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Updated: Sep 13, 2025

Visualization of High Speed Liquid Jet Impaction on a Moving Surface
Published on: April 17, 2015
Singular jets with beads-on-a-string structures during the impact of elasto-viscoplastic droplets on superhydrophobic
Xiaoyun Peng1, Tianyou Wang2, Zhizhao Che2
1State Key Laboratory of Engines, Tianjin University, Tianjin, 300350, China.
Hypothesis:
A singular jet, as a phenomenon caused by flow singularity, is an important process for the transport of liquid in an extensive range of applications. New singular jet dynamics are expected during the impact of droplets of different non-Newtonian fluids.
Experiments:
We study the impact of elasto-viscoplastic (EVP) droplets on super-hydrophobic surfaces via high-speed imaging, digital image processing, and theoretical analysis, focusing on the singular jet. The key steps of EVP droplet impact are quantitatively analyzed, including cavity collapse in the droplet retraction stage and liquid column stretching and pinch-off in the jet formation stage.
Findings:
A new type of singular jet is identified, namely singular jet with beads-on-a-string (BOAS) structure, instead of the singular jet of Newtonian droplets in impacting processes studied before. During cavity collapse dynamics, EVP droplets exhibit similarities to Newtonian droplets in two key aspects: the temporal evolution of cavity diameter obeys a power-law dependence with an exponent of 1/2, and the jet velocity demonstrates a radius-dependent scaling behavior with an exponent of -1. In the process of liquid column stretching and pinching off, the liquid column pinch-off time changes from the inertial-capillary mechanism to the elastic-capillary mechanism. We analyze the distribution of BOAS singular jets depending on the Weber (We) number and EVP fluid concentration, and determined the critical conditions required for BOAS singular jet formation.
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