A dynamic study of the high-speed oblique water entry of a stepped cylindrical-cone projectile

Abstract

High-speed oblique water entry is an interesting subject, many physical aspects of which remain unknown up to now. Among high-speed air-to-water projectiles, the supercavitating cylindrical-cone (SCC) ones have economic and operational advantages over the other types. However, maintaining stability of the SCC projectiles inside the cavity at shallow entry angles is a challenging issue from both practical and design-related points. The first section of the present study proposes a novel and unique scheme of air-to-water supercavitating projectile design which is called the supercavitating stepped cylindrical-cone (SSCC) projectile. The SSCC scheme is analyzed numerically to investigate the projectile stability improvement at shallow entry angles. The 6DOF dynamics of the SSCC projectile are investigated using the Star-CCM+ commercial code in the presence of three phases of air, water and vapor in a three-dimensional and transient model. Accuracy of numerical results and the model's ability to simulate the physical phenomena of water entry is validated using experimental results from the literature, and both are in good agreement. In the present study, the high-speed oblique water entry dynamics of the SSCC projectile are investigated for five certain entry angles varying from 10° to 60°. The results show that the SSCC projectile faces intensive unstabilizing forces in the water entry process which leads to a heavy pitching moment and, hence, intensive angular velocity (̇) on the projectile. This study also proves that the presence of step enhances the projectile stability in the entry process. The present study shows that, based on their geometry and mass characteristics, each SSCC projectile is capable of withstanding instability up to a critical value of the angular velocity (̇C r). Therefore, projectile stability inside the cavity can be achieved when the value of maximum angular velocity (|̇| max) experienced by the projectile is lower that ̇C r (i.e., |̇| max <̇C r). The results of this study also show that |̇| max is inversely correlated with the , and that it follows a simple equation which is proposed in this study. Therefore, projectile stability inside the cavity can also be practically achieved by adjusting the shooting mechanism at an angle higher than the minimum stable entry angle (min). This study also proposes an effective numerical approach to evaluate min of a supercavitating projectile. It should be noted that determining the value of min is an important factor from both a practical and design-related points of view.

Experimental Investigation into the Tail-Slapping Motion of a Projectile with an Oblique Water-Entry Speed

“…Zhao et al [29] studied the tail-slapping law of underwater projectiles with a speed of less than 50 m/s by MATLAB simulation. In addition, by means of computer numerical simulation technology, Akbari et al [30] adopted the numerical simulation method to study the process of oblique water-entry of the stepped head projectile, and briefly described the tail-slapping phenomenon, which mainly analyzed the motion law of the projectile. The next year, they (Akbari et al, [31]) conducted studies on the projectile motion characteristics of water entry under different length-diameter ratios and established the connection between the length-diameter ratio of the projectile and the motion stability.…”

“…In addition, by means of computer numerical simulation technology, Akbari et al [30] adopted the numerical simulation method to study the process of oblique water-entry of the stepped head projectile, and briefly described the tail-slapping phenomenon, which mainly analyzed the motion law of the projectile. The next year, they (Akbari et al, [31]) conducted studies on the projectile motion characteristics of water entry under different length-diameter ratios and established the connection between the length-diameter ratio of the projectile and the motion stability. Gu et al [32] obtained the weight parameters of the supercavitating projectile and summarized the influence of the weight parameters on the motion characteristics of the tail-slapping.…”

Motion Characteristics of High-Speed Supercavitating Projectiles Including Structural Deformation

“…Ishchenko et al [8] shot supercavitating projectiles into water at an initial speed of nearly 1000 m/s, and analyzed the structural deformation phenomenon caused by the huge hydrodynamic force. Akbari et al [9] studied the hydrodynamic characteristics of supercavitating projectiles launched obliquely into water, and found that the supercavitating projectiles were subjected to a significant normal impact force which was closely related to the wet area. The experimental results of Chen et al [10] showed that supercavitating projectiles could fly stably in a tail-slap mode, indicating that an approximately periodic hydrodynamic force acts on the supercavitating projectile during the underwater motion process.…”

Study on the Influence of Temperature on the Temporal and Spatial Distribution Characteristics of Natural Cavitating Flow around a Vehicle

“…To date, many experimental and numerical studies have investigated the flow characteristics of cavitation [7][8][9][10]. Knapp [11] observed and analyzed cloud cavitation flow and pointed out that the re-entrant flow from the closed cavity position is the cause of cloud cavitation ruptures.…”