Analysis of vortices shed by a notional submarine model in steady drift and pitch advancement

Results of Reynolds-averaged Navier-Stokes simulations are reported on a towed fully-appended notional submarine model. Computations are validated against data in the literature, dealing with both global loads and the vortices originating from the sail. The analysis of the flow is focused on the coherent structures shed from the tip and the root of the appendages, defining the wake signature of the submarine and affecting the flow field over the propeller plane. Their positions and intensities are compared across four operative conditions: straight ahead, drift, and both positive and negative pitch. Computations demonstrate that the condition with negative pitch is the one producing the most complex topology of the flow in the stern region, where the vortices from the tip of the sailplanes are able to influence both the fins and the flow at the propeller plane. However, the widest and most intense vortex is generated in drift, from the tip of the sail, because of the strong gradient of pressure produced between the two sides of the fore appendages. The pattern of the coherent structures produced by the stern appendages is substantially dependent on the maneuvering conditions. In both pitch conditions their tip vortices have values of circulation very similar across the four fins. This is not the case in drift: the one most affected by the wake of the sail is the smallest and weakest. The most intense junction vortices from the stern appendages, which are able to influence more directly the inflow of the propeller, occur instead in drift.