The unexpectedly low cavitation inception threshold of water is widely attributed to the presence of cavitation nuclei either in the bulk water or attached to immersed surfaces. Being compressible, such objects are expected to respond to modest tensile stresses. Surprisingly, a large corpus of experiments shows that micro- and nanobubbles attached to planar smooth surfaces are unresponsive to tensile stresses, seemingly ruling out their ability to serve as cavitation nuclei. Here, using optical microscopy we show that, although these surface micro- and nanobubbles are not directly responsive to tensile stresses induced by a nearby cavitation bubble, strong short-lived shear flows induced by cavitation jetting cause tethers to extend from the surface micro- and nanobubbles and lead to the pinch-off of daughter bubbles. Our results show a unique and previously unanticipated mechanism for the generation of cavitation nuclei.

中文翻译：

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强剪切流从表面的微气泡和纳米气泡释放出气态核

水的空化起始阈值出乎意料的低，这广泛归因于大量水中或附着在浸没表面上的空化核的存在。由于是可压缩的，因此预期此类物体会响应适度的拉应力。出乎意料的是，大量的实验表明，附着在平面光滑表面上的微气泡和纳米气泡对拉应力没有反应，似乎排除了它们充当空化核的能力。在这里，我们使用光学显微镜表明，尽管这些表面微气泡和纳米气泡并不直接响应附近空化气泡引起的拉伸应力，但是空化喷射引起的强烈的短时剪切流会导致系链从表面微细结构延伸。纳米气泡并导致子气泡被夹住。