When a droplet hits a surface fast enough, droplet splashing can occur: Smaller secondary droplets detach from the main droplet during impact. While droplet splashing on smooth surfaces is by now well understood, the surface roughness also affects at which impact velocity a droplet splashes. In this paper, the influence of the surface roughness on droplet splashing is investigated. By changing the root-mean-square roughness of the impacted surface, we show that the droplet splashing velocity is only affected when the droplet roughness is large enough to disrupt the spreading droplet lamella and change the droplet splashing mechanism from corona to prompt splashing. Finally, using Weber and Ohnesorge number scaling models, we also show that the measured splashing velocity for both water and ethanol on surfaces with different roughnesses and water-ethanol mixtures collapses onto a single curve, showing that the droplet splashing velocity on rough surfaces scales with the Ohnesorge number defined with the surface roughness length scale.

中文翻译：

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水滴飞溅在粗糙表面上

当液滴以足够快的速度撞击表面时，可能会发生液滴飞溅：较小的次要液滴在撞击过程中会与主液滴分离。尽管现在已经很好地理解了液滴在光滑表面上的飞溅，但是表面粗糙度也影响液滴飞溅的冲击速度。本文研究了表面粗糙度对液滴飞溅的影响。通过改变受影响表面的均方根粗糙度，我们表明，只有当液滴粗糙度足够大以至于破坏散布的液滴薄片并将液滴飞溅机制从电晕改变为迅速飞溅时，液滴飞溅速度才会受到影响。最后，使用Weber和Ohnesorge数字缩放模型，