Direct observation of shockwaves, cavitation, and jetting inside liquid droplets during high-speed impact

Agrež, Vid (author), Gonzalez-Avila, Silvestre Roberto (author), Horvat, Darja (author), Xie, Run-Ze (author), Zeng, Qingyun (author), Petkovšek, Rok (author), Ohl, Claus-Dieter (author)

This study reports direct experimental observations of shockwave propagation and cavitation bubble formation inside liquid water droplets during high-speed impact (80 –180 m/s) on solid surfaces, together with jetting observed at the distal end of the droplet. Ultra-high-speed shadowgraph and angle-view imaging at 10 million frames per second resolved two distinct internal wave structures: a primary compression front (1500–2050 m/s), consistent with pressure-dependent corrections to the acoustic wave speed, and a secondary tension wave emerging approximately 500 ns later, generated by reflection at the curved water–air interface. The curved distal surface focuses converging rarefaction waves into a caustic region, leading to cavitation nucleation 1.2–1.5 µs after impact. The subsequent asymmetric collapse of these cavitation structures drives directed jetting from the distal end, with jet morphology dependent on droplet geometry: coherent jets for smaller spherical droplets (<2 mm) whereas spray-like ejection is typical for larger, elongated droplets (>2 mm). At the proximal end of the droplet, air is entrapped between the surface and the droplet, collapsing into a toroidal-shaped bubble that exhibits oscillations in the 0.5–1.8 MHz range. All presented results, including experimental data and accompanying analysis, provide benchmark validation data for computational models of compressible droplet impact.

• Language: English
• Keywords: cavitation, droplet impact, shockwaves, acoustic focusing, high-speed imaging
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: Str. 1-13
• Numbering: Vol. 134, art. 108121
• PID: 20.500.12556/RUL-190890
• UDC: 532.528:004.932
• ISSN on article: 1873-2828
• DOI: 10.1016/j.ultsonch.2026.108121
• COBISS.SI-ID: 304216579
• Publication date in RUL: 06.11.2026

Record is a part of a journal

• Title: Ultrasonics Sonochemistry
• Publisher: Elsevier
• ISSN: 1873-2828
• COBISS.SI-ID: 23127813

Licences

• License: CC BY-NC 4.0, Creative Commons Attribution-NonCommercial 4.0 International
• Link: http://creativecommons.org/licenses/by-nc/4.0/
• Description: A creative commons license that bans commercial use, but the users don’t have to license their derivative works on the same terms.

Secondary language

• Language: Slovenian
• Keywords: kavitacija, trk kapljice, udarni valovi, akustično fokusiranje, visokohitrostno slikanje

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P2-0270-2022
• Name: Proizvodni sistemi, laserske tehnologije in spajanje materialov

• Funder: Other - Other funder or multiple funders
• Funding programme: Deutsche Forschungsgemeinschaft
• Project number: OH 75/12-1
• Name: /