When a submarine executes a turn in the horizontal plane, it experiences a pitching moment due to out-of-plane forces that push the stern downwards, giving an upward pitching moment. This study uses Computational Fluid Dynamics (CFD) to examine the distribution of the downward force over the stern.

Three different configurations of the generic Joubert submarine, which represents a contemporary conventional submarine, in a steady turn were examined. The three configurations were the: bare hull; hull and casing; and finally hull, casing and sail. The magnitude and location of the out-of-plane forces were obtained in each case.

Results show that both the sail and casing generate out-of-plane forces on the stern of the submarine when in a steady turn, although their effects on the submarine are different. The primary cause of the downward force over the stern is the presence of the sail. This is discussed in the paper with due regard to the hydrodynamic effects of the sail vortices on the flow around the submarine hull.

The developed CFD model will be used for further investigation of the out-of-plane forces and the phenomenon’s dependence on the submarine turning angle, turning rate, and the shape and location of the submarine hull and sail. Understanding the phenomenon will contribute to further research and development into the hydrodynamics of submarines, both in the design and operational phases.