Impact response of flowing-fluid filled square vessels

The concept of cavitation drag reduction is widely known in many fields. However, the existence of cavitation is not beneficial to the protection of structures. In this study, an attempt was made to improve the protection efficiency of fluid-filled vessels by adopting the reverse approach of increasing drag forces by reducing cavitation: The vessels were filled with flowing fluids to reduce the pressure and change the shape of cavitation during penetration. Ballistic tests, numerical simulations, and theoretical analyses were conducted to evaluate the impact response of flowing-water filled square vessels impacted by a spherical projectile. The impact responses of flowing-water filled square vessels were analyzed and compared with static-water filled vessels, in terms of the deformation and failure of target panels as the vessel's walls, sidewall pressure time histories, and cavitation processes. Moreover, the mechanism of increasing drag forces due to the fluid flow was elucidated. The effects of fluid flow on the cavitation and pressure distribution were determined. This study elucidated the active attenuation mechanism of fluid flow on mitigating the damage of rear panel. The results show that fluid flow can increase the drag forces, leading to a higher protection efficiency of flowing-water filled vessels than static-water filled vessels. Owing to the effect of fluid flow, sidewall pressures are evidently lower than those in static fluid cases. Fluid flow can change pressure distributions in the vicinity of cavitation, which can alter not only the cavitation shape but also the action direction of cavitation jetting. The active attenuation effect of fluid flow predominantly contributes to mitigating the pressure accumulation on the inner surface of rear panel during penetration, resulting in lower pressures and subsequently less damage to the structures. This study sheds light on the benefits of flowing-fluid filling on increasing the drag forces as well as mitigating the cavitation pressures.