Oscillation of an ultrasonically driven gas bubble in an asymmetric confined domain

This study investigates the behavior of an ultrasonically driven gas bubble between two parallel rigid circular walls with a cylindrical micro-indentation in one wall using OpenFOAM software.

The research focuses on determining conditions that facilitate particulate contamination removal from the indentation using bubble jets. By varying the dimensionless indentation diameter D, the researchers identified three distinct bubble collapse regimes: symmetrical collapse with two identical jets when D = 0, asymmetric collapse with two non-identical jets when 0 < D* < 4.9, and directed single jet formation when D* ≥ 4.9.

For values where 0 < D* < 4.9, the bubble splits into two smaller sub-bubbles during collapse, with the lower sub-bubble transforming into a toroidal shape whose high-speed liquid jet penetrates the indentation, effectively removing contamination particularly when D* < 4.

However, when D* ≥ 4.9, the lower sub-bubble completely vanishes, making contamination removal impossible. The study also successfully addressed numerical instability issues that arise at larger D* values through proper computational grid treatment.