Velocity characteristics of microjets generated by double bubbles near a rigid wall under ultrasound

The cavitation bubble collapse and associated microjets are widely used in ultrasound and chemical engineering. However, much remains to be known about the interplay of double bubbles and their microjets. The dynamic models for the single-bubble and double-bubble near the rigid wall under ultrasound were constructed and numerically solved to reveal the bubble collapse behavior. Results indicates that compared to a free wall, rigid walls have a strong inhibitory effect on the collapse of a single bubble, but have a certain promoting effect on the collapse of double bubbles. The double bubbles have a higher velocity and smaller range of initial bubble radii than a single bubble to produce microjets. When the bubble is close to the stiff wall, the microjet of a single bubble is always stronger than that of double bubbles. But when bubbles move away from rigid walls, the microjet velocity of double bubbles may be greater than that of a single bubble. Compared with the single bubble, the double bubbles can generate microjets with a narrower range of the ultrasound pressure amplitude and a smaller ultrasound frequency. The study will give new insights into the velocity of microjets in ultrasonic related processing applications.