Relationship between a non-spherical collapse of a bubble and a stress state inside a wall

Abstract

This study performed a fluid/material coupled numerical simulation of the first stage of non-spherical bubble collapse near a wall and investigated the stress state inside the elastic material of the wall according to the change in stand-off distance g between the bubble and the wall. The relationship between the collapse behavior of the bubble and propagation of stress waves was confirmed for typical collapse modes: pancake-shaped mode at g = -0.3, hemispherical mode at g = 0, microjet mode at 0.3 < g < 1.0, and detaching mode at g > 1.2. The stress influence area, which is an index of material damage, was estimated. At 0.3 < g < 1.0, the stress influence area caused by the microjet is narrow and shallow in the material; in contrast, that by the pressure waves spreads more widely and deeply, especially inside the material. This means that the pressure wave has a larger influence than the microjet on damage to a material even though the maximum value of the equivalent stress is nearly identical between the microjet and pressure wave. Additionally, the depth of the stress influence area at 0.3 < g < 0.5 is larger than that at g = 0, although the volume and the maximum stress are larger at g = 0 than at 0.3 < g < 0.5. This indicates that the case of toroidal bubble rebound attaching to a wall has the potential to cause deeper damage inside a material in comparison with hemispherical bubble collapse.

Revealing the origins of vortex cavitation in a Venturi tube by high speed X-ray imaging

“…9 , Fig. 10 reveal the typical aspects of vortex cavitation arising in the Venturi tube observed by visible light and X-rays, as the shape and void ratio are closely related to the bubble collapse impact [38] , [39] . As mentioned previously, the conventional view is that vortex cavitation consists of small spherical bubbles.…”

“…10 was about 1.2 mm at 0.681 ms and 0.8 mm at 0.926 ms. From these observations it is clear that the bubbles in the vortex core are not spherical bubbles, but consist rather of the angulated bubbles. This is very important for simulating the cavitating flow numerically, as the impact of bubble collapse near the solid wall strongly depends on the bubble shape [38] , [39] .…”

“…In conventional numerical simulations of cloud cavitation, it is assumed that cloud cavitation consists of small spherical bubbles. However, recent numerical and experimental investigations of bubble dynamics have suggested that the intensity of a single bubble collapse is strongly affected by the geometry of the bubble and the distance between the bubble and the rigid wall [38] , [39] . Higher fidelity simulation of cavitation can be achieved using conventional computational fluid dynamics if bubbles could be assumed to be non-spherical.…”

Revealing the Origins of Vortex Cavitation in a Venturi Tube by High Speed X-Ray Imaging

“…To precisely investigate the bubbles in vortex cavitation, Figs. 9 and 10 reveal the typical aspects of vortex cavitation arising in the Venturi tube observed by visible light and X-rays, as the shape and void ratio are closely related to the bubble collapse impact [38,39]. As mentioned previously, the conventional view is that vortex cavitation consists of small spherical bubbles.…”

Laser Cavitation Peening: A Review

“…As shown in Figure 1, the development of a microjet in a spherical cavitation bubble is an interesting phenomenon, and some researchers believe that the microjet during cavitation bubble collapse can be utilized for peening. It has been demonstrated numerically, using fluid/material-coupled numerical simulations, that the pressure produced by the collapse of a hemispherical bubble is much stronger than that of microjettype collapse, as shown in Figure 2 [35]. In Figure 2, the black line shows the shape of the bubble changing with time, and the color contour reveals the pressure in the fluid and the equivalent stress in the material at bubble collapse.…”