Shape, Development and Stability of a Supercavitation Bubble
The Supercavitation phenomenon has been studied for decades utilizing the nature vaporization of the water surrounding high speed underwater vehicles to reduce the drag acting on the supercavitational bodies. Yet, many questions and problems remained open and unsolved regarding the process and the characteristics of the bubble and the supercavitational regime. Understanding the creation and development, the shape, and the stability of a supercavitation bubble is essential for the design of supercavitational underwater vehicles and applications and it is at the center of this study.
To enhance understanding of the supercavitation bubble shape and structure, two series of experiments have been conducted in two advanced systems: one resemble a duct flow, and the other a free-surface flow. The experiments have been applied on cylindrical slender bodies in a uniform flow of water, in different flow speeds. A comparison of supercavitation bubbles created on bodies with different nose geometries (i.e., cavitators), has been made. The comparison was referred to the conditions of the bubbles’ creation and collapse, and also their shape and development.
Also theoretical efforts have been made, in order to examine the supercavitation bubble geometry. An analytical model of an axisymmetric supercavitation bubble in a viscous flow has been made. The viscosity of the flow has typically been neglected in research on supercavitational flows, using non-viscous potential flows. However, for some situations and conditions, the viscosity was found to be significant and crucial for the bubble geometry and formation, especially at the supercavitation bubble detachment point. The results of the analyses show the change of the bubble formation from past models due to the viscosity, and offer a more accurate description of the bubble geometry.
Another theoretical examination conducted in this study, aimed at learning about the pressure field of the supercavitation bubble. Actually, the underwater vessel is surrounded by an inhomogeneous fluid containing cavities (also described as microbubbles). The distribution of the cavities in the supercavitation volume dictates the pressure field and thus determines the stresses and forces that act on the vessel and affect its motion and stability. In this research, we suggest a new approach to studying the bubbles’ formation and learning about the cavities’ distribution in the low-pressure volume using a stochastic model, describing the random movement of the cavities.
