Cavitation Inception from Transverse Waves in a Thin Liquid Gap

Abstract

It is well known that dielectric breakdown in a liquid generates cavitation bubbles and shock waves.Here we demonstrate that when the liquid is bounded by two solid glass boundaries (10-20-μm separation), rings of microscopic bubbles can be nucleated around the laser-induced cavitation bubble. While generally acoustic nucleation is achieved with longitudinal waves of sufficient tension, this work demonstrates that acoustic cavitation can also be generated from transverse waves. Our experiments identify three waves originating at the boundaries: the fastest is the bulk wave in the solid, followed by a leaky Rayleigh wave at the liquid-solid contact, which is trailed by a Lamb-type wave. For the latter, the two solid boundaries act as a wave guide and generate intense and short-lived cavitation activity within the gap. Streak photography and high-speed photography reveal the microsecond-duration cavitation-bubble dynamics, and subpicosecond strobe photography visualizes the mechanism of bubble nucleation from the accelerated surface. Simulations coupling the solid mechanics with the acoustics support the experimentally observed mechanisms of transverse-wave-induced cavitation inception.

Questioning the ASTM G32-16 (stationary specimen) standard cavitation erosion test

“…The collapse of the cylindrical bubble is much slower – compared to the spherical case it takes more than twice the time for it to collapse completely. This is consistent with the observations and simulations for even thinner (nanometric) gaps [42] . At the collapse of the bubble a shock wave is generated, which at its origin, also triggers the Lamb wave in the plates (see video material in the supplementary).…”

“…Following this, the bubble collapses symmetrically (cylindrically) and the minimum size is reached at about t = 342 μs. In the final image of the sequence at t = 348 μs one can again observe very small bubbles scattered in radial direction from the point of the main bubble collapse – this is again a result of the Lamb wave that progressed at a very high velocity through the glass plates and creating a momentary low pressure region in its wake [42] .…”

“…One can also notice that the shock is less pronounced than in the case of spherical bubble. This is likely due to the presence of many small cavities which form due to the momentary pressure drop during the transition of the Lamb wave – an elastic wave that propagates at very high velocity (>3000 m/s) through the upper and lower glass plate with the amplitude perpendicular to the plate (see [42] ). The occurrence of the Lamb wave is specific to this particular experiment ( Fig.…”

Controlled inertial nano-cavitation above 100 MHz

“…Cavitation has also been produced via surface acoustic waves (SAWs; Rapet, Quinto-Su & Ohl 2020), also known as Rayleigh waves, which propagate along the surface of an elastic material (Rayleigh 1886). Their amplitude decays exponentially with the distance from the surface (depth), and most of the energy carried by the wave is concentrated in just one wavelength below the surface.…”

Acoustic characterization of cavitation intensity: A review

“…Seventy years ago, cavitation intensity, as a self-evident concept, has appeared in the literature [36] . However, for a long time, a common and clear definition of cavitation intensity is rarely found, although chemical method [37] , [38] , [39] , acoustic method [40] , [41] , [42] , [43] , optical method [44] , [45] , [46] , [47] , [48] , mechanical method [49] , [50] , [51] , [52] , electrochemical method [53] , hybrid method [54] , [55] , [56] , [57] , [58] , [59] , [60] have been used to measure the cavitation intensity.…”