Unsteady analysis of six-DOF motion of a 6:1 prolate spheroid in viscous fluid

Free-moving simulations of airplanes, submarines and other automobiles under extreme and emergency conditions are becoming increasingly important from operational and tactical perspectives. Such simulations are fairly challenging due to the extreme unsteady motions and high Re (Reynolds) numbers. The aim of this study is to perform a six-DOF motion simulation of a 6:1 prolate spheroid that is falling in a fluid field. Prior to conducting the six-DOF simulation, some verification simulations were performed. First, a laminar flow past an inclined prolate spheroid at a Re number of 1000 and incidence angle of 45° with a tetrahedral mesh was simulated to verify the relevant targeted discrete method for an unstructured mesh. Second, to verify the LES (large eddy simulation) models and dependent parameters for the DDES (delayed detached eddy simulation), a turbulent flow past a sphere was performed at a subcritical Re number of 10000. Third, a steady maneuvering problem about a prolate spheroid pitching up from 0° to 30° incidence at a uniform angular velocity was established based on a dynamic tetrahedral mesh with changing topology and the ALE (arbitrary Lagrangian-Eulerian) method of fluid-structure coupling at a Re number of 4.2 × 10⁶. Finally, two six-DOF motions of an inclined 6:1 prolate spheroid at an initial incidence of 45° were simulated at different Re numbers of 10000 and 4.2 × 10⁶.