi.org/10.1063/5.0146297
https://doi.org/10.1063/5.0131624