Abstract:Investigations of shock-induced cavitation within a droplet are highly challenged by the multiphase nature of the mechanisms involved. Within the context of heterogeneous nucleation, we introduce a thermodynamically well-posed multiphase numerical model accounting for phase compression and expansion, which relies on a finite pressure-relaxation rate formulation. We simulate (i) the spherical collapse of a bubble in a free field, (ii) the interaction of a cylindrical water droplet with a planar shock wave, and … Show more
“…2016) or, as we already mentioned, a drop (Obreschkow et al. 2006; Gonzalez-Avila & Ohl 2016; Kondo & Ando 2016; Kyriazis, Koukouvinis & Gavaises 2018; Wu, Xiang & Wang 2018 b ; Wu, Liu & Wang 2021; Biasiori-Poulanges & Schmidmayer 2023). Laser cavitation in some of these configurations was lately applied in studies involving x-ray holography or x-ray diffraction to investigate the propagation of shock waves in liquids (Stan et al.…”
Section: Introductionmentioning
confidence: 80%
“…(2016) subjected a water column to a single shock wave and found a cavitation threshold between 0.42 and 2.33 MPa. Biasiori-Poulanges & Schmidmayer (2023) compared numerical simulations and experiments of a liquid drop subjected to a planar shock wave and found a threshold between 0.37 and 2.4 MPa. A similar shock front can be found when a droplet impacts on a solid surface at a high speed (e.g.…”
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.
“…2016) or, as we already mentioned, a drop (Obreschkow et al. 2006; Gonzalez-Avila & Ohl 2016; Kondo & Ando 2016; Kyriazis, Koukouvinis & Gavaises 2018; Wu, Xiang & Wang 2018 b ; Wu, Liu & Wang 2021; Biasiori-Poulanges & Schmidmayer 2023). Laser cavitation in some of these configurations was lately applied in studies involving x-ray holography or x-ray diffraction to investigate the propagation of shock waves in liquids (Stan et al.…”
Section: Introductionmentioning
confidence: 80%
“…(2016) subjected a water column to a single shock wave and found a cavitation threshold between 0.42 and 2.33 MPa. Biasiori-Poulanges & Schmidmayer (2023) compared numerical simulations and experiments of a liquid drop subjected to a planar shock wave and found a threshold between 0.37 and 2.4 MPa. A similar shock front can be found when a droplet impacts on a solid surface at a high speed (e.g.…”
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.
“…In figure 5( a ), the NPP point's location with water is marked by solid squares, while with -hexane it is shown with hollow squares in figure 5( b ). Following Biasiori-Poulanges & Schmidmayer (2023), an optimal pressure relaxation rate of 3.5 for shock-droplet interaction is recommended, along with positioning the cavitation bubble cloud's centre 1.5 times away from the origin than the focus point (with the right as the positive direction). Figure 4.Schematic diagram of the NPP point with the black dot inside the droplet.Figure 5.Comparison of the NPP point's location obtained from the numerical simulation results with experimental measurements and theoretical results for ( a ) water and ( b ) -hexane.…”
Section: Results Of the Npp Pointmentioning
confidence: 99%
“…Here, β ref ,k represents the disturbance angle with k reflections of the ray. Previous research (Wu et al 2018;Biasiori-Poulanges & El-Rabii 2021;Xu et al 2023) indicates that the one-time reflected rays are responsible for generating negative pressure; therefore, other rays are not considered in this figure.…”
Section: Improvement To the Original Theoretical Modelmentioning
confidence: 99%
“…gas–liquid interface) of the droplet, creating a negative peak pressure (NPP) point that triggers cavitation. Biasiori-Poulanges & Schmidmayer (2023) conducted a phenomenological analysis of shock-induced cavitation in droplets using a multi-phase modelling approach. The critical pressure relaxation rate crucial to the numerical model was ascertained by comparing numerical outcomes with the Keller–Miksis model and related experiments.…”
Shock–droplet interaction in the early stage involves intricate wave structures. Investigating this phenomenon is inherently challenging due to the fine spatial and temporal scales involved. Past research has suggested that the occurrence of cavitation, marked by a negative peak pressure, is linked to the focus of the reflected expansion wave. In this study, a high-fidelity compressible numerical approach is utilized to replicate the initial phase of shock–droplet interactions. The location of the negative peak pressure is meticulously documented and compared with experimental measurement and numerical results. Results indicate a strong alignment between the negative peak pressure positions identified through numerical simulations and the focal points identified in theoretical models for low gas–liquid wave velocity ratios. However, this alignment is notably disrupted when dealing with higher gas–liquid wave velocity ratios. Further enhancements are made to the theoretical model, enabling a more precise depiction of internal wave structures and focus points, particularly under conditions of high gas–liquid wave velocity ratios. The study delves into the various factors influencing internal pressure fluctuations within the liquid droplet, categorizing them into four phases: the shock wave effect, relaxation effect, fluctuation effect, and expansion wave effect. Analysing the pressure decrease portion reveals that while the converging of the reflected expansion wave leads to a substantial pressure drop, it accounts for only a fraction of the total pressure variation. Consequently, any model predicting negative peak pressure positions must comprehensively consider all contributing factors.
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