Numerical investigation on the tail slamming for the high-speed oblique water entry of the slender cylinder

During high-speed oblique water entry, the slender vehicle is subjected to intense impact loads, particularly the normal loads induced by tail slamming. These loads significantly compromise attitude stability and structural integrity. However, the underlying mechanisms of tail slamming dynamics in such configurations have not been fully elucidated. This study conducts a numerical analysis of the oblique water entry of a slender cylinder, focusing on the tail slamming formation mechanisms and the influence of initial motion conditions. A numerical model using on an improved immersed boundary method is established and validated against experimental oblique water-entry data to ensure reliability and accuracy. The results reveal that the pitching moment generated during cylinder crossing the water surface is the primary driver of the pitching motion responsible for the tail slamming. The pressure distribution along the wet area on the cylinder head varies with the water-entry angle, critically influencing the formation characteristics of the pitching moment. As the water-entry angle increases, the evolution curve of pitching moment transitions from a single peak to a positive-negative double peak, and the cavity diameter decreases progressively. The timing and maximum normal impact force of tail slamming exhibit a non-monotonic relationship with the water-entry angle but scale linearly with the water-entry velocity. Furthermore, the dimensionless coefficients of the pitching moment exhibit overlap across different water-entry velocities early in the water-entry process. This work provides novel insight for mitigating tail-slamming loads during high-speed oblique water entry of slender underwater vehicles.