Structural dynamics of water in a supersonic shockwave

Vassholz, Malte; Hoeppe, Hannes Paul; Hagemann, J.; Rosselló, Juan Manuel; Osterhoff, Markus; Mettin, Robert; Möller, Johannes; Scholz, Markus; Boesenberg, Ulrike; Hallmann, Jörg; Kim, Chan; Zozulya, Alexey; Lu, Wei; Shayduk, Roman; Madsen, Anders; Salditt, Tim

doi:10.1063/5.0131457

Cited by 8 publications

(2 citation statements)

References 48 publications

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“…The use of very small amounts of liquid prevents the x-rays from being fully absorbed by the sample, thus improving the contrast of the x-ray images. This technique is suitable to study the properties of opaque liquids without optical aberrations, it is less sensitive to distortions produced by wavy surfaces, and also allows retrieving information about the liquid density changes produced by the passage of the pressure waves (Vassholz et al 2021(Vassholz et al , 2023, which represents an advantage over traditional optical imaging.…”

Section: Introductionmentioning

confidence: 99%

Bubble nucleation and jetting inside a millimetric droplet

et al. 2023

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In this work we present experiments and simulations on the nucleation and successive dynamics of laser-induced bubbles inside liquid droplets in free-fall motion, i.e. a case where the bubbles are subjected to the influence of a free boundary in all directions. Within this spherical millimetric droplet, we have investigated the nucleation of secondary bubbles induced by the rarefaction wave that is produced when the shock wave emitted by the laser-induced plasma reflects at the drop surface. Interestingly, three-dimensional clusters of cavitation bubbles are observed. Their shape is compared with the negative pressure distribution computed with a computational fluid dynamics model and allows us to estimate a cavitation threshold value. In particular, we observed that the focusing of the waves in the vicinity of the free surface can give rise to explosive cavitation events that end up in fast liquid ejections. High-speed recordings of the drop/bubble dynamics are complemented by the velocity and pressure fields simulated for the same initial conditions. The effect of the proximity of a curved free surface on the jetting dynamics of the bubbles was qualitatively assessed by classifying the cavitation events using a non-dimensional stand-off parameter ${\Upsilon\hskip -1,05em -\,}$ that depends on the drop size, the bubble maximum radius and the relative position of the bubble inside the drop. Additionally, we studied the role of the drop's curvature by implementing a structural similarity algorithm to compare cases with bubbles produced near a flat surface to the bubbles inside the drop. Interestingly, this quantitative comparison method indicated the existence of equivalent stand-off distances at which bubbles influenced by different boundaries behave in a very similar way. The oscillation of the laser-induced bubbles promotes the onset of Rayleigh–Taylor and Rayleigh–Plateau instabilities, observed on the drop's surface. This phenomenon was studied by varying the ratio of the maximum radii of the bubble and the drop. The specific mechanisms leading to the destabilisation of the droplet surface were identified.

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Section: Introductionmentioning

confidence: 99%

Bubble nucleation and jetting inside a millimetric droplet

et al. 2023

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“…More recently, time-resolved x-ray imaging has become a valuable technique to investigate fast hydrodynamic processes [23][24][25][26][27][28][29][30], especially with the development of hard x-ray free-electron laser (XFEL) sources. A unique feature of x-ray imaging is a quantitative phase contrast mechanism, which gives direct access to the projected electron density of the sample (or mass density in case of a homogeneous object).…”

Section: Introductionmentioning

confidence: 99%

The collapse of a sonoluminescent cavitation bubble imaged with X-ray free-electron laser pulses

Hoeppe,

Osterhoff,

Aghel Maleki

et al. 2024

New J. Phys.

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Single bubble sonoluminescence (SBSL) is the phenomenon of synchronous light emission due to the violent collapse of a single spherical bubble in a liquid, driven by an ultrasonic field. During the bubble collapse, matter inside the bubble reaches extreme conditions of several gigapascals and temperatures on the order of 10 000 K, leading to picosecond flashes of visible light. To this day, details regarding the energy focusing mechanism rely on simulations due to the fast dynamics of the bubble collapse and spatial scales below the optical resolution limit. In this work we present phase-contrast holographic imaging with single XFEL pulses of a SBSL cavitation bubble in water. X-rays probe the electron density structure and by that provide a uniquely new view on the bubble interior and its collapse dynamics. The involved fast time-scales are accessed by sub-100 fs XFEL pulses and a custom synchronization scheme for the bubble oscillator. We find that during the whole oscillation cycle the bubble’s density profile can be well described by a simple step-like structure, with the radius R following the dynamics of the Gilmore model. The quantitatively measured internal density and width of the boundary layer exhibit a large variance. Smallest reconstructed bubble sizes reach down to R ≃0.8 μm, and are consistent with spherical symmetry. While we here achieved a spatial resolution of a few 100 nm, the visibility of the bubble and its internal structure is limited by the total X-ray phase shift which can be scaled with experimental parameters.

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Jetting bubbles observed by x-ray holography at a free-electron laser: internal structure and the effect of non-axisymmetric boundary conditions

Rosselló,

Hoeppe,

Koch

et al. 2024

Exp Fluids

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In this work, we study the jetting dynamics of individual cavitation bubbles using x-ray holographic imaging and high-speed optical shadowgraphy. The bubbles are induced by a focused infrared laser pulse in water near the surface of a flat, circular glass plate, and later probed with ultrashort x-ray pulses produced by an x-ray free-electron laser (XFEL). The holographic imaging can reveal essential information of the bubble interior that would otherwise not be accessible in the optical regime due to obscuration or diffraction. The influence of asymmetric boundary conditions on the jet’s characteristics is analysed for cases where the axial symmetry is perturbed and curved liquid filaments can form inside the cavity. The x-ray images demonstrate that when oblique jets impact the rigid boundary, they produce a non-axisymmetric splash which grows from a moving stagnation point. Additionally, the images reveal the formation of complex gas/liquid structures inside the jetting bubbles that are invisible to standard optical microscopy. The experimental results are analysed with the assistance of full three-dimensional numerical simulations of the Navier–Stokes equations in their compressible formulation, which allow a deeper understanding of the distinctive features observed in the x-ray holographic images. In particular, the effects of varying the dimensionless stand-off distances measured from the initial bubble location to the surface of the solid plate and also to its nearest edge are addressed using both experiments and simulations. A relation between the jet tilting angle and the dimensionless bubble position asymmetry is derived. The present study provides new insights into bubble jetting and demonstrates the potential of x-ray holography for future investigations in this field.

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Structural dynamics of water in a supersonic shockwave

Cited by 8 publications

References 48 publications

Bubble nucleation and jetting inside a millimetric droplet

Bubble nucleation and jetting inside a millimetric droplet

The collapse of a sonoluminescent cavitation bubble imaged with X-ray free-electron laser pulses

Jetting bubbles observed by x-ray holography at a free-electron laser: internal structure and the effect of non-axisymmetric boundary conditions

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