Single cavitation bubble dynamics in a stagnation flow

Abstract

Jetting of collapsing bubbles is a key aspect in cavitation-driven fluid–solid interactions as it shapes the bubble dynamics and additionally due to its direct interaction with the wall. We study experimentally and numerically the near-wall collapse and jetting of a single bubble seeded into the stagnation flow of a wall jet, i.e. a jet that impinges perpendicular onto a solid wall. High-speed imaging shows rich and rather distinct bubble dynamics for different wall jet flow velocities and bubble-to-wall stand-off distances. The simulations use a volume-of-fluid method that allows us to numerically determine the microscopic and transient pressures and shear stresses on the wall. It is shown that a wall jet at moderate flow velocities of a few metres per second already shapes the bubble ellipsoidally inducing a planar and convergent jet flow. The distinct bubble dynamics allow us to tailor the wall interaction. In particular, the shear stresses can be increased by orders of magnitude without increasing impact pressures the same way. Interestingly, at small seeding stand-offs, the bubble during the final collapse stage can lift off the wall and migrate against the flow direction of the wall jet such that the violent collapse occurs away from the wall.

Numerical Modeling of the Behavior of Bubble Clusters in Cavitation Processes

“…Thus, the bubble oscillates at a high frequency, dissipating part of the energy into the liquid due to the thermal conductivity and viscosity of the liquid, as well as due to the emission of an acoustic pressure pulse in the form of a shock wave. Before the final collapse, the bubble, judging by visual observations [10,18,[74][75][76][77], manages to make 2-5 oscillations. Figures 2 and 3 show how strongly the values of the kinematic, thermophysical, and energy parameters characterizing the dynamic abilities of the bubble change at the stage of its maximum compression over a period of time ∆τ ≈ 10 ns.…”

“…Cavitation can also be initiated for other tasks, such as emulsification, sonophoresis, and homogenization [14][15][16][17]. Jet flows formed during a cavitation bubble collapse can reach a velocity of 80 m/s and can be used for microfluidic pumping and to create vortices for vigorous short-term mixing in microfluidic devices [18][19][20][21][22][23][24].…”

Dynamics of a cavitation bubble confined in a thin liquid layer at null Kelvin impulse

“…26 While the implications of a net null Kelvin impulse environment on bubble dynamics have been addressed in the past, it was often pursued as a limiting case where the directionality of the overall bubble displacement and the resulting jetting phenomena changes, i.e., neutral bubble collapse. Researchers have thus far considered either stagnation flow 26,29,35,36 or a combination of buoyant forces counteracted by the effects of various boundaries, ranging from rigid and composite boundaries to free surfaces and liquid interfaces. 26,29,35,37,38 An important consideration here is that the anisotropy parameter f in both gravitational fields and stationary potential flows is not scale-independent.…”

Study on the influence of ultrasound on the kinetic behaviour of hydrogen bubbles produced by proton exchange membrane electrolysis with water

“…Thermal effect is the role of ultrasound in the medium, when the medium of ultrasonic absorption caused by their own temperature rise, the higher the frequency of ultrasonic vibration, the more significant thermal absorption phenomenon [3] , [4] . Cavitation effect is when the ultrasonic propagation into the medium to generate positive and negative pressure alternating cycle, exists in the liquid micro gas nuclei in the ultrasonic field stretching and squeezing under the action of vibration, growth to contraction, collapse and closure of the process, at the moment of collapse of cavitation bubbles in the liquid locally generated high temperature and high pressure [5] , [6] , [7] , [8] . The mechanical effect is the ultrasonic effect on the medium when the power of mechanical vibration of the mass.…”