Cavity dynamics of water entry for spheres and ballistic projectiles

[摘要] (cont.) This thesis examines the effect of several key parameters on the water entry physics of spheres at relatively low Froude numbers including: hydrophobic vs. hydrophilic surfaces, mass ratio and rotational velocity. Physical models that predict the depth of deep seal and the effect of dynamic and static wetting angle on cavity formation will be discussed. Theories are derived from physical parameters witnessed through high-speed video image sequences using advanced image processing techniques. New phenomena have been witnessed via these techniques including a wedge of fluid that crosses the cavity in the case of transverse rotational velocity. Furthermore, the images reveal the forces acting on the sphere through the entire trajectory, which adds valuable information for future theoretical models. The discussion continues with the water entry of bullets, which produce water vapor cavities large enough to engulf the projectile (i.e. supercavitation). The effects of speed, geometry and angle of attack on the formation of the subsurface cavity are analyzed through an improved physical model and full scale experimentation. The analytical model is then used to improve the design of projectile geometry to allow for more efficient travel inside the cavity and experimentally validated.

[发布机构] Massachusetts Institute of Technology