Laser-induced cavitation bubbles and shock waves in water near a concave surface

Tomaž Požar (Author), Vid Agrež (Author), Rok Petkovšek (Author)

Abstract

The interplay among the cavitation structures and the shock waves following a nanosecond laser breakdown in water in the vicinity of a concave surface was visualized with high-speed shadowgraphy and schlieren cinematography. Unlike the generation of the main cavitation bubble near a flat or a convex surface, the concave surface refocuses the emitted shock waves and causes secondary cavitation near the acoustic focus which is most pronounced when triggered by the shock wave released during the first main bubble collapse. The shock wave propagation, reflection from the concave surface and its scattering on the dominant cavity is clearly resolvable on the shadowgraphs. The schlieren approach revealed the pressure build up in the last stage of the collapse and the first stage of the rebound. A persistent low-density watermark is left behind the first collapse. The observed effects are important wherever cavities collapse near indented surfaces, such as in cavitation peening, cavitation erosion and ophthalmology.

Keywords

cavitation bubble;shock wave;acoustic focusing;secondary cavitation;laser breakdown;

Data

Language:	English
Year of publishing:	2021
Typology:	1.01 - Original Scientific Article
Organization:	UL FS - Faculty of Mechanical Engineering
UDC:	532.528:535(045)
COBISS:	45742083
ISSN:	1350-4177
Views:	345
Downloads:	163
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	Slovenian
Secondary abstract:	Medsebojno delovanje kavitacijskih struktur in udarnih valov po nanosekundnem laserskem preboju v vodi v bližini konkavne površine je bilo vizualizirano s hitrimi senčnimi slikami in schlieren kinematografijo. Za razliko od nastanka glavnega kavitacijskega mehurčka v bližini ravne ali konveksne površine konkavna površina ponovno fokusira oddane udarne valove in povzroči sekundarno kavitacijo v bližini akustičnega fokusa. Ta je najbolj izrazita, ko jo sproži udarni val, ki se izseva pri prvem kolapsu glavnega mehurčka. Na senčnih slikah je jasno razvidno širjenje udarnega vala, njegov odboj od konkavne površine in njegovo sipanje na glavnem mehurčku. S schlieren fotografijo smo zaznali povečanje tlaka v zadnji fazi kolapsa in začetni fazi odboja. Prvi kolaps mehurčka za seboj pusti trajni vodni žig z znižano gostoto vode. Opaženi učinki so pomembni tam, kjer mehurčki kolapsirajo v bližini udrtih površin, na primer pri kavitacijskem utrjevanju površin, kavitacijski eroziji in oftalmologiji.
Secondary keywords:	kavitacijski mehurček;udarni val;akustično fokusiranje;sekundarna kavitacija;laserski preboj;
Type (COBISS):	Article
Pages:	str. 1-11
Issue:	ǂVol. ǂ73
Chronology:	May 2021
DOI:	10.1016/j.ultsonch.2020.105456
ID:	12551115