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Comparison the cavity sizes with various grid densities.

Comparison the cavity sizes with various grid densities.

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Tail slapping is considered to be a prominent mode for facilitating the movement of supercavitating projectiles underwater. Stability mechanism of the tail slapping and stability criterion of projectiles was numerically investigated in this paper. A numerical method was conducted to calculate the free flight of projectiles by combining the finite v...

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... Unlike high-velocity projectile experiments, water tunnel experiments provide detailed insights into cavitation at lower velocities, which are convenient for studying cavitation mechanisms. 18 Foeth et al. 19 investigated the three-dimensional (3D) hydrofoil sheet cavitation in a water tunnel by employing the time-resolved particle image velocity measurement (PIV) method, confirming the significant influence of the 3D geometry of the hydrofoil on the flow dynamics and stability of the cavitation pattern. Since the equipment severely limited the flow velocity in experimental water tunnels, it was challenging to achieve natural supercavitation. ...
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The effects of rotational motion around the central axis of a supercavitating underwater cylindrical vehicle are numerically investigated with the cavitation process at a cavitation number of 0.0198. The relationships among tangential velocity, streamwise vorticity, flow field pressure distribution of the flow field, mass transfer rates of water and water vapor, and cavity shapes are analyzed under varying rotational speeds. Compared to non-rotational motion, the distinct cavitation mechanisms in rotational motion are identified. The results indicated that during the initial cavitation stage, the tangential velocity near the vehicle's surface rises as the rotational speed increases, gradually decreasing the pressure and transforming water into water vapor. Simultaneously, the concave structure at the end of the front cavity near the vehicle's surface progressively disappears. This accelerates the cavitation process, causing the earlier merger of the front and rear cavities. Following this process, a concave structure appears at the center of the cavity tail for the non-rotating vehicle due to the pressure increase. However, this concave structure gradually transforms to a convex structure with increasing rotational speed. This phenomenon is attributed to the tangential velocity generated by the vehicle's rotation, which causes the pressure in the rear cavity to rise very slowly, and the low-pressure region contracts toward the axis line. The mass transfer in the rear cavity of the rotating vehicle is significantly improved with pressure changes, transforming from vapor into water. Therefore, the pressure changes and mass transfer rate induced by rotation lead to converting the rear cavity end from a concave to a convex structure.
... Treichler and Kiger (2020) recorded cavitation images and the pressure near the cavity when a supercavitating projectile entered water and found that cavity dynamics were closely related to the size of the tank. Liu et al. (2024) conducted underwater high-speed launch tests of supercavitating projectiles (SCPs) and studied the stability mechanism of tail slapping and the stability criteria for SCPs. ...
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In this paper, high-speed photography was employed to experimentally study the high-speed, shallow-angle water entry of cylinders. By varying the density, length–diameter ratio, and launch speed of the cylinders, three typical trajectories were observed: arc, S, and ricochet trajectories. This study examined the cavity evolution, motion trajectory, force state, and stability of the cylinders under these three typical trajectories. Additionally, the influence of each cylinder's length–diameter ratio and density on the stability of its motion during shallow-angle water entry was explored. The experimental results indicated that during the impact stage, the cylinder generates a head-down torque, resulting in an upward deflection after entry. The combination of head force and angle of attack generates lift, which increases with a positive angle of attack. Consequently, the cylinder's deflection speed accelerates, while it slows with a negative angle of attack. During the tail-slap process, the combined forces from the head and tail both generate lift, but in the opposite directions. The motion stability decreases sequentially in the arc, S, and ricochet trajectories, which is closely related to the first tail-slap. Increasing the cylinder length–diameter ratio or density delays the occurrence of the first tail-slap, thereby enhancing motion stability during shallow-angle water entry.
... In contrast to natural supercavities, ventilated supercavities can be formed at relatively low vehicle speeds. 7,8 Furthermore, the geometry of a ventilated supercavity is controlled by regulating the ventilation rate. 9 When the effect of gravity on supercavity deformation is neglected, a supercavity maintains symmetry, and its closure mode manifests as a reentrant jet. ...
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