Mechanisms of spike-induced cavity dynamics and drag reduction in submerged high-speed flows

High-speed underwater vehicles experience significant hydrodynamic drag, which limits their performance and operational efficiency. Spike devices have been proposed as an effective drag-reduction technique by inducing cavity formation in front of the vehicle. This present study focuses on the drag reduction mechanism induced by a spike under fully submerged high-speed conditions. Using the three-dimensional Reynolds-averaged Navier–Stokes approach based on the interPhaseChangeFoam solver in OpenFOAM®, high-speed underwater numerical simulations are conducted to systematically investigate the effects of flow parameters and structural parameters on the flowfield characteristics and force acting on the vehicle. The results reveal that the vehicle's drag is strongly dependent on the aerodisk diameter (d), inflow velocity (v), and angle of attack (α), whereas the length-to-diameter ratio (L/D) has a comparatively minor effect. An optimal d exists, namely an excessively small d fails to achieve a stable cavity, while an excessively large d causes the drag force on the spike to increase sharply. For the hemispherical aerodisk, critical values of d and L/D exist for the occurrence of cavitation instability. In contrast, the flat-faced aerodisk can generate a stable cavity at a smaller d and exhibit weak sensitivity to L/D. Higher v promote the cavity to fully wrap the vehicle. Increasing the α disrupts flowfield symmetry, leading to a rapid drag increase beyond 6°. Selecting an appropriate d, controlling the α, and optimizing L/D are therefore key strategies to enhance drag-reduction performance of trans-media vehicles.