Large-Eddy Simulations of a notional submarine in towed and self-propelled configurations

The present study reports results of Large Eddy Simulations (LES) in towed and self-propelled conditions for the DARPA SUBOFF (DSub), a notional submarine geometry, at a Reynolds number, based on the model length, L, and the free-stream velocity, U∞, equal to ReL=1.2×106. An Immersed-Boundary (IB) method was adopted to enforce no-slip boundary conditions on the surface of the body. The approach (LES with IB) was validated by the authors in earlier studies on the towed DSub, as well as on the INSEAN E1619 propeller in open-water conditions. Comparisons between towed and propelled configurations are presented here. Results show that the development of the boundary layer over the cylindrical mid-body is almost unaffected by propeller suction. Instead, the effect over the stern is dramatic, modifying substantially the flow ingested by the same propeller. In the wake the bimodal distribution of the turbulent stresses for the towed case, due to the adverse pressure gradient induced by the tapered geometry of the stern, is replaced in self-propulsion by an axial peak of turbulent kinetic energy, mainly due to instability of the hub vortex.