Large-eddy simulations for the case of an axisymmetric body of revolution with appendages are considered. The geometry is the benchmark case of the DARPA suboff body. The paper focuses on the effects of the Reynolds number on the structure of the boundary layer in the stern area as well as the near wake. For this purpose we compare results for two Reynolds numbers (based on the length of the body, . An azimuthal readjustment of turbulent kinetic energy occurs in the wake, becoming more axisymmetric, with increasing values in the planes aligned with the stern appendages, due to turbulence coming from both the stern boundary layer and junction vortices.

The acoustic analogy is adopted to characterise the signature of a seven-bladed submarine propeller, relying on a high-fidelity large-eddy simulation, performed on a computational grid consisting of 840 million points. Results demonstrate that the nonlinear terms of the Ffowcs-Williams and Hawkings equation quickly become dominant moving away from the propeller along the direction of its wake development. While the linear terms experience a decay moving downstream, the nonlinear terms grow in the near wake, as a result of the development of wake instability. In particular, this growth affects frequencies lower than the blade frequency. Therefore, the acoustic signature of the propeller is mainly tonal in the near field only, due to the thickness and loading components of noise from the surface of the propeller and the periodic perturbation caused by its tip vortices. They develop instability at a faster rate, compared with the hub vortex, triggering the process of energy cascade towards higher frequencies and contributing in this way to broadband noise.

Large-eddy simulation is utilized to reproduce the instability of the tip vortices shed from the blades of an axial-flow turbine. The oscillations of their helical trajectories trigger mutual interaction between them. This accelerates the process of their destabilization, leading to leapfrogging and eventually to breakdown into smaller structures and loss of coherence, initiating wake contraction and momentum recovery from the outer radii towards the wake core. A strong correlation of the tip vortices instability with the behaviour of the Reynolds stresses and turbulence production is observed. In particular, the turbulent shear stress tied to the fluctuations of the radial and axial velocity components reveals the significant role of the interaction of each tip vortex with the outer region of the wake of the preceding blade, creating a ‘bridge’ between neighbouring tip vortices. Such an interaction enhances the process of mutual inductance between them, promoting production of turbulence and destabilization of the coherent structures. The latter results in increasing oscillations of the radial location of their cores and in a significant jump of the normal turbulent stress of radial velocity within them. Further downstream, the instability of the tip vortices triggers intense mixing phenomena between the outer free stream and the inner wake flow, leading the process of momentum recovery and wake contraction.

Large eddy simulations are presented on the wake flow of a notional propeller (the INSEAN E1658), upstream of a NACA0020 hydrofoil of infinite spanwise extent, mimicking propeller–rudder interaction. Results show that the flow physics is dominated by the interaction between the coherent structures populating the wake of the propeller and the surface of the hydrofoil. The suction and pressure side branches of the tip vortices move towards inner and outer radii, respectively. The hub vortex is split into two branches at the leading edge of the hydrofoil. The two branches of the hub vortex shift in the opposite direction, compared to the tip vortices, towards the rudder suction sides. As a result, a contraction of the propeller wake on the suction sides occurs, leading to increased levels of shear stress and turbulence. At downstream locations along the hydrofoil the spanwise deflection of the suction side branches of the tip vortices affects the trajectory of the overall propeller wake, including also the smaller helical vortices across the span of the wake of each blade and the two branches of the hub vortex on the two sides of the hydrofoil. This cross-stream shift persists, producing a strong anti-symmetry of the overall wake.