A three-dimensional modeling for coalescence of multiple cavitation bubbles near a rigid wall

Abstract

Boundary Integral Method (BIM) has been widely and successfully applied to cavitation bubble dynamics, however, the physical complexities involved in the coalescence of multiple bubbles are still challenging for numerical modelling. In this study, an improved three-dimensional (3D) BIM model is developed to simulate the coalescence of multiple cavitation bubbles near a rigid wall, including an extreme situation when cavitation bubbles are in contact with the rigid wall. As the first highlight of the present model, a universal topological treatment for arbitrary coalescence is proposed for 3D cases, combined with a density potential method and an adaptive remesh scheme to maintain a stable and high-accuracy calculation. Modelling for the multiple bubbles attached to the rigid boundary is the second challenging task of the present study. The effects of the rigid wall are modelled using the method of image, thus the boundary value problem is transformed to the coalescence of real bubbles and their images across the boundary. Additionally, the numerical difficulties associated with the splitting of a toroidal bubble and self-coalescence due to the self-film-thinning process of a coalesced bubble are successfully overcome. The present 3D model is verified through convergence studies and further validated by the purposely conducted experiments. Finally, representative simulations are carried out to elucidate the main features of a coalesced bubble near a rigid boundary and the flow fields are provided to reveal the underlying physical mechanisms.

Theoretical study on bubble dynamics under hybrid-boundary and multi-bubble conditions using the unified equation

“…Some special phenomena, such as the mutual penetration between bubbles and fine thin jets, are found by Liang et al [47] and Tomita et al [48]. When the bubble buoyancy effect is considered, the bubble jet direction is deflected upward [49,50], altering the bubble migration direction. When the third bubble is included, it enhances or weakens the strength of the bubble jets generated by the other two bubbles depending on the phase and size difference of the three bubbles [51].…”

The jet characteristics of bubbles near mixed boundaries

“…In terms of numerical simulations, significant efforts have been made in recent years. [20][21][22][23][24][25][26] Wang 27 analyzed the motion of bubbles with a free surface near an inclined solid wall with the boundary element method (BEM), which provides a reference for studying the interaction between the bubble and mixed boundaries. However, this work assumed that the wall is semi-infinite, with no influence from a bottom surface.…”

Manipulation of bubble collapse patterns near the wall of an adherent gas layer

“…Cavitation bubbles underwater undergo the process of bubble generation, expansion, contraction, collapse, and rebound [14] . When a rigid wall is nearby, the cavitation bubbles will produce jets toward the wall during the collapse stage due to the pressure difference [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] . The high-speed jet and high pressure [16] , [22] generated during the collapse process are the reasons for the destruction of the wall material.…”