Water entry of spheres with impact-axis channels

This paper comprehensively investigates the non-axisymmetric cavity dynamics of a vertically entering sphere under the influence of nearby side-walls through experimental, numerical, and theoretical analyses. Initially, we explore the characteristics of cavity evolutions with the sidewall effect. The emergence of a twin-vortex during cavity pinch-off is observed, and detailed numerical simulations provide insights into its underlying mechanisms. Both the dimensionless distance (λ) and the Froude number Fr significantly influence the pinch-off type. A phase diagram in the λ−Fr parameter space is presented, revealing the interplay between these variables. Moreover, we investigate the sidewall effect on the pinch-off time and location at low Froude numbers. The findings indicate that as λ decreases, both the pinch-off time and depth of the cavity increase. Generally, the wall effect is relatively weak when λ exceeds 4. Additionally, the pinch-off time can be described by τ=kr/g, with the constant k determined by λ. Utilizing 2D cavity theory, we estimate the pinch-off time of the water entry cavity with the sidewall effect, revealing a consistent collapse behavior with the mechanics of a two-dimensional cavity.

The effect of a side wall on cavity dynamics during the water entry of a sphere at low Froude numbers

Sui,

Han,

Wang

et al. 2024

Experimental and numerical study on cavity dynamics during near-water-surface skipping motion of a non-spinning disk

Li,

Wang,

et al. 2024

In this paper, we present a comprehensive set of experimental and numerical studies on the near-water-surface skipping motion of three-dimensional, non-spinning disks. Qualitative analyses were conducted on the experimental results to examine the effects of inclination angle on cavity evolution. Additionally, numerical results are utilized to study the impact of the attack angle on hydrodynamic forces and motion characteristics of the disk. Key findings of this study include the following: (1) an asymmetric cavity will be formed during the near-water-surface skipping motion of the disk; (2) two distinct cavity shapes, U-shaped and W-shaped, emerge under varying initial inclination angles; (3) decreasing the inclination angle reduces the angle between the splash and the water surface, improving the possibility of a successful skipping motion; (4) disks with excessively large positive or negative inclination angles tend to dive into the water; (5) an instantaneous significant reduction in inclination angle during impact results in dual peaks of vertical force, with corresponding increases in hydrodynamic forces and pitching moments as the impact angle increases; and (6) disks with extremely small impact angles are prone to overturning and diving into the water.

Water entry of a seaplane section considering the wave effect

Sun,

Zhang

et al. 2024

The landing of a seaplane on the wave is a crucial issue with practical engineering applications in the fields of aeronautical and ocean engineering. The safe landing of seaplanes on wave surfaces prompts an urgent investigation on further understanding the mechanism by which the wings affect loads. This study examines the slamming force characteristics, pressure distributions, and free surface profiles of a two-dimensional seaplane section with varied heel angles into waves, considering different entry velocities, entry locations, and wave steepnesses. The overset mesh technique has been integrated into the waves2Foam toolbox to achieve a numerical wave tank based on the overset mesh. Numerical results for the vertical slamming force, slamming pressure coefficient distribution, and free surface profile were validated against published semi-analytical solutions and laboratory tests. The slamming force during the water entry of the seaplane section under the wave effect shows similar but more complex characteristics than those of the wedge section, manifesting as a phenomenon of multiple peaks. In addition to the bottom slamming of the airframe, localized high-pressure regions appear beneath the wing due to the combined squeezing effect on the air layer by the wing and water particle, which is similar to the wing-in-ground (WIG) effect. Slight sawtooth fluctuations of the wavefront were observed as a consequence of the disturbance of the air layer by the wings.