Liu Yuan, Tan Peng, Xu Lei
Department of Physics, The Chinese University of Hong Kong, Hong Kong, China; and.
Department of Physics, The Chinese University of Hong Kong, Hong Kong, China; and State Key Laboratory of Surface Physics, Department of Physics, Fudan University, Shanghai 200433, China
Proc Natl Acad Sci U S A. 2015 Mar 17;112(11):3280-4. doi: 10.1073/pnas.1417718112. Epub 2015 Feb 23.
When a fast-moving drop impacts onto a smooth substrate, splashing will be produced at the edge of the expanding liquid sheet. This ubiquitous phenomenon lacks a fundamental understanding. Combining experiment with model, we illustrate that the ultrathin air film trapped under the expanding liquid front triggers splashing. Because this film is thinner than the mean free path of air molecules, the interior airflow transfers momentum with an unusually high velocity comparable to the speed of sound and generates a stress 10 times stronger than the airflow in common situations. Such a large stress initiates Kelvin-Helmholtz instabilities at small length scales and effectively produces splashing. Our model agrees quantitatively with experimental verifications and brings a fundamental understanding to the ubiquitous phenomenon of drop splashing on smooth surfaces.
当一个快速移动的液滴撞击到光滑的基底上时，在扩展液膜的边缘会产生飞溅。这种普遍存在的现象尚缺乏基本的理解。通过将实验与模型相结合，我们阐明了被困在扩展液面前方的超薄气膜引发了飞溅。由于该气膜比空气分子的平均自由程更薄，内部气流以与声速相当的异常高速度传递动量，并产生比常见情况下气流强10倍的应力。如此大的应力在小尺度上引发了开尔文-亥姆霍兹不稳定性，并有效地产生了飞溅。我们的模型与实验验证在定量上相符，并为光滑表面上液滴飞溅这一普遍现象带来了基本的理解。
